I MSI!

Institute for Materials Science and Engineering

POUTMERS

NAS-NRC

Assessment Panel

November 16-17, 1988

NISTIR 88-3842

U.S. Department of Commerce

National Institute of Standards

and Technology >yy

Technical Activities

1988
Idealized representation of the

molecular packing of a novel liquid

crystalline diacetylene monomer

and resulting polymer. The reactive

diacetylene unit composed of

alternating triple-single-triple

bonds forms the core of the rigid

mesogenic unit, represented by the

blackened rectangle, of the liquid

crystalline monomer. Polymerization

within the various smectic and

nematic liquid crystal phases gives

rise to an organized pi-conjugated

polymer structure composed of an

alternating single-triple-single-double

bond backbone repeat unit.

Polydiacetylenes are of strong

theoretical and technological interest

in the expanding field of nonlinear

optical polymers and integrated

optics.
Institute for Materials Science and Engineering

POUTMERS

LE. Smith, Chief

B.M. Fanconi, Deputy

NAS-NRC

Assessment Panel

November 16-17, 1988

NISTIR 88-3842

U.S. Department of Commerce

National Institute of Standards and

Technology

Technical Activities

1988

POLYMERS DIVISION

CHIEF

Leslie E. Smith

Phone: (301) 975=6762

DEPUTY CHIEF

Bruno M. Fanconi

Phone: (301) 975=6770

ASSISTANT CHIEF'

Martin G. Broadhurst

Phone: (301) 975=6765

GROUP LEADERS

Electrical Properties

G. Thomas Davis

Phone: (301) 975-6725

Chemical Performance & Standards

Francis W. Wang

Phone: (301) 975-6726

Mechanical Performance

Bruno M. Fanconi

Phone: (301) 975-6770

Polymer Composites

Donald L. Hunston

Phone: (301) 975-6837

Polymer Blends

Charles C t Han

Phone: (301) 975-6771

Dental & Medical Materials

John A. Tesk

Phone: (301) 975-6801

Polymers

Division

LESLIE E. SMITH, Chief. Dr.

Smith was born in New York. He

earned degrees in chemistry from

Case Institute of Technology and

Catholic University. Except for a

three year period of graduate study,

he has been with NBS since 1964.

BRUNO M. FANCONI, Deputy

Chief. Dr. Fanconi was born in Merced, California. He earned

degrees in physical chemistry from

the University of California at Los

Angeles and the University of

Washington. He joined the staff of

NBS in 1971.

MARTIN G. BROADHURST,

Assistant Chief. Dr. Broadhurst was

born in Washington, D.C., and

earned degrees in physics at Western

Maryland College and Pennsylvania

State University. After teaching at Pennsylvania State, he joined NBS in 1960.

G. THOMAS DAVIS, Group

Leader, Electrical Properties. Dr.

Davis was born in Montour Falls,

New York. He earned degrees in chemical engineering at Cornell

University and physical chemistry at Princeton University. Prior to joining NBS in 1964, he worked for Esso

Research and Engineering Co. and

taught at the University of Virginia.

FRANCIS W. WANG, Group

Leader, Chemical Performance and

Standards. Dr. Wang was born in Peikang, Taiwan. He earned the B.S.

and M.S. in chemical engineering at California Institute of Technology

and the Ph.D. in physical chemistry

at the University of California, in San

Diego. He joined the staff of NBS in 1972 after a postdoctoral period at the Polytechnic Institute of New

York.

DONALD L. HUNSTON, Group

Leader, Polymer Composites. Dr.

Hunston was born in Springfield,

MI. He earned degrees in mathematics and chemistry at Kent State University. Prior to joining NBS in 1980, he was a Postdoctoral Fellow at Northwestern University and worked

in the Chemistry Division at the

Naval Research Laboratory.

JOHN A. TESK, Leader, Dental and

Medical Materials. Dr. Tesk was

born in Chicago, Illinois. He holds

the degrees of B.S., M.S. in

Metallurgy and Ph.D. in Materials

Science from Northwestern University. Prior to joining NBS in 1978, he was at the University of Illinois,

Chicago, on the staff at Argonne National Laboratory, Director of R&D

with the Dental Division of

Howmedica, Inc. and Director of

Education Services at IGT.

CHARLES C. HAN, Group Leader,

Polymer Blends. Dr. Han was born

in Szuchuan, China. He earned his B.S. in chemical engineering at National Taiwan University, M.S. in physical chemistry at the University

of Houston and his Ph.D at the

University of Wisconsin. He joined

the staff of NBS in 1974.

BRUNO M. FANCONI, Group

Leader, Mechanical Performance.
'mm
TABLE OF CONTENTS PAGE

INTRODUCTION ........... .............. iii

RESEARCH STAFF vii

TECHNICAL ACTIVITIES ....... .............. 1

ELECTRICAL PROPERTIES. 1

FY 88 Accomplishments. ....................... 2

Automated Dielectric Measurements 2

Thermal Pulse Measurements of Polarization and Space Charges .... 4

Ferroelectric Polymers ............. 6

Nonlinear Optical Properties of Polymers .............. 8

POLYMER STANDARDS AND CHEMICAL PERFORMANCE ................ 11

FY 88 Accomplishments. ..... ............. 12

Standard Reference Materials 13

Polymer Processing ..... ...... 15

Molecular Characterization ............... 17

Bioprocessing 19

Biomolecular Characterization - Inorganic Materials. ........ 22

MECHANICAL PERFORMANCE OF POLYMERS 24

FY 88 Accomplishments. 24

Characterization of the Solid State Structure and Morphology .... 25

Measurement and Modeling of Mechanical Properties and Performance. . 31

POLYMER COMPOSITES 40

FY 88 Accomplishments 41

Processing 42

Structure 46

Performance 51

POLYMER BLENDS ...................... 56

FY 88 Accomplishments. 56 . Experimental 57

Theory .......... ..... 60

SAXS and Pole Figure Facilities. 61

DENTAL AND MEDICAL MATERIALS ......... 63

FY 88 Accomplishments 63

Wear, Durability, Clinical Studies and Related Properties of Dental

Composites, Amalgams, Cements and Glass - Ionomer Cements 64

i
Medical Materials: Improved Tissue Adhesive and Improved Surgical

Bone Cement 66

Calcium Phosphate Chemistry, Biochemistry, Structure and Clinical

Implications 67

Dental Polymer, Composite, Cement, Sealant, and Adhesion Chemistry . 69

Dental Alloys, Ceramics, Metrology, and Analysis 70

OUTPUTS/INTERACTIONS 73

Publications ..................... 73

Technical and Professional Committees: Leadership Activities. ... 85

Industrial and Academic Interactions ................ 91

Associated Activities. ................. 96

ORGANIZATIONAL CHARTS. ................. . . 97

ii
INTRODUCTION

POLYMERS DIVISION

Leslie E. Smith, Chief

Bruno M. Fanconi , Deputy Chief

The Polymers Division is responsible for providing standards, measurement

methods, and fundamental concepts of polymer science to assist U. S. industries

that produce or use synthetic polymers in essential parts of their business.

This broad mission does not change markedly with time but the specific

technical programs within this broad mission must be continually assessed to

meet the industry's changing priorities.

This year marked the first year of funding for an expanded program in polymer

matrix composites. While these materials have been used for some time as high

performance laminates for the defense and aerospace industries, their use in a wider variety of civilian markets has been inhibited by several technical

factors. An important barrier is that the low volume lay-up processes used to

make very high performance aerospace parts cannot be easily adapted to higher

production volumes and lower part costs. The government investment in

fundamental research on polymer composites has been almost exclusively directed

toward the production and use of high performance laminates. There is a need

to provide a science base for composite processing methods that have broader

potential applications to civilian transportation, machinery, electronics, and

construction markets.

Based on the opinions of the participants in an industry workshop held at NIST

in October, 1987, we have planned a program to study the behavior of polymers

in transfer molding processes. Such processes inject a thermoplastic melt or a reacting thermoset mixture into a mold containing a fiber preform. Current

work on sensors described in this report will be joined during the coming year

by a modeling program which will describe the flow of polymer fluids under

process conditions.

A second barrier to the more widespread use of polymer composites is our

limited ability to measure and understand the way these materials perform or

fail in service. The highly anisotropic properties that allow composites to be

tailored for a specific application make their failure behavior very complex.

Composite properties are also highly dependent on their processing conditions.

This means that a meaningful composites program must integrate the mechanics of

composites with an understanding of the materials science of the polymer

matrix, the fibers, and the influence of process conditions. This is the goal

of the next phase of our program which we hope to expand in 1990.

Biodegradation has become a household word as many parts of the country try to

find solutions to the problem of municipal solid waste. Many states and

localities have begun to define materials in laws in advance of our technical

capability to measure or even agree on the meaning of terms. Recent federal

111
laws will require certain materials to be degradable under some conditions and

we see a need for standards and test methods in these areas . Several

scientists with experience in microbiology and in the analysis of degradation

products joined the Division this year. They will be exploring the technical

issues involved in measuring biodegradation and particularly trying to produce

reference materials that can standardize such measurements.

Technology transfer to industry continues to be a major concern of all of the

Division's programs. The most effective method is through direct interaction

with individuals from industry who know both their business and technical

needs. Many of these interactions come through scientists who collaborate with

us on technical projects. Last year the Division cooperated with 52 Research

Associates and 82 Guest Scientists who together spent 50 staff years of effort

at our laboratories. In addition, many industrial scientists have spent one or

two days using specialized equipment developed by Division scientists to

explore future research collaboration or to make proprietary measurements on

their developmental materials.

The Division's programs are described in this report, organized according to

these six Groups:

ELECTRICAL PROPERTIES

CHEMICAL PERFORMANCE AND STANDARDS

MECHANICAL PERFORMANCE

POLYMER COMPOSITES

POLYMER BLENDS

DENTAL AND MEDICAL MATERIALS

These Groups have made a number of significant accomplishments during the last

year. Some of these are summarized below along with references to the pages of

the report where more information about the work may be found.

• In the design of polymers for nonlinear optics, diacetylene

monomers which undergo multiple transitions to liquid crystalline

states prior to melting have been synthesized. Thermally activated

polymerization has been shown to occur not only in the solid state

but also within the liquid crystalline states, with an activation

energy of only 40% of that in the solid state. Furthermore, the

resulting orange-colored polymer retains much of the long-range

order present in the liquid-crystal precursor. (page 8)

• Certification measurements have been completed for a poly(methyl

methacrylate) Standard Reference Material, SRM 1487. Produced with

partial support from the Navy, this SRM will be used for quality

control of antifouling paints and as a calibrating material for the

analysis of acrylic polymers. Material has also been obtained and

work started on the first of two polyurethane Standard Reference

Materials, produced with partial support from the Food and Drug

Administration, which will help meet a growing need for better

methods of characterizing polyurethanes used in medical devices,

(page 13, 14)

iv
• A sensor has been designed to measure velocity, velocity gradients,

and flow instabilities. The sensor operation is based on

fluorescence recovery after photobleaching. A mathematical model

to describe its behavior has been formulated. (page 15)

• Significant removal of phosphorus from an industrial iron ore

concentrate by metabolic products of microorganisms was shown.

This treatment offers a potential method for upgrading domestic

iron ores that contain elevated levels of phosphorus to provide

higher quality raw material for steel making. (page 19)

• An off -resonance NMR method was developed which is most useful to

resolve methylene and methine resonances in rigid solids.

Separation of methine and methylene resonances is important in

cases where the chemical structures are not completely known or

where resonance assignments are required. (page 25)

• A constitutive equation has been developed which, for the first

time, describes the nonlinear mechanical response in a stress

relaxation experiment for a semi-crystalline polymer.. The

predictions of the new description are in good agreement with data

from a series of single and multistep stress-relaxation experiments

done in uniaxial extension on an ethylene -hexene copolymer. (page

31)

• An industry workshop on polymer composite processing was held with

attendees representing users, fabricators, and suppliers of

composites in the automotive, electronics, aerospace, and other

industries. The workshop identified the generic processing methods

likely to be of most interest to industry in the future and the

scientific and technical barriers that hinder the implementation

and effective use of these methods. (page 42)

• By varying the processing parameters, the molecular structure and

toughness of a model epoxy system were modified. For a given

composition, the toughness ,was found to correlate with the

compositional fluctuation measured by small angle x-ray scattering.

These compositional fluctuations can be controlled by changing the

processing parameters so that optimum toughness in the single phase

region can be obtained. (page 46)

• A new technique to measure the resistance of polymer resins to

interlaminar crack growth in their composites was developed. This

test uses a thin adhesive bond between metal adherents to simulate

the constraint on the resin deformation produced in the composite

by the fibers. Preliminary results shown an excellent correlation

between fracture energies obtained in the adhesive joint test and

experiments using composites. The new method has the advantages of

easy fabrication, small quantities of resin required, and no fiber

bridging problems. (page 51)

v
• A new procedure of obtaining the temperature, composition, and

molecular weight dependence of the free energy of mixing for

polymer blends has been established. This procedure which

integrates the experimentally obtained interaction parameter, x>

with theoretical calculations to obtain a parameterized free energy

function of mixing, has been demonstrated by using a binary polymer

blend of polystyrene/poly ( vinylme thy1 ether) . Spinodal and cloud

point curves have been generated and found to compare favorably

with experiment. (page 57)

• The use of crosslinks between unlike chains in a blend to increase

compatibility has been studied by a SANS technique. Blends of

polystyrene/poly (vinyImethylether) subject to radiation dosage of

125 MRad have shown an increase of the single phase region of over

250 e C. (page 58)

• In the study of spiro orthocarbonate monomers capable of

polymerization with an expansion in volume, a novel monomer was

prepared which exhibits reactivity comparable to conventional

methacrylate monomers and high ring-opening efficiency at near

ambient polymerization conditions. (page 69)

® A novel dental restorative, a hybrid cement - compos ite , has been

developed in order to overcome the propensity of conventional

glass -ionomer cements to brittle fracture during wear from

occlusion. The restorative involves the usual hardening of a

commercial glass ionomer cement along with the polymerization of a

water-soluble monomer (e.g. hydroxyethyl methacrylate) incorporated

in the system to provide toughening. In vitro tests revealed good

wear resistance, excellent oral -environmental resistance, and no

catastrophic failure during wear. (page 64)

vi
RESEARCH STAFF

Antonucci, Joseph M.

Barnes, John D.

Bauer , Barry , J

Blair, William R„

Blosser, Richard L.*

Bowen, Rafael L.*

Brauer, Gerhard M.*

Briber, Robert J.

Brinckman, Frederick E.

Broadhurst, Martin G.t

Brown, Walter E.*

^Research Associate

fGuest Scientist

o Synthetic and polymer chemistry

o Dental composites and cements

o Antioxidants

o Gas and vapor transport in polymers

o X-ray scattering

o Computer applications in polymer

measurements

o Polymer synthesis

o Neutron, x-ray and light scattering

o Ultratrace metals speciation

o Biotransformation of metals

o Polymer analysis by size exclusion

chromato graphy

o Environmental durability of coatings

o Adhesion measurements

o Adhesion

o Dental composites

o Biocompatibility

o Synthetic and polymer chemistry

o Dental composites and cements

o Adhesion

o Orthopedic materials

o Structure and morphology of polymers

o Electron microscopy

o X-ray scattering

o Environmental metal transport

o Organoraetallic chemistry

o Biological mediation of surface chemistry

o Ultratrace metal speciation and particle

biogenesis

o Molecular structure -activity relationship

o Dielectric measurement

o Piezoelectric and pyroelectric

modeling and theory

o Equation of state of polymers

o Ionic conduction

o Solution chemistry of calcium

phosphate (CAPH) compounds

o Biological CAPH compounds

o Atherosclerotic plaque

vii
Bur , Anthony J .

Carey, Clifton M.*

Chai, Herzl*

Chang, Shu Sing

Chiang, Martin

Chow, Laurence

Coyne , Laurence

Crissman, John M.

Davis, G . Thomas

DeReggi, Aime S.

^Research Associate

fGuest Scientist

o Dielectric properties of polymers

o Fluorescence monitoring of polymer

processing

o Piezoelectric, pyroelectric polymers

o Polymeric transducers

o Dental plaque

o Microanalytical analysis techniques

o Experimental Mechanics

o Mechanics of Adhesive Bonds

o Fracture o£ Composite Materials

o Thermal properties of polymeric

and composite materials

© Electronic packaging

o Polymer phase transitions

o Precision electrical and temperature

measurements

o Computational Mechanics (Finite Element

Analysis)

o Strength of Dental Systems

o Engineering Mechanics of Polymer Based

Materials

o Calcium phosphate compounds

o Dental and biomedical cements

o Solution chemistry

o Topical dental fluorides

o Molecular Deformation Mechanics in Epoxy

Networks

o Infrared Spectroscopy

o Neutron Scattering of Polymers

o Polymer Gelation

o Mechanical behavior

o Environmental stress -cracking

o Failure and fracture of polymers

o Piezoelectricity in polymers

o Polymer crystallization

o X-ray diffraction of polymers

o Polarization-depth profiles in

polymers

o Space charge in dielectrics

o Ferroelectric polymers

o Polymeric piezo- & pyroelectric devices

vxn
de Rijk, Waldemar G.

Dickens , Brian

Di Marzio, Edmund A.

Douglas, Jack F.

Duran, Randolph S.

Eanes, Edward D.*

Eichmiller, Frederick C.*

Eidelman, Naomi, N .

Fanconi, Bruno. M.

Fowler, Bruce 0.*

Giuseppetti, Anthony A.*

Gregory, Thomas M.*

^Research Associate

o Clinical dentistry

o Ceramic materials

o Expansion characteristics of solids

and semi- solids

o Weibull analysis

o Kinetics of thermal degradation

of polymers

o Photodegradation of poly (methyl

methacrylate)

o Curing of thermosetting resins

including printing inks

o Statistical mechanics of polymers

o Phase transitions

o Glasses

o Polymers at interfaces

o Theory on polymer solutions

o Polymer at interface

o Scaling and renormalization group calculation

o Polymer Liquid Crystals

o Physics of Polymer Glasses

o Structure of bones and teeth

o Calcium phosphate compounds

o Effects of biological molecules on

precipitation of calcium phosphates

o Liposome studies

o Clinical dentistry

o Composites

o Dentin adhesives

o Atherosclerotic plaque

o Infrared & Raman spectroscopy of polymers

o Structure of polymers

o Polymer fracture

o Process monitoring of polymer composites

o Laser Raman structural analysis of

calcium phosphates

o Casting of dental alloys

o Titanium alloys

o Calcium phosphate compounds

o Surface chemistry

ix
Guttman, Charles M. o Solution properties of polymers

o Size exclusion chromatography

o Diffusion of small molecules into

polymeric systems

o Semicrystalline polymer chain

configurations

o Kinetics of polymer crystal growth

Han, Charles C. o Polymer blends

o Polymer characterization

o Small angle neutron scattering

o Static and quasi-elastic light scattering

Haller, Arthur W.* o Chemical reactions, chemical analysis

Huns ton, Donald L. o Adhesion science and technology

o Fracture behavior of polymers

o Processing & failure behaviors of

polymer composites

o Flow behavior of dilute high polymer

solutions

o Macromolecule -small molecule binding

Jewett, Kenneth L. o Redox kinetics of heterogeneous systems

o Organometallic speciation

o Abiotic transformation of metal species

o Analysis of organic mixtures

Johnston, Allen, o Nuclear magnetic resonance

o Mossbauer studies

o Chemical adhesion

Khoury, Freddy A. o Crystallization, structure and

morphology of polymers

(including polymer blends)

o Analytical electron microscopy of

polymers

o Wide angle and small angle x-ray

diffraction

o Structure and mechanical property

relationships

Kim, Hongdoo o Polymer diffusion

o Forced Rayleigh Scattering

o Polyelectrolyte

o Polymer Blends

Kirkpatrick, Diana M.* o Adhesion

o Chemical analysis

Kotowski, Kristine S. o Synthesis of chromophore - labeled

polymers

-"Research Associate

X
Krueger, Susan T. o Macromolecular structure

o Small angle neutron and x-ray scattering

o Dynamic light scattering

o In-vivo characterization

o Organic and inorganic composite particles

Kryder, Samuel J. o Electronic circuit design & construction

o Electronic troubleshooting & repair

Lee , Andre o Infrared & fluorescence spectroscopy of

polymers

o Statistical physics of polymers

o Mechanical behavior

Lowry , Robert Eo Applications of fluorescence

spectroscopy to polymeric systems

o Synthesis of chromophore- labeled

polymers

Ly, Agnes M.* o Clinical dental assistant

o Adhesion measurements

Mathew, Mathai* o Crystallography

o Calcium phosphate compounds

Maurey, John R. o Ultracentrifugation

o Rayleigh light scattering

o Osmometry

o Dens ime try

o Refractometry

o Intrinsic viscosity

McKenna, Gregory B. o Nonlinear viscoelasticity

o Molecular rheology

o Physics of polymer glasses

o Rubber elasticity

McKinney, John E. o Tribology of dental composites,

cements and alloys

Misra, Dwarika N.* o Surface chemistry

o Adhesion

o Chemisorption

Mopsik, Frederick L. o Dielectric measurements and behavior

o Automated measurement design

o Computerized data analysis & programming

o Electrical properties of polymers

Muller, Robert* o Denture base materials

o Soft liners

^Research Associate

xi
Nakatani , Alan o Polymer blends and solution properties

under shear

o Small angle neutron scattering

o Phase behavior of polymer blends

Olson, Gregory J. o Metals biotransformation

o Bioprocessing industrial materials

o Epifluorescence microscopy imaging

o Surface modification and bioadhesion

Parks , Edwin J

.

o Macromolecular organometallic chemistry

o Metals imaging in coatings

o Biological transformation of carbohydrate

materials

o Archival preservation

Reneker, Darrell H. o Crystallographic defects in polymers

o Polymer structure

o Electron microscopy of polymers

o Vibrational spectroscopy of polymers

Roth, Steven C. o Piezoelectric polymer transducers - fabrication and applications

o Vacuum deposition of metals

o Calibration of polymer transducers

Rupp, Nelson W.* o Clinical dentistry

o Amalgams

o Direct golds

o Dental standards

o Composites

o Titanium castings

o Microleakage

o Dentin adhesives

Sakurai, Shinichi^ o Polymer blends

o Equilibrium and kinetics of phase separation

o Light scattering

Schen, Michael A. o Living polymer synthesis

o Polymers for non-linear optics

o Molecular electronics

Schreiber, Carol T„* o Topical dental fluorides

Sieck, Barbara* o Calcium phosphate compounds

o Chemical analysis

Smith, Leslie E. o Adsorption of polymers

o Polymer degradation reactions

^Research Associate

fGuest Scientist

xii
Stansbury, Jeffrey W.

Takagi, Shozo*

Takahashi, Yoshiaki*

Tesk, John A.

Tomazic, Branko*

Trout, Todd, K.

Tung , Ming , S .

VanderHart, David L.

Venz, Sabine*

Verdier, Peter, H.

Vogel, Gerald L.*

o Synthetic chemistry

o Polymers and polymer composites

o Polymerization expanding monomers

o Crystallography

o X-ray diffraction

o Calcium phosphate compounds

o Polymer Rheology

o Block copolymer

o Polymer synthesis and characterization

o Casting of alloys

o Strength of dental systems

o Thermal expansion & properties of

dental materials

o Finite element studies

o Porcelain-metal system

o Atherosclerotic plaque

o Biological calcium phosphate compounds

o Photoactive organometal- chelate chemistry

o Diffuse reflectance/microscopic epifluorescence

o Spectrophotometry

o Element-specific microscopic epifluorescence

o Biological solution chemistry of

calcium phosphate compounds

o Equilibrium studies

o Measurement of orientation in

polymer fibers and films

o Solid state NMR of polymers

o Measurement of polymer morphology

on the 1-10 ran scale

o Clinical dentistry

o Dental composites

o Dental polymers

o Polymer solution properties

o Polymer chain dynamics in solution

o Statistical analysis of data

o Error estimation

o Computer simulation of polymer

chain dynamics

o Dental plaque, biological solution

chemistry of calcium phosphates

o Micro analytical techniques

'^Research Associate

fGuest Scientist

xiii
Wang, Francis W. o Photophysics and photochemistry

of polymers

o Fluorescence spectroscopy

o Thermodynamic and frictional

properties of macromolecules

Waters trat, Richard M.* o Dental metallurgy

o Metallurgical phase diagrams

o Structure of alloy phases

Wu, Wen-li o Neutron and x-ray scattering

o Electron microscopy

o Mechanical behavior of polymers

and composites

Zapas , Louis J

.

o Continuum mechanics & Rheology

o Non-linear mechanical behavior

of polymers

o Static fatigue of plastics

o Finite elasticity (rubbers)

^Research Associate

xiv
ELECTRICAL PROPERTIES

The goal of the Electrical Properties Group is to carry out long-range research

involving the interaction of electric fields with polymers. Our results

provide the basis for new or improved measurements which will lead to higher

performance of polymers in existing or new applications or to entirely new

polymer systems. Examples of the interaction of electric fields with polymers

which are investigated in our program include measurement of dielectric

constant and loss, determination of charge or polarization distribution in

films, development and application of piezoelectricity and pyroelectricity in

polymers, ionic conduction in solid polymers, electro-optic measurements on

specially synthesized materials, and magnetic properties of superconducting

ceramic/polymer composites.

The measurement of dielectric constant and dielectric loss as a function of

frequency and temperature has long been used to probe the molecular motions in

polymers. Development of a time domain dielectric spectrometer at NIST has

extended the ability of these measurements to follow dielectric properties

which evolve with time, since data for a wide frequency range can be obtained

in an interval of time comparable to the reciprocal of the minimum frequency of

interest. Also, an automated system which measures dielectric constant and

loss at a series of fixed frequencies between 100 Hz and 10 9 Hz is being used

to infer DC conductivity of polymer systems where polarization becomes a problem.

The laser - induced thermal pulse technique for measuring charge and polarization

distribution in thin polymer films is extremely useful in a variety of

programs. Measurement of trapped charge and its effect on altering applied

electric fields in DC cable insulation has been studied; the distribution of

charge in polymer films used in space applications is being investigated, and

polarization distributions in multiple layered structures of vinylidene

fluoride - trif luoroethylene copolymers of different composition have been

measured. Use of the technique to measure the electric field - induced

alignment of polar molecules dissolved in a polymer matrix is being explored.

Experience and knowledge gained from our research into piezoelectric and

pyroelectric polymers continues to be applied to the development of transducers

for other agency needs. Also, we are frequently called upon for technical

information in this area by companies interested in developing applications for

these polymers. Commercial interest is growing in copolymers of vinylidene

fluoride with trifluoroethylene or tetrafluoroethylene because of ease in

processing for ferroelectric properties and the Curie temperature which varies

with composition. The variation of electrical properties with composition,

thermal history, and morphology in these polymers is being studied.

Highly conjugated polymers have been shown to exhibit many properties desirable

for use in nonlinear optics (NLO) . These include large third order electrooptic coefficients, picosecond response times, and resistance to laser damage

in the energy range of interest. Research within the group centers on

substituted diacetylene monomers which polymerize in the crystalline or liquid

crystalline phase. Goals of the research are to understand the molecular

architecture necessary for large nonlinear optical properties and to test the

1
feasibility of controlling the morphology of the usually intractable polymer

through the organization of the monomer phase before polarization. The

dissolution and subsequent electric field- alignment of NLO molecules in a

polymer matrix is also being investigated.

FY 88 Significant Accomplishments

• The ability to obtain dielectric data in the time domain which can be

transformed to encompass frequencies from 10

" 4 to 10A Hz has proven to be

useful for detecting changes in cable insulation which has been exposed

to heat and gamma radiation. This ability to follow the evolution of

dielectric properties which was reported previously for monitoring the

cure of thermosetting resins in composites is now being extended to

monitor the firing of ceramic powders

.

• In the design of polymers for nonlinear optics, diacetylene monomers

which undergo multiple transitions to liquid crystalline states prior to

- melting have been synthesized. Thermally activated polymerization has

been shown to occur not only in the solid state but also within the

liquid crystalline states, with an activation energy of only 40% of that

in the solid state. Furthermore, the resulting orange-colored polymer

retains much of the long-range order present in the liquid- crystal

precursor.

• Composites of YBa2 CU3 07 „ ^ superconducting powders dispersed in

polyvinyl idene fluoride have been prepared and shown to have the expected

diamagnetic properties essential to applications involving levitation at

temperatures below the critical temperature of 92K. The polymer matrix

provides processability at elevated temperatures, flexibility at room

temperature , and a chemically inert environment for the imbedded

particles

.

Automated Dielectric Measurements

F. I. Mopsik

The Time-Domain Spectrometer for measuring dielectric relaxation has been used

to examine a wide variety of problems. This instrument, which was developed at

NIST, carries out measurements in the frequency range from 10 kHz to 0.0001 Hz

by measuring the charge response of a dielectric to an applied voltage step for

times from 10ps to 3000 s and performing a numerical transform on the data.

The sensitivity, accuracy and extremely wide frequency range has led to the

commercialization of this instrument by IMASS , Inc. Hingham MA and the first

units have now been introduced to the market. Areas in which the instrument

has been used are described below.

Process Monitoring

Previous work has shown great promise for the use of dielectric loss

measurements to monitor the cure of epoxy resin systems used in the production

of composites. In particular, for amine and imidazole based resin systems, the

changes during cure were very large, easy to characterize, and comparable to

2
other techniques used to study the evolution of the cure. Of notable

significance was the ability not only to follow the gelation of the resin, but

also to follow the changes in the resin well past this point.

Epoxy resin systems are not the only type of resin being used. A peroxidecatalyzed styrene resin system was measured to see how well a less conducting

system could be monitored. This is a short curing- time resin used in the

automotive industry. The results showed that this resin system also can be

easily followed even though the resin can self-heat to the point of thermal

runaway. This thermal runaway prevented a reliable comparison with mechanical

and DSC measurements but measurements of the self -generated temperature rise in

all the instruments involved indicated that the degrees of cure determined by

the methods are consistent.

In another application of process monitoring, in cooperation with the Office

for Nondestructive Evaluation and the Ceramics Division, the use of dielectric

relaxation data to study the processing of ceramics was begun. The first

studies were made on a yttria-stabilized zirconia ceramic as a function of

partial firing conditions. The data were evaluated for sensitivity to density

and possible grain boundary effects. In addition, the validity of impedance

spectroscopy using complex resistivity and its connection with the more common

presentation of data in the complex dielectric constant plane was started. The

first results on this particular ceramic did show promise and pointed out the

desirability of different forms of data presentation in these systems. However,

the great variability of the material parameters on composition precluded

further conclusions. A follow-up study for alumina based ceramics is planned

to expand on these results.

Reactor Cable Insulation Testing

In collaboration with the Electrotechnology Division under a contract with NRC

services have been provided to evaluate test methods for use in estimating the

life-time of cables used inside reactor confinement. Since dielectric loss can

be a monitor of the state of a dielectric, especially at low frequencies, the

use of the time-domain spectrometer and related techniques has been suggested.

Following previous results on cables obtained from the Shippingport reactor,

additional samples were obtained that had been exposed to a known dose of

25 Mrad from various sources. The insulation was all identified as crosslinked polyethylene but the samples clearly differed in terms of appearance and

additive content. All samples were measured in both the original, unirradiated

state and the irradiated state. A reference temperature of 50°C was maintained

for all measurements.

The materials in their untreated states varied quite extensively in their loss

over the measured frequency range of 10" 3 to 10 4 Hz. The filled samples all

had higher loss while the unfilled samples had extremely low loss. Upon

irradiation, the filled samples showed much smaller changes then the unfilled

ones. In particular, one of the filled samples showed virtually no change at

all while the unfilled ones showed very large values for radiation- induced

conductivity and signs of degradation. These results illustrate the great

3
sensitivity of radiation damage in polymers to additives and the need for

monitoring of actual cables.

Poling Mechanisms in Polyvinylidene Fluoride - Trifluoroethylene Copolymers

As part of a study to determine the mechanism for erratic poling behavior in

polyvinyl idene fluoride - trifluoroethylene copolymers, the dielectric loss

spectra for 70/30 and 80/20 composition copolymers was measured. This was done

to see if possible internal charge build-up was responsible for the behavior.

Since the dielectric properties of pure polyvinyl idene fluoride had already

been determined and poling characteristics were normal, it was felt that excess

charge carriers in the copolymer should be easily found.

All the copolymers showed similar behavior. Unlike the homopolymer no

relaxations centered at either 10 Hz or 0.1 Hz were found. The very low

frequency loss was quite similar to that of the homopolymer and did not change

with temperature in a manner consistent with conduction. No significant

correlation could be found with degree of difficulty of poling. Comparison

with poling experiments indicated that a charge mechanism was inconsistent with

the changes in poling behavior. Subsequent investigations have shown large

changes in coercive fields associated with initial crystallization conditions.

Plasticization

A guest worker from Johns Hopkins University is using the spectrometer to

measure the plasticization of polymers by gases by studying the shift in -the

relaxation spectra of the polymer. A compatible cell has been designed and

the first preliminary measurements carried out.

Thermal Pulse Measurements of Polarization and Space Charges

A. S. DeReggi, G. T. Davis, F. I. Mopsik, and S. C. Roth

Space Charge in Polymer Films

The distribution of electric charge or polarization across the thickness of

various polymers continues to be of interest within the Polymers Division and

in many other laboratories worldwide. The laser thermal pulse facility used at

NIST to determine polarization distributions has undergone evolutionary

developments to meet the specific requirements of changing tasks and to remain

state-of-the-art in the face of intensive work elsewhere on complementary

measurement methods using acoustical rather than thermal pulses.

Under the sponsorship of the Defense Nuclear Agency, NIST has assisted Hy-Tech,

Inc. of Radford, VA in clarifying the charging behavior of 8 /zm- thick Kapton

films. These films are used by Hy-Tech in simulating the electrical behavior

of many polymers used as structural components of spacecraft. Polymers

gradually charge up in a space environment (due to charged particles in Van

Allen belts, or cosmic rays) and can suddenly discharge with deleterious

effects on the spacecraft function if exposed to the X-ray-rich electromagnetic

pulse (EMP) produced by a nuclear event. EMP tests duplicating the conditions

in a nuclear event are difficult to run and are extremely costly (the available

4
National facilities to conduct such tests are few and all operate at very low

repetition rates of at most a few pulses per day) . There is interest in

finding out if the electrical behavior of polymers can be simulated less

expensively by using electron beams for charging and UV-rich rather than X-ray

rich electromagnetic pulses for discharging. A considerable amount of

fundamental research is required to address the mission- oriented concerns of

the sponsor and contractors. Samples charged at Hy-Tech have been sent to NIST

for measurement using overnight mail to reduce the time between electron beam

exposure and measurement. The quantity of charge measured for fixed beam

conditions depends on the beam exposure time, on the voltage across the sample,

and on the time between exposure and measurement. The distribution of remanent

charge depends on beam energy, the effects of the irradiation on material

properties and on the charge transport kinetics. The measurements performed so

far using 45 kV electron beam energy, few nA/cm2 beam current, and a few hours

charging times indicate remanent charge in the tens of nC/cm2 which is easily

measured. However, our understanding of the mechanisms is still only

qualitative. One objective of the research is to correlate the behavior of the

charging current, which depends on the irradiation time and on the voltage

across the sample, with the remanent charge measured afterwards. A second

objective is to characterize the charge remanance time which depends on the

radiation- induced conductivity. A third objective is to measure the changes in

remanent charge induced by voltages applied during the post- irradiation period

of relatively high electrical conductivity.

Polarization in VF2 /TrFE Copolymers

The thermal pulse facility has also proven useful in characterizing the

electric polarization behavior of copolymers of vinylidene fluoride and

trifluoroethylene which depend in unexpected ways on the thermal treatment.

Specifically, moderate heating of a sample in a ferroelectrically soft state

renders it highly resistant to poling or to ferroelectric switching by an

applied electric field, while heating it above its C.urie temperature restores

softness to the ferroelectric state. We have demonstrated that this unique

behavior can be exploited in the fabrication of biomorphic actuators and of

novel, layered composite, ferroelectric memory devices. Layered composites with

two or three layers were prepared using layers of either of two possible

copolymer compositions which were chosen to have different and far apart Curie

temperatures. One composition was 80% VF2 -20% TrFE with a Curie temperature of

140°C. The other composition was 65% VF2 -35% TrFE with a Curie temperature of

80 0 C

Judicious choice of the sequence of electrical and thermal treatment of a particular layered composite produced a variety of polarization combinations

for the various layers. These combinations were effectively characterized by

measuring the polarization distribution across the composite using the thermal

pulse technique. In the case of a three- layer composite with the inner layer

having a high Tc and the outer layers having a low T c , the following

polarization states were produced. First, the entire composite was poled and

it was verified by thermal pulse measurements that the polarization was

nominally uniform (the same in magnitude and direction for each component

layer) . Second, the composite was heated to 100°C (which is between the two

Curie temperatures) . Thermal pulse measurements showed that only the inner

5
layer retained polarization, the outer layers having lost their original

polarization as a result of heating to 100°C. Finally, the composite was

reverse poled. Thermal pulse measurements confirmed that the outer layers had

reversed polarization relative to the original and showed also that the inner

layer had not switched but instead had retained its original polarization.

That and related experiments have cleared up the poling behavior of the

ferroelectric VF2 -TrFE copolymer. We have shown that one type of thermal

treatment is necessary for poling to nominal saturation polarization. Remanent

polarizations of 9 /xC/cm2 have been achieved for samples with 80% VF2 , 20% TrFE

which have unusually sharp hysteresis loops among ferroelectric polymers. We

have also shown that another type of thermal treatment increases the stability

against electric-field switching of the polarization of a poled sample. We

have demonstrated that bimorphs can be constructed using layered composites.

We anticipate that, by inducing specific combinations of polarization states in

a multilayer composite by appropriate electrical and thermal treatment

sequences, it will be possible to construct devices with novel transducer or

memory properties.

Ferroelectric Polymers

G. T. Davis', A. S. DeReggi, F. I. Mopsik, and S. C. Roth

Small Area Ultrasonic Probes

Since the initial NIST work on spot-poled piezoelectric polymer membrane

hydrophones a decade ago, such hydrophones have gained wide acceptance for

probing ultrasound fields. The main benefit of using a polymer as the

piezoelectric material in ultrasonic applications, notably in medical

diagnostics where the ultrasonic medium is water, a saline solution or living

tissue, is that the probe is nearly acoustically transparent and hence allows

probing the ultrasonic field without disturbing it significantly. The common

diagnostic frequencies for a long time have been in the low MHz range (3.5 MHz

commonly) but current imaging systems use somewhat higher frequencies (7.5 MHz

typically) and ophthalmic systems use still higher frequencies (10-15 MHz).

For the low MHz range, typical active diameters have been around 1 mm. The

trend for increasing operating frequencies, together for the desirability for

the active areas to be small compared to the ultrasonic wavelengths require

smaller active diameters. The American Institute for Ultrasound in Medicine,

and the ultrasonics industry through its representative bodies, the National

Electrical Manufacturers Association and the International Electrotechnical

Commission have published guidelines for choosing- the size of the active region

of ultrasonic probes. A reduction of the active diameter from 1 mm to 100 /xm

would represent a significant improvement for the industry.

In collaboration with the U.S. Food and Drug Administration, Center for Devices

and Radiological Health, the Polymers Division is investigating novel

techniques for spot-poling polymer membrane hydrophones. Needle-ball electrode

configurations have been used successfully to obtain active diameters in the

range 200-300 /xm for 12 /xm- thick polyvinyl idene fluoride. These diameters are

significantly larger than the diameter of the needle electrode suggesting that

fringing effects set an electrical lower limit to the achievable active

diameter. Related research on promising alternative materials, notably a

6
copolymer of vinylidene fluoride and trifluoroethylene suggests that further

reductions of the active diameter may be achievable using local thermal

treatments applied to the desired active area. This related research shows

that the coercive field (the ferroelectric switching field required to pole the

material or reverse its polarization) depends on the thermal treatment.

Annealing a small spot on a sheet previously quench-crystallized is expected to

result in the spot having a much smaller coercive field than the rest of the

sheet. Poling would occur selectively where the spot heating occurred.

Concurrently, promising methods of spot heating involve using a suitably

focussed pulsed laser beam.

Improvements in measurement techniques for characterizing the smaller active

areas are being sought. The trend toward increasing operating frequencies to

the range of 10 MHz will also require extending measurements of the acoustical

properties of ferroelectric polymers to this region.

High Power Generators

For specialized applications, the ferroelectric polymers offer systems capable

, of delivering small amounts of energy associated with changes in electrical

polarization at a high rate and hence can be made into potentially promising

high power generators. In collaboration with Chronos , Inc. the Polymers

Division is investigating means of rapidly heating ferroelectric polymers by

means of a pulsed laser to produce fast pyroelectric signals.

Initial experiments employed a dye dispersed throughout the polymer which

absorbed in the energy region of a pulsed dye laser. The pyroelectric response

combined with the loss of polarization at the Curie temperature over a time

scale of l,us results in power outputs of up to 45 GW/kg.

High Tc Superconductor -Low Tg Polymer Composites

A. S. DeReggi, G. T. Davis, C. K. Chiang1 and L. J. Swartzendruber2

•^Ceramics Division, NBS

^Metallurgy Division, NBS

In a number of magnetic applications of high T c superconductors, such as

levitation, electrical continuity throughout the material is not essential for

the function. In such applications, composite materials consisting of powdered

high Tc superconductors incorporated into a polymer binder may play an

important commercial role because of the processing advantages they share with

polymers. They can be extruded into ribbons and sheets or injection-molded

into a variety of complex three dimensional objects.

In collaboration with personnel in the Ceramics Division and Metallurgy

Division, we have succeeded in preparing stable composites using polymers with

the requisite thermal, mechanical, electrical properties and chemical

inertness. Current research is aimed at understanding the relationship between

the magnetic properties of the composite and those of its components. An

important issue being addressed is whether an effective composite magnetic

permeability between 0 and 1 (susceptibility between -1 and 0) can be defined

7
to allow magnetostatic calculations of magnetic fields inside composite shells.

The superconductivity composite in an applied magnetic field is modeled by an

assembly of fixed, aligned magnetic dipoles, where the separation between

dipoles is large compared to the superconductor grain dimensions. This model

is analogous to the Lorentz model in dielectrics and predicts a composite

permeability which varies nonlinearly with superconductor volume fraction.

Magnetic susceptibility and magnetization versus magnetic field measurements as

a function of temperature and superconductor fraction are being obtained. The

dependence on superconductor- fraction measured so far are consistent with the

predictions of the Lorentz model. However, the experimental errors in

calibrating the measurements due to the shape of the specimens do not rule out

other models.

Equipment has been procured to measure the shielding factor of the undiluted

superconductor and of composites as a function of superconductor fraction.

These measurements are expected to provide further clarification of the

validity of the Lorentz model for predicting the magnetic behavior of a

composite

.

Nonlinear Optical Properties of Polymers

M. A. Schen, N. Tsutsumi 1

, and G. T. Davis

1 Guest Scientist, Kyoto Institute of Technology

Liquid Crystalline Diacetylene Monomers and Polymers

Within recent years, small organic molecules and polymer systems that

incorporate delocalized ^-conjugated electrons have received much attention

because of their unique electronic properties. Much of this now centers around

the transient response of these materials to high electric field strengths such

as are associated with pulsed laser systems. From a technological viewpoint,

these materials form the basis for the rapidly developing integrated and

nonlinear optics industries. From a condensed matter physics viewpoint, these

materials allow the investigation of photo - induced structural changes arising

from exciton generation in one-dimensional conjugated structures.

As potential elements within nonlinear optical (NLO) devices, polydiacetylenes,

(PDA's) combine a large number of important primary and secondary properties

which include a large non-resonant, third order susceptibility, picosecond

scale switching times, phase matching, film flexibility, and large dielectric

constant to name a few. However, if NLO devices are to be fabricated, a larger

macroscopic susceptibility must be achieved either by improving the intrinsic

susceptibility, of the polymer or by increasing the density of conjugated

units

.

An approach to obtain large PDA films which is being pursued in our laboratory

involves the synthesis and polymerization of unique diacetylene monomers which

exhibit liquid crystalline (1c) phase behavior. This exploits a unique

characteristic of diacetylene polymerization chemistry, i.e. the need for

nanometer- scale organization of monomer for formation of high polymer to

8
occur. Traditionally this has been achieved by conducting polymerizations

within the monomer single crystal or in organized molecular monolayers such as

are obtained by Langmuir -Blodgett techniques. Starting with liquid crystalline

monomers, it is believed that single phase, macroscopic monomer phases leading

to polymer of high optical quality can be obtained.

Another important purpose of this research is to expand our understanding of

how nanometer- scale organization influences the polymerization of

polydiacetylenes. Specifically, both intermolecular spacing between adjacent

monomers and the angle of tilt of the monomer relative to the crystallographic

c-axis are proposed structural factors that determine polymerization. Liquid

crystals frequently exhibit polymorphism whereby each phase is characterized by

an ever decreasing level of molecular organization with increasing temperature.

Consequently, with a single liquid crystalline monomer, a variety of organized

monomer phases can be obtained and structure -dependent polymerization can be

examined. It is our belief that by understanding the latitude of molecular

disorder which can be accommodated within a polymerizable diacetylene monomer

lattice, greater flexibility is gained in molecular processing of the

resulting polymer as a nonlinear optical material.

A number of novel diacetylene monomers, some of which exhibit liquid crystal

phase behavior, have been synthesized within our laboratory. Broadly speaking,

these fall within two material classes:

• Class A: monomers which exhibit liquid crystalline phase behavior and

result in insoluble polymer, and

« Class B: monomers which do not exhibit liquid crystalline behavior but

upon polymerization, are expected to yield side-chain liquid

crystalline polymer architectures.

Within class A, the 1-0B0A, 1 , 6 -bis [N- (4-oxybenzylidene) -4-n-octylaniline ] - 2 , 4-

hexadiyne , monomer has been most thoroughly studied within the past year.

Elevated temperature small angle x-ray scattering (SAXS) studies in conjunction

with optical microscopy and differential scanning calorimetry (DSC) of the

monomer show at least two and perhaps three different mesophases of which two

are smectic. Within the crystal(T<133°C) and the smectic mesophases, SAXS data

indicate that the monomer is tilted relative to the layer line at approximately

30° . Analysis of the wide angle x-ray scattering is incomplete so assignment

of intermolecular d-spacings between diacetylene monomer units is still

pending

Kinetic measurements derived from DSC data following the thermal induced liquid

crystal phase (lep) polymerization of 1-0B0A indicate first order disappearance

of monomer over much of the polymerization. A thermal activation- energy , E a , for polymerization initiation of 155kJ/mol is found. This is much larger than

the 92 kJ/mol. energy of activation for thermally polymerized l,6-bis(4-

toluene sulfonate) - 2 , 4-hexadiyne monomer. Preliminary kinetic data obtained

within the crystal phase indicates a larger energy of activation, about 295

kJ/mol . Further experiments at lower temperatures are now being conducted.

Models derived by Baughman and Schmidt both predict a narrow range of

intermolecular distances between diacetylene groups and monomer angle within

9
the unit ceil for polymerization to take place. Kinetic data in conjunction

with x-ray structural data are being combined to determine whether these models

for diacetylene polymerizability in the crystal phase can be extended to

include the liquid crystal phase.

FTIR and elemental analysis of thermally polymerized 1-0B0A are consistent with

the theoretical structure. No chemical degradation of the benzylidene side

chains is seen after polymerization within the 1c phase as shown by the midinfrared region data. Micro elemental analysis shows the mole fraction of C,

H, N, and 0 agrees within 0.00%, 0.55%, 0.11%, and 0.02% respectively with

theoretical values for 149°C/8hr t vacuum polymerized polymer. Poly(l-OBOA) is

insoluble in common solvents and is deeply orange colored.

SAXS experiments during and after polymerization have demonstrated a number of

important points. With polymerization, the sharp small angle reflection

representative of the monomer {001} is seen to decrease and eventually

disappear. This is replaced by a broad, strong reflection whose Q-vector

increases with conversion. Consequently, poly(l-OBOA) obtained via a lep

polymerization is shown for the first time to exhibit a lamellar- like

micromorphology. Microscale sheet- like ordering is therefore conserved with

lep polymerization. Whereas the SAXS data for the monomer represents the layer

thickness, the data for the polymer represents the distance between polymer

chains or sheets.

Wide angle x-ray scattering experiments for determining the organization within

the individual polymer layers are being planned for this year. It may„be

envisioned that depending on the particular microphase within which the monomer

is first polymerized, either three dimensional anisotropic or two dimensional

isotropic structures may result.

Guest-Host Systems

Polymer films can be made to exhibit large second order electric field

coefficients by incorporating small molecules of large polarizability,

followed by preferential alignment in an electric field. Cooling below Tg

retains the molecular alignment in the case of amorphous polymers and large

internal electric fields resulting from preferentially aligned polar crystals

induces alignment in the case of semicrystalline ferroelectric polymers. In

addition to the useful second harmonic generating properties of such films,

changes in the UV/vis absorbance and shifts in the absorbance maximum can be

used . as probes for internal electric fields in the polymers. Our initial

studies have incorporated 2 -methyl, 4-nitro aniline or 4-dimethyl amino, 4'

nitro - stilbene in a vinylidene fluoride- trifluoroethylene copolymer containing

25 mole percent trif luoroethylene . Preliminary data imply internal electric

fields on the order of a few MV/cm which is consistent with previously

published data and the polarization to be expected from the copolymer crystals.

10
POLYMER STANDARDS AND CHEMICAL PERFORMANCE

The goal of this task is to produce standard reference materials (SRM's) for

the polymer industry; to develop measurement methods, data, and models for the

control of polymer processing; and to carry out long-range research on polymer

characterization and chemical performance properties of polymers.

Polymeric SRM's certified for molecular weight are needed by the polymer

industry to calibrate gel permeation chromatographs which are used routinely to

measure polymer molecular weights and molecular weight distributions. The

latter are the most important physical properties in determining a polymer's

processibility and its end-use properties.

The need for improved monitoring of polymer processing has escalated in recent

years because of the large demand and market for advanced polymer materials

which require tight controls in processing conditions over a broad range of

variables. To satisfy these new requirements, we are developing sensors based

on fluorescence spectroscopy to monitor process conditions at the molecular and

microscopic level. The. objective of our program is to utilize these new

measurement techniques in conjunction with processing models to predict and

control the materials properties and performance of the final product.

Improved techniques for polymer characterization and better understanding of

polymer solution properties are essential to the efficient production of

polymeric SRM's. Consequently, experimental and theoretical studies of

polymer-solution properties are actively pursued in this task.

Protective additives are needed for fabrication and long-term use of most

polymers. In use, these additives inevitably diffuse through the polymer to

some extent and may migrate out of the polymer entirely. The polymer is then

left with poorer properties or made more vulnerable to degradation and failure.

This is a major failure mode of polymers, and lifetime prediction methods

explicitly include the rates of additive diffusion along with the rates of the

inhibited and uninhibited degradation reactions. The number of commercially

usable polymer- additive combinations is too large to be considered efficiently

on a case-by-case basis. The emphasis in this task is, therefore, on the

development of general principles or models of diffusion that are applicable to

the widest range of generically important systems. In addition, knowledge of

the general principles which control diffusion through solid polymers is

important to the design and evaluation of improved additive systems.

A program has been initiated on bioprocessing and molecular characterization of

organometallic materials in this task, as a result of the transfer of personnel

to the Polymers Division. Investigations in this program involve the use of

microorganisms and their metabolic products for upgrading, synthesis, recovery

and degradation of materials, and the development of methods for monitoring

biotic transformations of a variety of substrates. In addition, in response to

the need identified by Congress, a new effort has been initiated to study

biodegradation mechanisms of polymers.

11
FY 88 Significant Accomplishments

• Two linear low density polyethylenes used in gas piping (one with, and

the other without pigment) have been issued as Standard Reference

Materials, with support from the Gas Research Institute and the Office of

Standard Reference Materials. Such standards will be useful not only to

the gas distribution and associated industries but also to the rest of

the scientific community.

• Certification measurements have been completed for a poly (methyl

methacrylate) Standard Reference Material, SRM 1487. Produced with

partial support from the Navy, this SRM will be used for quality control

of antifouling paints and as a calibrating material for the analysis of

acrylic polymers. Material has also been obtained and work started on

the first of two polyurethane Standard Reference Materials, produced with

partial support from the Food and Drug Administration, which will help

meet a growing need for better methods of characterizing polyurethane

used in medical devices

.

® A polymeric chromophore, which consists of polybutadiene labelled with

fluorescently active anthracene, has been synthesized and characterized.

Since its number average molecular weight, 12,000, is above the

entanglement molecular weight, this polymer can be used to monitor

polymeric behavior such as non-Newtonian viscosity and molecular

orientation.

• The results of mixing experiments, carried out using a fluorescence

microscope, give quantitative support to our hypothesis that fluorescence

can be used to monitor the quality of the mixture of a two component

compound

.

• A sensor has been designed to measure velocity, velocity gradient, and

flow instabilities. The sensor operation is based on fluorescence

recovery after photobleaching . A mathematical model to describe its

behavior has been formulated.

® Significant removal of phosphorus from an industrial iron ore concentrate

by metabolic products of microorganisms was shown. This treatment offers

a potential method for upgrading of domestic iron ore reserves with

elevated levels of phosphorus, providing higher quality raw material for

steel making.

® Methods were developed to characterize metal accumulation and metal

particle formation by microorganisms using small angle neutron and x-ray

scattering techniques. These methods provide non-destructive . techniques

for investigating factors affecting the rate of metal processing by

microorganisms

.

• The use of extremely thermophilic bacteria for coal desulfurization was

demonstrated in collaboration with the Johns Hopkins University and with

the support of the Electric Power Research Institute. These organisms,

12
by virtue of their rapid metabolic rates may offer new methods for coal

beneficiation and have provided information on the molecular forms of

sulfur in coals

• Microbiological films were shown to significantly accumulate tributyltin,

the active biocidal agent in many new antifouling coatings. This

information provides insights into the mechanism of antifouling activity

of these coatings and suggests that such coatings could be designed to

have very low biocide release rates, lessening their environmental

impact.

Standard Reference Materials

F. W. Wang, C. M. Guttman, P. H. Verdier, and J. R. Maurey

Development of Polyurethane Characterization Techniques and Standards

There is a growing need for better methods of characterizing the commercial

polyurethanes used in medical devices, both before use and after degradation

following implantation. Because of the wide variations in the compositions of

these block copolymer systems, the usual methods for determining molecular

weight distribution (MWD) are of limited applicability and are difficult to

interpret. With support from the Food and Drug Administration and the Office

of Standard Reference Materials, we are undertaking a program to produce two

polyurethane Standard Reference Materials (SRM's) and to develop improved

methods for characterizing these and other block copolymer systems.

We are producing two polyurethane SRM's with weight- average molecular weights

determined by ultracentrifugation, and with limiting viscosity numbers

determined under the conditions commonly used for the estimation of MWD by gel

permeation chromatography. These SRM's are not the usual commercial

polyurethanes, but rather are model compounds to which the usual techniques for

determining molecular weights of homopolymers can be applied. We are also

developing methods for estimating compositional variation in polyurethanes,

both for checking our own SRM's and for investigating the range of variation in

commercial polyurethanes. During FY 88 we have obtained material for the first

polyurethane SRM, and have begun measurements leading to its certification.

Characterization of Gas Research Institute Polyethylene

Polyethylene is widely used for piping in gas distribution systems. It has

been recognized lately that better coordination of research and development

activities facilitating comparison of techniques and test data would result if

a single well characterized resin were available to all research workers in the

gas distribution and associated industries. Such a resin should be available

from a single supplier over a number of years. As a result the Gas Research

Institute and OSRM are supporting work on the characterization of two "linear

low density" polyethylenes used in gas piping, one with pigment, the other

without. The unpigmented resin has been designated SRM 1496; the pigmented,

SRM 1497. This new type of polyethylene is considerably higher in molecular

weight than any of the polyethylene SRM's now available. Such a standard is

13
useful to the rest of the scientific community because there is a growing need

for higher molecular weight polyethylene standards.

The melt flow rate, a widely used measure of polymer processing properties, has

been measured for SRM 1496 and 1497 by ASTM method D1238-82 under three

standard test conditions. The value obtained under one of these, called the

melt index condition, has been certified. The other two melt flow rates are

given as supplementary information. Work required for the certification of the

limiting viscosity number of SRM 1496 in 1 , 2 , 4= trichlorobenzene at 130 °C has

been carried out. The molecular weight distribution of both materials has been

estimated from gel permeation chromatography and is given as supplemental

information on the certificate.

Poly(methyl methacrylate) Standard Reference Materials

Three poly(methyl methacrylate) polymers with molecular weights of

approximately 8,000, 30,000, and 120,000, which are designated SRM 1487, 1488,

and 1489 respectively have been produced. The number -average molecular weights

of SRM's 1488 and 1489 were previously determined by membrane osmometry, and

certificates have been issued for both these SRM ' s . Measurements of weightaverage molecular weight of SRM 1487 by ultracentrifugation have been

completed.

Polyolefin Melt Flow Rate Standards

Melt flow rate (or melt index) measurements are used in specification of

polymers in the polymer industry. NIST SRM's with certified melt flow rates

are used to check equipment stipulated by the ASTM D-1238 voluntary standard.

Current NBS polymer SRM's all have melt flow rates of less than 2 g/10 min.

Additional polyolefin standards are needed for melt flow rates higher than 2

g/10 min.

A polyethylene SRM with a melt flow rate of 5 to 7 g/10 min is currently in

production. This work is supported by 0SRM.

A polypropylene with a melt flow rate of about 12 g/10 min is being considered

for certification using ASTM Method D-1238 condition 230/1.2. The need for

this material has been established through consultation with the members of the

subcommittee of ASTM D-20 in charge of Method D-1238. Support for this work is

currently being negotiated with a group of polymer companies represented on the

ASTM subcommittee.

Ore Bioleaching Standards

More effective bioprocessing designs and improved strains of bacteria are

sought for commercial ore bioleaching. These developments are limited by lack

of understanding of the underlying mechanisms and the factors which limit the

rate of microbial ore dissolution. In particular, data intercomparison Is

difficult because standard materials and protocols for conducting ore

bioleaching assays do not exist. We are working with OSRM and ASTM to develop

standards for metal ore bioprocessing.

14
A source of domestic pyrite ore material suitable for bulk SRM or research

material production has been identified and tested. The material has been

shown to exhibit reproducible iron bioleaching rates following NIST -developed

test procedures. These novel OSRM- supported results provide critical data

necessary for a proposed FY 89 prototype SRM production and international

bioleaching measurement intercomparison with ASTM.

Polymer Processinz

A. J . Bur, F.W. Wang, A. Lee, T.K. Trout and J.H. Shibata1

^•University of Tennessee

Work during FY88 has focused on five areas: the design of experiments to

measure fluorescence anisotropy and non-Newtonian viscosity as a function of

shear rate; the chemical synthesis of a polymeric chromophore which is being

used in experiments to measure fluorescence anisotropy; the development of a

mathematical model to describe fluorescence recovery after photobleaching and

its relationship to velocity and flow characteristics; measuring the quality of

mixing of a two component material using a fluorescent microscope; and,

negotiating with industrial laboratories for the purpose of carrying out

collaborative research and developing programs to solve polymer processing

problems of mutual interest.

Fluorescence Anisotropy and Synthesis of a Polymeric Chromophore

Fluorescence anisotropy measurements are being carried out using two pieces of

equipment, a capillary flow apparatus and a Weissenberg rheometer. The

capillary flow apparatus is used in conjunction with a commercial fluorimeter

so that fluorescence and viscosity can be measured simultaneously. A capillary

is positioned vertically in the sample chamber of the fluorimeter and the shear

rate experienced by the specimen is controlled by adjusting the pressure

applied at the top of the capillary. We have recently completed optical

instrumentation of the Weissenberg rheometer and are using it to carry out

fluorescence and rheological measurements. The range of shear rates covered by

these instruments is approximately 10~ 2 to 10 2 s" 1

.

Fluorescence anisotropy measurements are being conducted on a low molecular

weight polybutadiene specimen doped with a polymeric chromophore. The

polymeric chromophore, which has been synthesized in our laboratory, consists

of polybutadiene tagged with f luorescently active anthracene so that the

anthracene is situated at the center of the polymer chain. Infrared and gel

permeation chromatography indicate that anthracene has been placed in the

central position of the polymer chain and that the resultant number average

molecular weight is approximately 12,000 as expected.

Our working hypothesis for the anisotropy experiments is that, for a non-Newtonian fluid, the fluorescence anisotropy increases (and the viscosity

decreases) with increasing shear rate, and that the underlying cause of this

effect is molecular orientation. The fluorescence anisotropy experiment is

designed to measure this molecular orientation. In our first experiments we

15
have tested the converse of this hypothesis, i.e., for a Newtonian fluid,

fluorescence anisotropy is constant (as is the viscosity) as a function of

shear rate. Low molecular weight polybutadiene, ^ = 2800, which was doped

with the tagged polybutadiene ( 10“ ^ molar concentration), was observed to be

Newtonian and to have constant anisotropy in the shear rate range 10 to 80 s' 1

. We conclude that, within the sensitivity of our measurement, molecular

orientation of the tagged polybutadiene does not occur in this low molecular

weight polybutadiene. Experiments using non-Newtonian polybutadiene, = 24,000, are now in progress.

Velocity and Flow Model

A sensor to measure velocity, velocity gradient, and wall slip near the wall of

a processing machine was designed and a mathematical model to describe its

behavior was formulated. The sensor operation is based on fluorescence

recovery after photobleaching. The design consists of an optical fiber which

is threaded through the wall of a processing machine and is flush with the

inside wall. Polymeric material containing a photobleachable dye flows passed

the end of the optical fiber and the fluorescence properties in a defined

region at the end of the fiber are observed. At a given instant in time, the

dye in the probed volume is photobleached by a short pulse of ultraviolet

radiation. As function of time, fluorescence intensity recovers as

fluorescently active material flows into the probed volume. In the model, we

analyze this fluorescence recovery and derive a functional form for intensity

versus time. From the equations, it is possible to distinguish between laminar

flow and wall slip and, in the case of laminar flow, to obtain values for

velocity and velocity gradient. Experiments to test this model will be carried

out in FY89.

Measurements of the Quality of Mixing

Previous experiments carried out in this laboratory demonstrated the

feasibility of using fluorescence intensity fluctuations to monitor the quality

of mix of a two component mixture. This mixture consisted of polybutadiene

doped with an active chromophore (coumarin 30) and 14 /im grain size aluminum

oxide. Using a laboratory size mixer, fluorescence measurements were made by

directing a laser light beam to the glass wall of the mixer and monitoring the

fluorescence from material as it passed through the probe volume of the laser

beam. We observed that fluctuations in fluorescence intensity decreased with

mixing time and became uniform with time at the end of mixing. Our hypothesis

is that fluorescence intensity will be constant with time when a uniform

spatial distribution of material occurs. While the initial experiments

established qualitative support for this hypothesis, we have also carried out a

quantitative study of mixing. The quantitative data are being obtained using a

fluorescent microscope to measure the near neighbor distance between particles

and the standard deviation of this distance as a function of mixing time,

fluorescence intensity fluctuations, and optical density. We have established

a correlation between fluorescence intensity and optical density over a range

of mixing conditions and a correlation between near neighbor distance and

fluorescence fluctuations.

16
Interactions with the Polymer Processing Industry

Considerable effort was exerted for the purpose of increasing the amount of

industrial interaction and participation in our polymer processing program. A

news release, which was issued from the NIST Public Relations Division,

generated over thirty responses from major polymer processing companies. We

have responded to each request and are in the process of active negotiation

with a half dozen companies concerning the establishment of research

associateships . Additional industrial contacts are being developed via the 1ST

Intelligent Materials Processing Workshop to be held on August 31, 1988.

Molecular Characterization

F. W. Wang, C. M. Guttman, A. J. Bur, P. H. Verdier, and R. E. Lowry

Characterization of Polyimide Polymers by Fluorescence Spectroscopy

Polyimide polymers are important in electronics and associated industries

because they have properties suitable for photoresists and thermally stable

insulators. In collaboration with scientists from AT&T, we have initiated a

project to monitor the formation of polyimide polymer from p-diaminobenzene and

3 , 4 , 3

'

, 4' -biphenyl- tetracarboxylic dianhydride. The formation of the polyimide

polymer from the poly(amide-acid) is accompanied by red shifts in the

excitation and emission spectra. Therefore, the formation of the polyimide

polymer can be monitored by measuring the increase in the fluorescence

intensity at 560 run when the sample is irradiated at 460 run.

We have synthesized the poly(amide-acid) polymer, deposited thin films of the

polymer on silicon wafers, and characterized the formation of polyimide in

these films by fluorescence spectroscopy. We are also using FTIR and mass

spectrometry to characterize the chemical changes that occur during thermal

treatment of these thin films.

Fluorescence Studies of Polymer Solutions

Fluorescence quenching of dilute solutions of polymers allows one to study the

shape of the polymeric chain in dilute solutions and the chain's interactions

with itself, with other chains, and with solvent. The chemistry of attaching

fluorescent and quenching groups to a polystyrene chain has been worked out and

chains with varying concentrations of fluorophores and quenchers have been

made. Preliminary experiments on the properties of single chains in solution

have been done. Currently theoretical studies using renormalization group and

scaling methods are being used to establish the relationship between the

fluorescence properties of isolated chains or two chains in solution and other

chain properties. Monte Carlo simulations of single chain and two chain

properties are being carried out to check the renormalization group and scaling

theories. Our long range plan is to study the interchain properties of the

polymer in more concentrated systems so we will be able to obtain properties of

polymers in blends.

17
Dynamics of Polymer Chains

The dynamical behavior of polymer chains is important to improving both

characterization and processibility of polymers. The principal methods used to

estimate molecular weight, in particular gel permeation chromatography, the

only method available at present for estimating the distribution in molecular

weight, are dynamical nonequilibrium experiments which depend in part upon the

relaxation of polymer chains in dilute solution. In its present state, the

theory of these systems does not allow the calculation of molecular weight

directly from measured quantities; a series of calibrants of known molecular

weight is required. Improvements in the theory could reduce or even remove the

need for calibrants, allowing the determination of molecular weight

distribution of polymers for which calibrants are not available.

The processibility and the final characteristics of both plastics and

elastomers depend in large part upon the relaxation behavior of the highpolymer chains of which these materials are primarily composed. More realistic

theoretical treatments of polymer melts and elastomers, which must start with

more realistic treatment of the dynamical behavior of the individual chains,

will lead to more efficient processing and better fabricated end products. A

major shortcoming of the present theory is its

inability to treat excluded

volume and chain entanglement effects in a realistic way. Present work is

aimed primarily at the study of these effects, using a combination of

analytical and computer simulation techniques. The simulation results provide

data on simple model systems and serve to guide the development of better

theoretical treatments.

Present efforts in this project are in two areas. The first of these is a

study of the effects of changing the chain move rules upon relaxation behavior,

in an attempt to resolve discrepancies between results obtained by different

groups using different model systems. The second is a series of studies of

size and knotting effects in systems of closed-ring chains. Although these are

primarily studies of equilibrium effects, dynamical models are needed to carry

them out for closed-ring systems. The results of this work may help to explain

anomalies found in experimental data on such systems.

Failure of Latex Barrier Films

The failure of latex barrier films is of both commercial and medical interest.

Regions with low local crosslink density may be expected to fail under certain

loading conditions. We are studying the change in the crosslinked density

across the film by measuring the change in local swelling using fluorescence

technique

.

The stress to failure of rubber is known to decrease dramatically as a result

of the addition of a small amount of swelling agent. The swelling behavior and

stress to failure of these barrier films after immersion in body fluid

simulants is being studied. The work on latex barrier films is being supported

by FDA

.

18
Bioprocessing

G.J. Olson, F.E. Brinckman, W.R. Blair K.L. Jewett, S. Krueger, E.J. Parks,

T.K. Trout, J.S. Thayer1

, R.M. Kelly2

, E.J. Tierney3

, G. Eng4

, F. Baldi 5

, B.

Worthy6

, and C. Felkner6

^University of Cincinnati

2 The Johns Hopkins University

3 University of Maryland

4 University of the District of Columbia

5 University of Siena, Italy

6 Technical Assessment Systems, Inc.

Work in this Subtask is investigating the use of microorganisms and their

metabolic products for upgrading, synthesis, recovery and degradation of

materials and in developing measurement methods and standards to better

understand mechanisms and rate limiting factors involved in these processes.

Steel Research Program

Microbiological metabolic' products are being evaluated as potential agents for

upgrading the quality of raw materials used in steelmaking including iron ore

and simulated steel scrap. Domestic reserves of iron ore often contain

elevated levels of phosphorus which causes brittleness in steel. Low cost

routes are sought to remove phosphorus in ore concentrates. However, to date

industry has not been successful in achieving effective low cost processes. We

isolated a phosphorus dissolving fungus and identified metabolic products

capable of solubilizing phosphorus minerals. Tests with U.S. industrial iron

ore concentrates showed the bioproducts, consisting of oxalic acid and other

organic acids, rapidly (<10 min) removed over 50% of phosphorus from the ore

and potentially offer a novel bioprocess for domestic iron ore benef iciation

More detailed evaluation of biological dephosphorization and potential on-site

scale-up testing with Cleveland Cliffs Iron Co. and Michigan Technological

University is planned.

Also under evaluation is the concept of using low energy routes for metal

reduction. We investigated novel pathways to metal reduction using

microbiological metabolites. Bioreduction of gold and other precious metals to

pure metallic microparticles by volatile metabolic products was demonstrated.

The reactions involve the production of methylated metabolites which react with

the metal ions in water to form methylmetal intermediates. These undergo

reductive demethylation , forming pure metal particles. The particles were

studied by electron microscopy-energy dispersive x-ray microanalysis for

morphology and purity. The work attracted an invitation from the Metallurgical

Society and the American Institute for Mining Engineering to present a talk on

the subject at the upcoming Symposium on Biotechnology in Minerals and Metals

Processing. Several platinum group metals and catalyst industrial firms have

indicated collaborative interest.

19
Bioprocessing of Metals: Mechanisms and Methods

The removal of metals from solution is an area in which biotechnology is also

making a contribution in waste clean-up and metal recovery. Applications to

date are limited to a very few metals. The bioaccumulation of gallium by

microbial cells and gallium binding by exocellular biogenic iron chelators, or

siderophores , was demonstrated as part of an Air Force -supported project to

develop novel processes for gallium recovery to assure domestic supplies of

this critical element. In recent years there has been little or no domestic Ga

production. Ga occurs with Al but its separation is difficult and costly. Our

research may provide new options for Ga recovery using the extraordinary

specificity of certain biomolecules. Center for Analytical Chemistry

scientists are collaborating in this research. They isolated and characterized

the bacterial siderophore and are studying its Ga binding properties by NMR.

Non-destructive neutron and x-ray scattering and microscopic methods were

developed to measure the bioaccumulation of metals. The application of small

angle neutron and x-ray scattering techniques to characterize metal particles

in and on living cells was successfully demonstrated, and conditions necessary

to conduct kinetic metal bioprocessing experiments were established. These

novel methods now permit investigation of the factors affecting metal particle

formation rates in microorganisms. Epifluorescence microscopic imaging (EMI)

methods in combination with fluorogenic ligands were used to demonstrate

bioaccumulation of yttrium by bacteria and aluminum by plant material. The

metal- fluorescent ligand complex permits detection of metals on surfaces with

spatial resolution. These demonstrations illustrate the potential of the

method for trace monitoring of metals bioprocessing. The work with plant

material has attracted the interest of USDA scientists who are studying plantaluminum toxicity and need a method to reveal sites of Al uptake.

Biotechnological processing of metals often employs microorganisms that posess

metal resistances, as such organisms often transform metals in potentially

useful ways (precipitation, redox reactions, volatilization). In particular,

metal detoxification by microorganisms may potentially be applied to the

treatment of toxic wastes. In collaboration with Prof. F. Baldi of the

University of Siena, Italy, we studied the mechanism of chromium (VI)

resistance in a chromium- res is tant yeast isolated from tannery wastes. We

showed that the mechanism of resistance was the exclusion of Cr from the cells.

We also characterized mercury resistance and biotransformations by aerobic

bacteria isolated from Italian cinnabar deposits. Hg resistance involved

reduction to volatile elemental mercury. We also showed that biomethylation of

mercury is not a mechanism of mercury resistance.

Bioprocessing for Upgrading of Fuels

The increasing concern over air pollution by combustion of fossil fuels has led

to increased research on methods for precombustion removal of sulfur from

coals. Better understanding of the molecular forms of sulfur in coal is needed

as are processes for removing organic sulfur. The desulfurization of coal by

extremely thermophilic bacteria (100 °C) was demonstrated in a joint NIST- Johns

Hopkins University project supported by the Electric Power Research Institute.

A novel approach using bioreduction, as opposed to oxidation, was taken as a

20
route of desulfurization. The extreme thermophiles showed extremely rapid

sulfur reduction rates. The use of microorganisms to bioassay sulfur species

in coal was also demonstrated. These data provide information on the types and

accessibilities of forms of sulfur in coal and also provide novel processing

options for coal beneficiation.

Biodegradation of Materials

The effects of microorganisms on the fate of materials in service environments

was investigated, including tributyltin-based antifouling coatings and

biodegradable polymers. Tributyltin (TBT) -based antifouling coatings are

effective in preventing hard (i.e. barnacles) fouling on ship hulls. However,

recent legislation in several states bans or restricts the use of ship

antifouling paints containing TBT biocide because TBT is toxic to non- target

marine life which may encounter the material after it leaches from ships and

drydock operations. Consequently, the development of effective antifouling

paints with TBT release rates as low as possible is sought. However, the exact

mechanism of TBT action on fouling organisms is not fully understood,

particularly in relation to the microbial biofilms which form on TBT-painted

surfaces immersed in seawater. We demonstrated the substantial bioaccumulation

of TBT in microbial biofilms composed of organisms obtained from test panels

coated with organotin antifouling coatings. There were no detectable

degradation products (di- and monobutyltin species) in the biofilms . or

surrounding solutions. These results provide the U.S. Navy with data

suggesting that the mechanism of antifouling action of tributyltin biocide may

involve its concentration in microbial films, resulting in repulsion of hard

fouling organisms (i.e. barnacles) from ship hulls. Consequently, antifouling

paints with very low biocide release rates may be effective in antifouling

protection while contributing minimal levels of toxicants to surrounding

waters

There has been rapidly increasing interest in the development of biodegradable

plastics to reduce environmental pollution, both in terrestrial and marine

environments. Definitions of biodegradability, and the associated measurement

methods and standards will be needed as new plastic materials enter the market.

Consequently, we acquired reportedly biodegradable starch-copolymer blends to

determine the kinds of organisms which degrade these materials, the products of

degradation and measurements which may ultimately be useful criteria for

biodegradability. Our studies in this area have only just begun. However, we

found that microorganisms specified for use in existing ASTM procedures for

measuring resistance of polymers to biodegradation will degrade certain of

these materials, as shown by their growth on the materials. Additional

research will be conducted in the coming year with support of OSRM.

New Measurements and Predictors of Toxicity

Microorganisms were investigated as agents for novel measurement methods for

ultratrace detection of toxicants and for validation of predicted toxicity of

molecules based on their molecular structural properties. In a recently

inaugurated collaboration with Technical Assessment Systems, Inc., their

research associates have installed and demonstrated with NIST staff members the

first applications of ultratrace biosensing of organometal toxicity by in vitro

21
computerized multilaser spectrophotometry. A battery of genetically defined

test microorganisms is evaluated for changes in morphology or growth upon

exposure to a toxicant, providing a diagnostic response "fingerprint". We are

correlating these responses with data obtained from conventional chemical

speciation measurements to determine the specificity and sensitivity of the

bioassay. The method may provide a more rapid, inexpensive, field portable

measurement system for a variety of compounds.

Biomolecular Characterization - Inorganic Materials

F. E. Brinckman, G.J. Olson, W.R‘. Blair, K.L. Jewett, E.J. Parks, T.K. Trout,

G. . Eng1

, E.J. Tierney2

, J.S. Thayer3

, H.E. Guard4

, andJ.M. Bellama5

1 IMSE Faculty Appointee, University of District of Columbia

2 Guest Scientist, University of Maryland

3 Guest Scientist, University of Cincinnati

4 Office of Naval Research

5 University of Maryland

Work in this subtask includes development of improved or novel methods

affording on-line or in- situ monitoring capability for inorganic,

organometallic , and non-metallic substrates undergoing biotic transformations

chemically and morphologically. Such characterization emphasis heavily relies

upon identifying key or diagnostic bioactive transient or intermediate

molecular species in important bioprocesses either supplying or appropriately

finishing industrially important materials. Moreover, since both design and

in-service performance of modem technological product materials may be subject

to environmental alterations invoked by biological agents, our work emphasizes

both isolation or production, as well as in-service durability. Key molecular

requirements therefore include uniform establishment of both element- and

molecular- specif ic detection capabilities at functional natural or

environmental in-vivo concentrations, typically ranging from parts -per-million

to parts -per- trillion for analyte elements.

In-Situ Element- or Molecule-Specific Microimaging of Bioactive Substrates

Reliable application of acceptable on-line biomolecular characterization suited

for materials bioprocessing must also avoid uncontrolled inhibition or

alteration of the key cellular activities and events delivering desirable and

designed biotransformations by either endo- or exo-cellular metabolisms.

Consequently, we place strong emphasis upon adapting acceptable non- invasive or

non-destructive bioprocess monitoring techniques.

We have successfully constructed and demonstrated applications of both

microscopic FTIR and EMI, respectively, for isolation of key metabolic pathways

rendering potential industrial mining application of fungal dephosphylation (as

orthophosphate bioproduct) of major iron ore supplies (FTIR), and bioextraction

or bioaccumulation of strategic or advanced technology metals such as yttrium

crucial to emerging superconductor industry or gallium essential to

semiconductor production.

22
Molecular Signatures and Recognition as Bioprocess Predictors

In collaboration with IMSE guest scientists, a complete NIST computer program

has been successfully demonstrated with capability to assess energetically

likely molecular configurations and van der Waals total surface area for

quantitative structure -activity relationships. We have demonstrated that total

surface area is a reliable predictor for both physicochemical and biological

properties, such as metal solubility, chromatographic partitioning, biouptake,

and toxicity.

Exocellular or Respirant Metabolic Bioprocess

In addition to our extensive effort for on-line substrate monitoring and

selection of optimal microbiological agents for inorganic materials

bioprocessing, we conduct intensive studies on the production of metabolites

excreted from cells that can induce or transform available source materials to

technologically significant isolated or finished products. Two prominent

demonstrations include the application of a globally abundant algal product,

methyl iodide, and another gaseous bacterial product, trimethyls tannane , issued

by a common aerobic estuarine heterotrope Isolated from the Chesapeake Bay.

In monitoring these exocellular bioprocesses, we also employ both gas and

liquid chromatographic separation schemes significantly enhanced by either

coupled atomic absorption or flame photometric detectors, affording direct

element- specific molecular characterization. Aqueous flow bioreactors

incorporating algal methyl iodide serve as effective solubilizing systems for

many metal ores and bulk metals, wherein the key mechanistic path involves

oxidative methylation of the metal or metalloid centers. Even with bulk iron,

a transient methyl- iron species forms which undergoes rapid protolysis to yield

methane (or CH3 D in D2 0) plus ferrous ion. In other bioreactions, we observed

similar transient methylmetal production by either the active carbonium ion

(from CH3 I) or carbanion (from (CH3 ) 3 SnH). In contrast, for precious metal

centers, including gold, platinum, palladium, and rhodium, a reductive

deme thy lation step occurs in presence of halide ions to yield pure

microcrystalline metal depositions.

23
MECHANICAL PERFORMANCE OF POLYMERS

The Mechanical Performance Group provides data, standards and concepts of the

mechanical properties of polymers, long term performance, and relationships

among structure, properties, performance and processing. Activities center on

characterization of mechanical behavior and solid state polymer structure.

Augmentation of methods to determine structure by scanning tunneling electron

microscopy (STM) has led to increased capabilities to elucidate structural

details at the molecular level by direct imaging. Information gained by STM

will bridge the gap between the size scales of conventional electron microscopy

and spectroscopic techniques. STM has been used in our laboratory to examine

graphite fibers as preliminary to the study of polymer structure at or near

graphite fibers.

The group continues a strong spectroscopic effort focussed on solid state NMR

and infrared spectroscopy. An NMR technique utilizing off -resonance proton

decoupling has been developed to delineate spectral features due to methylene

and methine carbons. Solid state NMR has also been applied to determinations

of the molecular conformation in polymer gels and intimacy of mixing in polymer

blends. The US Air Force Wright Patterson Materials laboratory and the US Army

Aberdeen Proving Grounds support work aimed at elucidating the structure of

polymer blends by NMR.

Mechanical properties and performance characterization and modeling has been

carried out on polymer glasses, gels, semi-crystalline polymers, and polymer

solutions. Parallel studies of the mechanical response and structure are

conducted to better understand structure-properties relationships in polymer

gels. Continuum mechanics treatments have focussed on descriptions of the

mechanical response of polymers subjected to multiple step deformations. A

constitutive relationship has been formulated which accounts for the

discrepancies between the observed creep and stress relaxation behavior and

that predicted from the BKZ theory.

FY 88 Significant Accomplishments

• The surface morphology of graphite fibers was examined by scanning

tunneling microscopy with a lateral resolution of better than lOnm. The

surfaces of the fibers was rough, with elongated asperities a few tens of

nm wide and a few hundred run long.

« An off -resonance NMR method was developed which is most useful to resolve

methylene and methine resonances in rigid solids. Separation of methine

and methylene resonances is important in cases where the chemical

structures are not completely known or where resonance assignments are

required

.

* A constitutive equation has been developed which, for the first time,

describes the nonlinear mechanical response in a stress relaxation

experiment for a semi -crystalline polymer. The predictions of the new

description are in good agreement with data from a series of single and

multistep stress - relaxation experiments done in uniaxial extension on an

ethylene -hexene copolymer.

24
Characterization of the Solid State Structure and Morphology

F. A. Khoury , D. H. Reneker, D. L. VanderHart, B. M. Fanconi , B. F. Howell 1

, &

E. Perez2

1 David Taylor Naval Laboratory, Annapolis, MD

2 Institute de Plasticos y Caucho, Madrid, Spain

Projects concerned with characterization of the solid state structure and

morphology of polymers focus on crystallizable polymers, polymer blends, and

polymers at the surface of graphite fibers. Details of the structure at the

molecular level were investigated with spectroscopic techniques and by

molecular modeling, while larger structural features were studied by electron

microscopy, optical microscopy and scanning tunneling electron microscopy.

Details of the single chain structure of isotactic polystyrene (iPS) prepared

from physical gels were clarified. Other studies were aimed at elucidating the

lamellar growth and proliferation processes which govern the progressive

evolution of spherulites from single crystal- like precursors in iPS

crystallized from the molten state. An investigation was initiated on

polyphenylene sulphide (PPS) , which is of interest as a high temperature

thermoplastic matrix material of carbon fiber composites. Current work on PPS

is described in the Processing and Reliability of Polymer Composites portion of

this report.

Model calculations are providing a view of the molecular architecture of chain

entanglements which provide the connections between polymer molecules that

yield the macroscopic mechanical properties observed in polymeric materials.

For example, ultra-high strength fibers of polyethylene are made by spinning a solution of entangled polymer molecules.

Solid state nuclear magnetic resonance (NMR) techniques have been used to

ascertain the degree of component mixing in polymer blends at the molecular to

tens of run range.

Morphology of Isotactic Polystyrene

In an previous study, it was shown that during the early stages of evolution of

iPS spherulites from the molten state pronounced inter lame liar splaying was

manifested in the initially formed multilayered precursor crystals.

Furthermore, this occurred prior to the development of any distinct

degeneration in the lateral growth habit of the lamellar layers from their

intrinsic hexagonal habit to an elongated but narrow lath- like ("fibrillar")

habit typical of the more advanced stages of formation of spherulites. The

question concerning the origins of the above mentioned occurrence of splaying

is whether or not it is mainly a consequence of the segregation of low

molecular weight and stereo- irregular chains between individual lamellae or

stacks of several lamellae. Exploratory experiments on the crystallization of

iPS from dilute solutions (e.g. 0.04% solutions of the polymer in 1:2 1-

chloronaphthalene/dodecanol solvent mixtures) , yielded interesting results in

this connection. Segregation effects would be expected to be minimal in

crystallization from dilute solutions. Yet, complex rosette- like multilayered

25
crystals in which the constituent lamellae exhibit splaying as well as curved

conformations akin to those in the melt-grown precursors of spherulites were

grown from dilute solutions. This similarity, revealed by scanning electron

microscopy, may be adduced as evidence that the splaying and curvature in the

melt-grown spherulite precursors are not mainly induced by segregation effects.

The formation, from dilute polymer solutions, of lamellar crystals which

exhibit variously curved conformations has been observed in other polymers. At

the root of an understanding of the origins of the curved conformations of

lamellae is knowledge of the interrelationships between curvature, the

sectored character of the chain- folded layers, and the incidence of screw

dislocations from which new layers are initiated. Resolution of these features

involves the use of transmission electron microscopy (TEM) , with the appendant

limitations on sample thickness. The above mentioned rosette -like multilayered

structures were too thick for this purpose.

In order to obtain detailed insights into the origins of the formation of

curved lamellae of iPS and the manifestation of interlamellar splaying under

conditions in which the effects, if any, of "impurity" segregation are

minimized we have undertaken a systematic study of the effects of

crystallization conditions on the habits of iPS crystals grown from dilute

solutions. Our objectives are: (a) To initially establish conditions in which

the polymer crystallizes in the form of six- sectored chain- folded monolayered

(and hence electron transparent) crystals, (b) To then systematically vary

temperature and/or concentration such as to favor more rapid crystallization,

which usually leads the formation of multisectored lamellae as well as to the

occurrence of a higher incidence of screw dislocations and the proliferation

therefrom of additional chain- folded layers, (c) To determine whether any

correlations can be established between the conformations (curvatures) of the

lamellae formed under different conditions, the extent to which the lamellae

are multisectored, the incidence of screw dislocations, and the occurrence of

interlamellar splaying. All these goals remain to be achieved. The crystals

grown under the conditions of crystallization which have been probed so far

have been multilayered. Examination in a scanning electron microscope revealed

that, as is the case in the above mentioned rosettes, their constituent

lamellae were curved. While differences in interlamellar splaying have been

observed, the species of crystals grown so far were, in the most, too thick for

examination with a transmission electron microscope. In some rare cases it was

possible to examine regions near the edges of crystals in transmission. It was

evident from the appearance of the lamellar texture in these regions that the

lamellae were multisectored, and that the proliferation of lamellar layers was

associated with a high incidence of screw dislocations. Detailed comparisons

between the fine structures of the various species of crystals have as yet not

been possible. On-going experiments in connection with electron microscopical

studies in transmission include attempts to isolate the multilayered crystals

from the polymer solutions at earlier stages of growth (and hence of chainfolded layer proliferation) than has been tried so far.

Ordered, Solid-State Forms of Isotactic Polystyrene

In work which grew out of a study of gels of isotactic Polystyrene (IPS) and

decalin (cis- or trans) , an important consideration was whether the iPS in the

26
solid phase of the gels constituted an ordered phase, e.g. a crystalline phase.

In the literature, it was suggested that iPS in the gel state adopted an

ordered structure having an 'extended chain' conformation. In fact, a 12 1 helical conformation was ascribed to the iPS chains instead of the usual 3 X helical conformation found in solution grown crystals of iPS or glassy iPS

samples annealed at temperatures above Tg

. The evidence for the 12 1 helical

structure in the gels usually came from observations on dried gels; so there

remained the question whether the original gels exhibited this same structure.

An 'extended chain' crystal structure is also ascribed to samples exposed to

certain solvent vapors, e.g. cyclooctane vapor. In this case, the vapor

generally produces some 3 1 helical crystals and some extended chain crystals,

the mixture depending on the temperature of solvent exposure. By implication,

these extended ’ chain crystals are related to the gel-state structure in iPS

gels. Since vapor- induced crystals could never be observed in samples

completely devoid of the original solvent, and since x-ray data for lateral

spacings in these extended chain crystal structures were sensitive to the

particular solvent used to produce the ordered structures, it was postulated

that there was probably solvent in the lattice of these extended- chain

structures.

13 C experiments were conducted in order to probe the similarity or

dissimilarity between the ordered states of iPS annealed glasses, iPS glasses

exposed to cyclooctane vapor, and iPs gels of trans-decalin (both original gels

and dried gels). 13 C spectra taken with cross-polarization and magic angle

spinning (CPMAS spectra) will yield spectra which are sensitive to the packing

geometry. Although a given spectrum cannot be interpreted in terms of a unique

chain packing, changes in lateral packing can be inferred from shifts in the

positions of spectral lines.

Results of this work which is still in progress are as follows:

a) The spectrum of the 3 X helical crystal has sharper and more numerous lines

than any of the other ordered states.

b) The spectrum of the cyclooctane-vapor- induced (CVI) crystals is different

from that of the 3

1 helical crystals. Particularly different are the positions

of the protonated aromatic carbon resonances. Indications are that the

aromatic rings in this structure are flipping by 180 degrees since the

linewidth and relaxation times associated with the para carbon are narrower and

longer, respectively, than for the ortho and meta carbons on the ring. It is

also significant that the unprotonated ring carbon is split into a doublet

indicating that this ordered structure has nonequivalent sites within the unit

cell associated with that carbon position. It is not at all clear that the

proposed crystal structure allows for such nonequivalence. It is likely that

the true crystal structure is more complicated than has been proposed. The

mobility exhibited by the aromatic rings at ambient temperature implies that

the CVI crystal structure is not as densely packed as the 3

X helical crystals.

In this context, the possibility that solvent exists within the crystal lattice

must be taken seriously.

27
c) The spectrum of the ordered structures within a dried gel is more difficult

to isolate than was the spectrum of the CVI crystals since 78% of the iPS

residues exhibit a glass -like spectrum. Nevertheless, the CPMAS spectrum of

the ordered regions of a dried gel, made from a gel of iPS and trans -decal in,

showed a spectrum different from either the CVI or the 3 1 helical crystals. In

particular, the aliphatic resonances were shifted upfield 1.5 - 2 ppm compared

to the other two crystal forms. Again, the protonated aromatic region did not

show very much multiplicity implying that there was some motional averaging of

the ring resonances occurring.

d) The CPMAS spectrum of a 25%iPS/75%trans-decalin gel gave indication of an

ordered structure, more ordered than the glass, yet less ordered than the

helical crystals. One of the unique features of the gel spectrum was the

upfield shift of the aliphatic resonances, compared to the same resonances for

the 3 X helical crystals, the CVI crystals, or the iPS glass. Thus, based

primarily on the similarity of the aliphatic resonances in the original gel and

the ordered regions of the dried gels, it is postulated that the dried gels

carry a memory of the ordered structures present in the original gels. Yet,

based on the spectra, this ordered structure is different from that of the CVI

or the 2 1 helical crystals. Perhaps a relevant point is that trans -decalin

will not promote vapor- induced crystallization.

e) The CVI crystal and the dried gel preparations each had residual solvent

which could not be removed by extensive vacuum pumping at ambient temperature.

The percentages by weight of solvent in these two preparations were about 15

and 10 respectively. Proton NMR showed that the solvent resonances in these

two preparations gave relatively narrow linewidths which, in turn, indicated

extensive motional averaging on the microsecond timescale. Therefore, if the

solvent is in the ordered phases, it must be quite mobile. An attempt was made

to ascertain, via proton spin diffusion (really polarization transfer) , whether

the solvent was in the CVI lattice. The interpretation of this experiment was

ambiguous since the initial polarization transfer occurred about equally

strongly to the disordered phase and to the CVI crystal phase. One possibility

consistent with experiment Is that the cyclooctane exists primarily at the CVI

crystal/amorphous interface. Another possibility is that the cyclooctane

exists both in the CVI crystalline phase and certain regions of the amorphous

phase. A model eliminated by these results is that the solvent is uniformly

distributed throughout only the amorphous phase.

Intimacy of Mixing in a Cross linked Blend of PEG/PMVT

In a continuation of work for the US Army Aberdeen Proving Grounds , we examined

the intimacy of mixing of a mixture whose proportions by weight were

0.6:3. 0:5.0 of diisocyanate crosslinking agent, IPDI, poly(ethyleneglycol)

,

PEG, having Mw = 1000, and poly (methylvinyltetrazole) , PMVT. The stoichiometry

is chosen so that the IPDI can react to completion with 90% of the hydroxy

termini of the PEG to form urethane - type crosslinks. The crosslinking is done

following a blending of all of the components. While the low MW PEG seems

compatible with the much higher MW PMVT in a blend of these two components

(only one T

g is observed) , there is a question whether any phase separation

occurs as a result of the MW increase of the PEG upon crosslinking. There is

28
also the question whether NMR can detect any specific interaction between the

PEG and PMVT chains, e.g. via chemical shift changes.

The NMR work undertaken this year involved taking CPMAS spectra at temperatures

below ambient. At temperatures around 240K the molecular motion is mostly

frozen out such that only very restricted motions take place. Under these

conditions, one can conduct proton spin diffusion measurements via the carbon

CPMAS spectra and interpret the results with reasonable confidence from the

known diffusion constant. The experiment involved producing a proton

polarization gradient between the PEG and PMVT protons and then observing the

gradient decay with time as a result of spin diffusion. It was found that we

could not. produce large polarization gradients; moreover, those that were

produced had vanished in 2 ms as a result of spin diffusion. Both of these

observations are consistent with intimate mixing in the sense that if the PEG

and PMVT tend to phase separate, their minimum domain dimensions have an upper

limit of 3 run. There was no direct spectral evidence for interaction between

the PEG and PMVT repeat units

Chemical Investigation of Thermally Polymerized Monomer Mixtures

We used our newly assembled 2.35T spectrometer to sort, via 13 C CPMAS NMR, the

chemistry associated with thermal polymerization of a bisbenzocyclobutene (BCB)

and a bismaleimide (BMI) . These materials were received as part of an Air

Force contract. Previous results were based on spectra obtained at 4.7T. The

higher field spectra have two characteristics which differ from the lower field

spectra. First, at our achievable spinning rates of 4 kHz or less, aromatic

sidebands at 4.7T always interfere with the aliphatic centerbands so that the

aliphatic resonance profiles cannot be isolated cleanly; at 2.35T this problem

does not occur. Second, carbons near to 14 N nuclei experience a residual

dipolar broadening which, in ppm, scales as B0

” 2 where BQ is the static

magnetic field. Therefore, at 4.7T, compared with 2.35T, the resonances of

those carbons bonded to nitrogens (both BMI and BCB possess nitrogens) becomes

as much as 4 times sharper. This field dependent broadening yields information

not available at a fixed field since the linewidth of a given carbon bonded to

such a nitrogen experiences other kinds of broadening also; moreover, the

amount of dipolar broadening at a given field is related to the magnitude of

the particular electric field gradient at the bonded 14 N nucleus. Thus, if a chemical reaction takes place close enough to a nitrogen to change its

electric field gradient, taking spectra at two fields will expose this change.

The results obtained previously were confirmed by the spectra at lower field.

In particular, the reaction of BCB and BMI does not produce an alternating

copolymer of BCB and BMI via a Diels -Alder addition. The new data also showed

that

a) The true aliphatic lineshapes deduced at higher field in the presence of the

aromatic sidebands were reasonably accurate.

b) Polymerization of BCB with itself, BMI with itself, or an equimolar mixture

of BCB and BMI always resulted in a substantial (the order of two- fold)

reduction in the 14 N quadrupolar coupling constants. This change is

reasonable in the case of the 14 N nuclei in BMI since the normal reactive site

29
is in the same five-membered ring as the nitrogen. For BCB, however, the most

reactive site is on a six- membered ring singly bonded to the nitrogen on an

adjoining five-membered ring. It is not expected that a chemical reaction at a

site so remote from the nitrogen should influence its quadrupolar interaction

so dramatically. Thus, the data suggest that ring-opening is occurring on the

five-membered ring containing the nitrogen. It is also clear from other

resonances that the cyclobutene ring, the primary site of expected reaction, is

indeed reacting to near-completion. Thus, while the chemistry is not

completely elucidated, it becomes clearer that BCB is undergoing some very

complex chemical reactions and that the products result from multiple,

competing pathways.

c) In BCB and equimolar mixtures of BCB and BMI the aliphatic carbon intensity,

relative to the total intensity, grows at a rate faster than expected upon

polymerization. This observation suggests that BCB is undergoing more

reactions than just the opening of the cyclobutene ring followed by addition

across a double bond. In fact, an increase in the fraction of aliphatic

carbons may suggest a reaction of double bonds with one another, as in the

polymerization of alkenes

.

Modeling of Entanglements Embedded in Polyethylene

Ultra-high strength fibers of polyethylene are made by spinning a solution of

entangled polyethylene molecules. The entanglements are incorporated into the

fiber, which may be highly crystalline. Models of entanglements which are

suitable as starting points for calculation of minimum energy conformations

were made. Rules similar to those that define crystallographic defects were

applied to create primitive entanglements that are completely embedded in a

polyethylene crystal. The entangled chains all approach their proper lattice

sites as they are followed away from the entanglement region. The most

primitive entanglements are linked, U-shaped chains with the stems that form

the "sides" of each U on adjacent rows of crystallographic sites. An example

is two linked chains with the two stems of one U running in one direction in a (110) plane with the two stems of the other entangled chain running in the

opposite direction in an intersecting {110} type plane. The chain stems in

this entanglement, plus the chains in two surrounding shells involve a total of

24 stems. The distortions of chains beyond the second shell appear to be

small. A model of this size can be adjusted to its minimum energy conformation

in a straightforward way with computers and software now available. A small

family of such primitive entanglements was defined. Such entanglement models

provide a basis for examination of the interactions between entanglements and

other crystallographic defects such as dispirations and dislocations which may

allow a chain to slide through the entanglement to produce the slow creep which

limits some applications of gel spun high strength fibers.

Scanning Tunneling Microscopy of Polymer Molecules and Carbon Fibers

Graphite fibers seven microns in diameter were positioned under the tip of a scanning tunneling microscope, using a specially constructed moveable stage and

related apparatus. The surface morphology of the graphite fibers (AS4) was

examined with a lateral resolution of better than 10 run. The surfaces of the

graphite were rough, with elongated asperities a few tens of nm wide and a few

30
hundred ran long. The scanning tunneling microscope provides an incisive method

for characterization of the surface morphology both at this scale and at the

atomic scale.

A review of progress in scanning tunneling microscopy applied to molecules and

carbon fibers was written. Reports of observations of DNA, small organic

molecules attached to carbon or metal surfaces, and changes in the shape (and

therefore the chemical structure) of small molecules resulting from the

application of a voltage pulse through the tunneling tip have appeared.

Polyoctadecylacrylate molecules were observed at the atomic scale on graphite

and other substrates. Parallel fibrils as small as 0.8 nm and triangular

structures consistent in scale with the side branches were observed. Voltage

pulses applied to the scanning tip modified and apparently cut through the

fibrils.

These sorts of observations which are beginning to appear in the literature

provide a basis for expecting to see the behavior of single polymer molecules

on the surface of a graphite fiber with the scanning tunneling microscope.

Such a capability would provide new information about the interactions between

the reinforcing fiber in an advanced composite and the matrix molecules, or

other molecules added to improve the behavior of the interface region.

A manuscript entitled "Morphology of Polymer Films and Single Molecules" which

summarizes our work on the use of the transmission electron microscope to

develop procedures for preparing polymer samples suitable for examination at

the molecular scale was prepared. A variety of methods used to prepare

dispersed single molecules and very thin films, some of which had network- like

regions with fibrils containing only a few molecules, are summarized. Staining

with Ru04 proved be a generally applicable way to observe structures at the

surface of a thin film on the scale of the molecular diameter. Structures

observed for different polymers were reproducible and characteristic of each

polymer

Measurement and Modeling of Mechanical Properties and Performance

J. M. Crissman, R. S. Duran, K. M. Flynn, G. B. McKenna, L. J. Zapas , A.

Brenna1

, Y. Chen2

, B. Coleman3

, and R. J. Gaylord4

1 Materials Department, Center for Industrial Research, Oslo, Norway

2 Institute of Chemistry, Academia Sinica, Peoples Republic of China

3 Department of Mechanics and Materials Science, Rutgers, The State University,

Piscataway, NJ

4 Department of Materials Science and Engineering, University of Illinois,

Urbana, II.

Reference Standard Polyethylene Resins and Piping Materials

Polyethylene currently accounts for approximately 80% of new natural gas

distribution piping in the United States. The Gas Research Institute has

sponsored a program at NIST to provide reference materials for use in research

related to natural gas distribution systems. This program has included the

procurement, characterization, and issuance of reference materials of a

31
pigmented and unpigmented pipe resin as well as piping and joints manufactured

from the pigmented resin. During the past year, work focussed on the

characterization of the melt flow rate properties and mechanical behavior of

material taken from the two types of T-joints for which preliminary work had

indicated a significant difference existed between the melt flow rates. The

melt flow rate has now been redetermined for material taken from several

locations within five different joints of each type. It was found that the

melt flow rate data for the two types of joints differ significantly from one

another and also differ from that of the resin. One of the* purposes of our

more recent work has been to determine whether the changes in melt flow rate

caused by the processing are accompanied by changes in the mechanical behavior.

Such changes may have relevance with respect to long term performance. Two

aspects of the mechanical behavior were examined. The environmental stress

crack resistance (ESCR) of material taken from both types of joints and the

starting resin was determined using a test method developed in our own

laboratory. The tests were carried out at 75 a G using an applied load of 5 MPa

and in the presence of a stress -cracking liquid. The increase in melt flow

rate observed for the butt fusion joint is accompanied by a decrease in ESCR,

whereas the decrease in melt flow rate found for the socket joint is

accompanied by an increased in ESCR.

Uniaxial creep experiments were also conducted on material remolded from the

two joints and the resin. In the region of largest strain, after the thinned

down portion of the specimen has propagated the entire gage length of the

specimen (necked and drawn material) , the creep curves plateau at which point

there is nearly a complete cessation of creep. In this region, the stretch

ratio X can vary from about 6 to 9 depending upon the level of applied stress.

For the specimens under the three highest loads it was found that the strain in

the plateau region is consistently slightly higher in the material from the

butt fusion joint than in that from the socket joint. This trend is consistent

with the behavior observed in other polyethylenes where it is found that the

higher the molecular weight is the less the maximum stretch is that can be

achieved under a given load prior to failure.

A more striking difference in behavior occurs for the three specimens under an

applied stress of 10 MPa. Up to a time of about 10 3 minutes all three

materials, including the specimen molded from the resin, show essentially the

same behavior. However, beyond 10 3 minutes the creep of the material from the

socket joint departs significantly in behavior from the other two. For

example, at the time at which the specimens from the butt fusion joint and the

resin exhibited neck formation (- 60% strain) the material from the socket

joint has only attained about one half the value of strain. The two specimens

under an applied stress of 9 MPa also appear to be showing the same

differences. However in this case several years may be required before the

difference in creep strain becomes comparable to the specimens at 10 MPa.

The results just cited indicate that the changes in melt flow rate brought

about by the processing are accompanied by measurable differences in the long

term mechanical behavior. The results suggest that in the socket joint

sufficient crosslinking and/or long chain branching occurred during the

processing to result in an apparent increase in the molecular weight and/or

molecular weight distribution. On the other hand, in the butt fusion joint

32
some slight amount of degradation may have occurred. It remains to be

determined to what extent these changes may affect long term performance under

normal use conditions. One phenomenon of concern to the gas industry is that

of slow crack growth in piping materials. The differences observed here may

well have relevance to this process. Further work is needed to better define

and understand the molecular and/or morphological changes taking place which

involve very long relaxation times, and the way in which these processes may

lead to instabilities such as those that lead to neck formation or stress -crack

failure

On the Multistep Stress -Relaxation Behavior in Uniaxial Extension of an

Ethylene -Hexene Copolymer

For crystallizable polymers such as polyethylene it is found that the

mechanical response in a stress relaxation experiment, even at quite small

deformations, is nonlinear and cannot be described quantitatively by the BKZ

theory. A better description of the behavior has been obtained using a new

constitutive equation proposed by Zapas . The predictions of both the BKZ

theory and the new description are shown for a series of single and multistep

stress -relaxation experiments done in uniaxial extension on an ethylene -hexene

copolymer of the type used in natural gas distribution piping. The results of

the calculations using the new description are encouraging and are in good

agreement with experiment. Also examined was a strain history involving a constant rate of strain experiment in which the strain was cycled up and down,

and a considerable degree of success was achieved in describing the observed

behavior using the same equation. To our knowledge this represents the first

time that a description of this particular type of strain history has been

successfully given for a nonlinear viscoelastic material. It appears that the

new formulation provides the necessary ingredients to describe quantitatively

the observed behavior.

Approximate Relations for the Analysis of Single Step Stress -Relaxation

Experiments in Uniaxial Extension

In a single step stress - relaxation experiment, a finite time is required to

apply the step in strain. As a result, some uncertainty is introduced into the

observed behavior at the early times during the experiment. Several years ago

an approximation was derived which can be applied to shear stress - relaxation

experiments when the deformations are small and the stress - strain behavior is

linear. We have extended this idea and have derived some approximate relations

which can be applied to measurements made in simple extension in the region

where the behavior is nonlinear. The derivation is based on the assumption

that, for the particular types of strain histories under consideration, the BKZ

theory can be used as a one dimensional description. In the new formulation

the stress a(e, t) at any time t after a step in strain e is given by

cr(e,t) =K(e,t-t 1 /2) (1)

K(c,t-t 1 /2) is the value of the stress -relaxation function at any time t after

a step in strain e, and t : is the time required to apply the step in strain.

ACe.t-tj./Z) is a correction term given by

33
A(€,t-ti/2)

2C

, . k (£/2 r

^

2

)]

l+e/2 L K (1+e , t-tx /2)

( 2 )

where C is a constant. In order to calculate A( e , t- t 1 /2) it is necessary to

determine K( e , tt

x /2) at two different levels of strain, namely e and e/2. As

the step in strain becomes smaller and smaller and the ratio t/tx becomes

larger ACejt-t^^/Z) approaches unity and equation (1) becomes equivalent to the

original approximation.

In order to demonstrate the validity and usefulness of the approximate

relations, we have obtained data on an ethylene -hexene copolymer at 26 °C. A

series of single step stress -relaxation experiments was done in which the

strain during the stress -relaxation portion of the experiment was 0.3%, 3%, and

6%, and the step time t x was varied from 0.1 s to as long as 100 s. For this

type of crystalline polymer it is found that the slope of the stress -relaxation

curve, when plotted on log- log paper, is linear and independent of the strain.

In this event the theory shows that only one experiment is needed in order to

obtain a good approximation to the nonlinear surface describing the single step

stress -relaxation behavior and the function K(A,t) can be represented by the

relation

K(A,t) = *( A)f« . (3)

By determining A(c,t-t1 /2) for different values of e and the ratio t/tx we were

able to correct the early time data to bring them into agreement with the

curves obtained from the experiments involving the shortest step time. The

procedures outlined should be particularly useful in instances where it may be

desirable to reach the predetermined strain via a slower ramp function, the

purpose being to avoid possible rapid heating or even fracture of the specimen

during application of the step in strain.

A Phenomenological Theory of the Influence of Strain History on the Rate of

isothermal Stress Relaxation

Constitutive relations were formulated for a class of incompressible

viscoelastic fluids for which internal structural changes occur at a rate that

is influenced by the history of the strain. For the materials considered, the

contribution to the stress at time t made by the strain at an earlier time r is

a function of that strain, the true elapsed time t-r, and a quantity 0(t,r)

that can be interpreted as the elapsed time measured by a clock whose rate of

advance, because it is tied to the rate of structural change, is affected by

the history of the strain. The functional relating 5©(t,r)/3t to the history

of the strain up to time t is assumed to have the same domain and a structure

similar to that relating stress to strain history. The present theory reduces

to the theory of BKZ fluids in the (extreme) special case in which 0(t,r) = tr, i.e., in which 3©(t,r)/8t si. It was shown that a constitutive relation

recently found to account well for observed discrepancies between experimental

observations and predictions of the BKZ theory can be considered first-order

approximation to the relations formulated.

34
Consider a body B in motion, and let £a (x,£) be the place in space at time 0 of

the material point P that is at x at time a. The value at P of the gradient of

the deformation taking the configuration at time a into the configuration at

time 0 is

Fa (^)=gradx Ca (x > )3)

This invertible tensor Fa {0) is called the deformation gradient (for P) at time

0 relative to time a. For the same material point, the left Cauchy-Green

tensor Ba (0) (at time 0 relative to time a) is the positive-definite symmetric

tensor given by

B„ (0)=^ (0)F„ (/J) 1

Making assumptions about the form of the quantity 8(t,r) which are consistent

with the principle of material indifference we obtained the following equation

SD (t)= P»(Br (t), t-r)dr

J - CO

+ P*(Br (C),t-r)r df dr + 0(e 2

) (1)

where SD (t) is the stress deviator.

With this equation we were able to describe two step stress relaxation

experiments in concentrated solutions of polyisobutylene and polystyrene in

ranges in which departures from the BKZ theory are large. An analysis, to be

published, of data recently obtained by Crissman and Zapas for multistep, low

strain, motions of bars of high-density polyethylene indicates that the

behavior in elongation of semicrystalline polymers also can be described by Eq

(1) in circumstances in which the BKZ theory does not hold.

The Free Energy Function of Crosslinked Rubbers

The mechanical response and the swelling response in crosslinked polymer

networks has generally been treated within the context of the Frenkel - FloryRehner (FFR) hypothesis, i.e., the free energy of mixing plus the elastic free

energy of the swollen rubber balance in swelling equilibrium. This is

generally written as:

-RT [In <l-v2 ) + v2 + * V] = Jh 3AA

(1)

A

2 d\

where R is the gas constant, T the absolute temperature, v2 the volume fraction

of rubber in the swollen state. x is the Flory-Huggins interaction parameter,

V1 is the molar volume of the solvent, A is the stretch and is equal to v2

" 1/3

, and AA is the elastic free energy per unit volume of dry rubber.

35
Importantly, in recent years the validity of equation 1 for crosslinked rubbers

has been questioned, yet the evidence has generally been based upon methods

which depend on the model used for AA or other assumptions, such as x being

independent of crosslink density. In the work which we have been performing

under this task, we have been able to show that if one accepts the validity of

the FFR hypothesis, then a universal relation results between the effective

Flory-Huggins interaction parameter and the crosslink density of the network.

This result has no model dependence for the elastic energy of the network and

depends only upon representing the free energy of mixing as the Flory-Huggins

equation suggests. The dependence of Xe ff on crosslink density can be

expressed as:

Xe £f " Xo

X0

av ( 2 )

where Xq depends upon the swelling solvent and a appears to be a constant which

is independent of solvent. v is the crosslink density.

The experiments carried out in this task include mechanical and swelling tests

on dicumyl peroxide crosslinked natural rubber. We have crosslinked the

rubbers with from 0.6 to 20 parts per hundred peroxide. Torsion experiments

are carried out in which the torque and normal force are measured as functions

of time and deformation. From these results the value of 8AA/8X in equation 1 can be calculated. Swelling has been carried out for each of the crosslink

density rubbers in a series of six solvents including good, poor and nonsolvent systems. The swelling results are used in the calculation of the

mixing free energy term in equation 1

.

In future work we will measure the elastic free energy derivative of the

rubbers in the swollen state and compare it with that determined from the dry

state measurements. In addition, experiments to examine the possibility that

equation 2 is a universal function in terms of some critical crosslink density,

v

*

, are being designed.

Relaxation of Crosslinked Networks: Theoretical Models and Apparent Power Law

Behavior

There have been several reports recently in which molecular models were

proposed to account for the relaxation behavior of crosslinked networks. All

of the models have been based upon the assumption that the long time relaxation

in networks is due to "dangling" chains that are attached to the network at

only one end. Importantly these theories predict that the relaxation of the

network in the terminal zone follows a power law in time, but differ in their

predictions of the power law exponent.

On the other hand, the experimental data generally cited in support of a power

law relaxation are taken from studies by Chasset and Thirion on dicumyl

peroxide crosslinked natural rubber. These data and other data by Plazek do

not support a power law relaxation function for crosslinked rubber.

36
We have reviewed the theories and the data relevant to the question of the

relaxation of network polymers. The data of Chasset and Thirion were

reanalyzed and it is shown that, while power law behavior is observed over a limited time range, the general behavior of networks is not well described by a

power law relaxation function. Rather, the important phenomenon of relaxation

in networks is the existence of a time-crosslink density superposition

principle. This is an experimental observation which cannot be explained by the

current theories of relaxation in networks.

Analysis of the Effects of Instrument Compliance on the Transient Normal Force

Response in Cone and Plate Viscometers

An analysis and series of experiments were performed to better understand the

transient normal force response in shearing experiments in the cone and plate

geometry. In our analysis we considered the response in single step stress

relaxation experiments. Results from experiments on a polyisobutylene solution

show deviations from unity of the ratio of the first normal stress difference

to the product of the shear stress times the shear strain. This ratio, which we

refer to here as U, is less than unity at short times and increases to values

greater than unity, possibly decreasing back towards unity at long times. The

so-called universal value of U is 1 from continuum mechanics.

The deviations of the response from the theoretical value can be accounted for

by including three important corrections in the analysis. First, the analysis

shows that the finite time required to apply the step introduces errors in the

normal stresses which are greater than those in the shear stress. This effect

would result in an apparent deviation from unity in the value of U even were a

machine of infinite stiffness used for the experiments. Second, the machine

compliance introduces errors in the normal force response by causing an

increased gap separation which subsequently relaxes as the normal force

relaxes. Third, the constrained geometry of the cone and plate results in the

compliance errors being "magnified" by some 1600 times, leading to the need for

large corrections and apparent violations of the universal relation at long

times

Experiments were carried out in tension and compression in a parrallel plate

geometry to demonstrate this effect in a viscoelastic fluid. It was found that

the variation in the magnification effect in this case is similar to that

observed in elastic bodies. This is the first time that such results were

demonstrated for a fluid body.

Dilatometry of Polymeric Glasses Subjected to Torsional Deformations

Work is continuing in the construction of a torsional dilatometer to be used in

the study of three important areas. First, measurements of the volume change of

solid polymers in torsional deformations will allow the determination of the

Wi, W2 , and W3 for the first time. (The Wi = 5W/3I 1 , where the I i

' s are the

invariants of the deformation tensor and W is the strain energy density

function) . Such measurements are important in the understanding of the

properties of solid polymers at large deformations.

37
Second, it is known that the volume of a glass changes spontaneously after a

quench from above its Tg to below it. The accompanying changes in mechanical

properties have come to be known as physical aging. In addition, it is observed

that the rate of physical aging is affected by the magnitude of the applied

stress or deformation. The resulting "rejuvenation", its interpretation, and

the mechanisms underlying it are quite controversial. An important parameter

in the controversy is the magnitude of the volume change which would accompany

the rejuvenation. In torsion the volume change due to the deformation itself

is of second order (vs first order in extension or compression) . Then the

measurements of volume change in controlled thermal and torsional histories

will permit the separation of the volume changes due to the mechanics, the

temperature and its history (aging) and any coupling between the mechanical

stimulus and the "free" volume of the glass. Such experiments will improve our

understanding of the glassy state and its response to mechanical stimuli.

Third, the effects of deformation on the glass transition are controversial.

Free volume models would predict virtually no change in T

g upon application of

a torsional deformation, whereas the Gibbs -DiMarzio model predicts a measurable

increase. We anticipate using the torsional dilatometer to test these

predictions

.

The dilatometer itself has reached a stage of development where preliminary

calibration measurements have commenced. Minor problems have developed and

these are currently being corrected in the shops division.

Predicting the Lifetime of Polyester Based Recording Media

An environmental aging study with the purpose of establishing the lifetimes of

magnetic tape, of the poly (ethylene terephthalate) base in photographic and

electrographic film, and of videotapes has been sponsored at NIST by the

National Archives. This project is now complete and the Final Report is in

preparation. The approach taken to estimate tape lifetime was to write digital

data on tapes, age them at specified temperatures and relative humidities, read

the data on the tape after aging, and alternate aging and reading attempts

until the tape became unreadable. The goal is to establish lifetime trends

which can be extrapolated to estimate a value under typical storage conditions.

Test methods were also developed to monitor tape status during storage. These

included: (1) the force required to peel binder from the support; (2) the

elongation of the tape at which the binder separated from the support; (3) the

number of rolling translations of a crease required to separate the binder from

the support; (4) the water content of the tape at. 45% relative humidity; and

(4) the change in weight of the tape during aging. It was found that all five

quantities changed significantly after aging, but did not consistently

correlate with tape lifetime, tape lifetime being defined as the ability to

read the digital data stored on the tape.

The aging results for PET indicate that the material should be quite stable at

ambient conditions provided that the process by which PET is made and the

rather specific combination of orientation and crystallinity now given the

polymer are not changed substantially. The combination of high temperature and

high relative humidity can cause rapid deterioration of the integrity of the

38
film base. The principal mechanism of degradation is hydrolysis. As few as

one chain scission per molecule is sufficient to cause serious loss in physical

properties

Both coated and uncoated electrographic film lost tensile strength and

elongation to binder separation faster than did the PET film base. This

observation might be used to advantage in the storage of magnetic tapes. Films

of this type , if stored under the same conditions along with archival

materials, should provide an early indication of impending failure.

Comparisons between the characteristics of video and magnetic computer tapes at

23°C revealed significant differences. The average peel force and elongation

for binder separation were 0.43 Newtons and 47% for the unaged video tapes,

whereas for the 'unaged computer tapes they were 2.6 Newtons and 108%.

Video tapes aged at 60°C and 75% RH showed a decrease in peel force and

elongation for binder separation of approximately 50% after 370 days of aging,

whereas the computer tapes, on average lost a much higher percentage of their

initial values after an even shorter aging period at 35 °C. The video tapes

showed only small decreases in peel force and elongation for binder separation

at 30% RH after 564 days of aging and about a 25% decrease in these quantities

at 75% RH. On the other hand, the computer tapes experienced larger decreases

in both quantities at both levels of relative humidity.

Rubber Standard Reference Materials

The Polymers Division maintains a series of Rubber and Rubber Compounding

ingredients as Standard Reference Materials (SRM) . These materials are used

widely by industry through ASTM standard test methods which specify the NIST

SRM's. During the past year the program was maintained through interactions

with industrial users - -normally testing of samples which the users identified

as defective, but which upon NIST retesting were within the original

specifications of the SRM. This interaction generally leads the industrial

users to reverify procedures of testing and equipment calibration. In

addition, SRM 384b (N- tertiary-butyl-2-benzthiazyl sulfenamide) was certified

as a rubber accelerator, thus renewing the stock of this material.

39
POLYMER COMPOSITES

One of the most rapidly growing areas in the materials field is polymer based

composites. Their high specific strength and stiffness combined with their

versatility in the manufacture of complex parts give them tremendous potential

for applications ranging from transportation to construction. For advanced

composites, growth rates of 16 percent per year and higher are frequently

cited. To maintain this growth rate, however, it will be necessary to overcome

major problems in two areas. First, there is a need to make processing more

rapid and reliable. Second, improvements must be made in our ability to

understand and predict performance, particularly long term durability.

To achieve these goals, the underlying science base, which is currently rather

weak, must be significantly strengthened. This is particularly critical now

since composites are moving beyond aerospace and DOD applications into

commercial areas such as automobiles, electronics, and construction. Advances

in these areas are critical to the international competitiveness of U.S.

industry. In response to this opportunity, the Composites Task is undergoing a

major expansion .facilitated by the Initiative on High Performance Composites

funded in 1988

.

The initial focus of this expansion will be processing since advances... in

processing science and implementation of on-line process control are the keys

to more rapid and reliable processing. In addition, current NIST programs on

the characterization of microstructure in composites will be strengthened to

compliment the processing studies. The final step in the program expansion

will be in the study ©f properties and performance. The emphasis will be on

establishing the processing- structure-property relationships that are needed to

improve our ability to understand and predict performance.

The following sections of this report describe the progress made toward these

goals during the last year. The efforts are grouped into three subtask areas:

Processing, Structure, and Performance. In the area of Processing, the

groundwork has been laid for the development of a processing facility. To

obtain industries' advice for this facility, a Workshop was held and 23

companies were represented. Efforts are underway to implement the two

processing methods that this workshop concluded were most important for the

future. A closer tie to the automobile industry has been established by

investigating resin systems with greater potential in that industry. Finally,

an other agency sponsored program has developed new, rapid-curing vehicles for

printing inks. The technology involved has relevance to the composites field

because many applications, such as composite repair, adhesive bonding, and high

speed composite fabrication, require materials with rapid and controlled cure..

The second subtask area seeks to bridge the gap between processing and

performance by developing techniques to characterize the structure of composite

systems. Both macro -structure (i.e. flaws, defects, phase separated domains,

etc.) and micro- structure (morphology, crystallinity, and the molecular network

of crosslinked systems) are of interest. During the past year the work on

multiphase toughened systems has continued and new programs on partially

crystalline thermoplastics and molecular composites have been added. In

40
addition, a project to investigate the role of precursor structure- in the

processing and performance of gel spun fibers has been initiated.

The third subtask focuses on the determination of performance properties of

composites and their constituents. Projects have addressed the failure

behavior of the resin (physical aging effects on fracture) , the fiber

(compressive strength), and the composites (laminate compression failure). In

addition, a new test method for determining a resin's resistance to

interlaminar fracture is under development. All of these projects relate to

delamination which is a major failure mode for laminated composites. Finally,

an other agency program is addressing data base development for composite

materials ..

To assist in these efforts, the Group utilized cooperative programs and guest

experts. The Institute wide Colloquium Series on Composite Materials brought

many world renowned scientists to NIST for discussions. Cooperative efforts

involved programs with the Departments of Treasury and Defense, and the

industrial research laboratory of Interez. Joint programs with Dr. A. J.

Kinloch at Imperial College (London), Dr. S. S. Wang at University of Illinois,

and Dr. John Gilmer of the University of Pennsylvania continue while new

programs with Dr. J. K. Stille of Colorado State University and Drs . Ron Eby

and Herzl Chai at Johns Hopkins have been initiated. As part of the last

mentioned program Dr. Herzl Chai is spending a substantial part of his time at

NBS. A research effort with the University of Massachusetts, Polaroid Corp .

and Kyoto Institute of Technology has been developed. Finally, Dr. Andre Lee,

a former postdoc at NIST, has joined the permanent staff, and Mr. Chung- Chien

Yu from Chun- Shan Institute of Science and Technology in Taiwan has worked at

NBS for the last 9 months as a guest scientist.

FY88 Significant Accomplishments

• An industry workshop on polymer composite processing was held at NIST,

and more than twenty companies were represented. Attendees included

users, manufacturers, and suppliers of composites in the automotive,

electronics, aerospace, and other industries. The workshop identified

the generic processing methods that will be of most interest to industry

in the future and the scientific and technical barriers that hinder the

implementation and effective use of these methods.

• A Small angle scattering (SAS) technique was applied successfully to

characterize molecular composites. By combining the neutron and x-ray

results, the scattering from voids, which in the past has made SAS

results difficult to analyze, can now be extracted. The first molecular

composite studied was a polyquinoline system, and the results indicated

that the rigid rod molecules are not dispersed at the molecular level.

• By varying the processing parameters, the molecular structure and

toughness of a model epoxy system were modified. For a given

composition, the toughness was found to correlate with the compositional

fluctuation measured by small angle x-ray scattering (SAXS) . These

compositional fluctuations can be controlled by changing the processing

41
parameters so that optimum toughness in the single phase region can be

obtained.

• A new technique to measure the resistance of polymer resins to

interlaminar crack growth in their composite was developed. This test

uses a thin adhesive bond between metal adherents to simulate the

constraint on the resin deformation produced in the composite by the

fibers. Preliminary results show an excellent correlation between

fracture energies obtained in the adhesive joint test and experiments

using composites. The new method has the advantages of easy fabrication,

small quantities of resin required, and no fiber bridging problems.

Processing

D. L. Hunston, S. S. Chang, W. -L. Wu, J. Ruff, K. Flynn, G. Bullman, F. I.

Mopsik, B. Dickens, B. J. Bauer, W. R. Blair and E. J. Parks

The Processing subtask included activities in three areas. The primary effort

focused on the preparation and implementation of plans for a composites

processing facility at NIST and the identification of the most critical

scientific and technical questions to be addressed with this facility. In

addition, projects were conducted to extend cure monitoring studies to a resin

system of interest to the automotive industry and to develop new ink vehicles

for air- drying and electron beam curing.

Industry Processing Workshop and the NIST Processing Facility

Composites rank near the top of the list of emerging technologies that are

vital to the international competitiveness of U.S. industries. Manufacturing

plays a critical role in the cost and reliability of these materials largely

because we lack the scientific understanding needed to improve efficiency and

implement on-line process control. The expertise and measurement capability

developed in the NIST Processing Task form the basis for an expanded program to

address these questions. A major step in this process is the construction of a processing facility with at least two different fabrication methods

represented. This facility will then be used to: (1) study processing in a realistic environment, (2) implement process monitoring techniques on-line, (3)

evaluate processing models, and (4) investigate on-line process control. The

facility will also be used to fabricate well controlled and characterized

samples for the Structure and Performance Sub tasks in the program.

Industry Workshop on Polymer Composites Processing

In developing this processing facility, industry input is critical to help

identify both the most important processing methods and the scientific and

technical barriers that the facility should be designed to address. In an

effort to get this input, an industry workshop on composite processing was held

at NIST on October 7, 1987, Through presentations by representatives of major

industrial sectors, a series of questionnaires, and discussion aimed at

achieving a consensus, the attendees ranked the most promising processing

42
methods and the most important scientific and technical barriers to effective

utilization of these methods. The time frame of interest was between 5 and 15

years from now.

The attendees represented 23 different companies including composite users,

suppliers, and fabricators. The industries included aerospace, automotive, and

electronics. The Workshop represented a highly diversified group with a

relatively balanced range of interests. In addition, comments were supplied by

a number of industrial people who could not attend, but expressed great

interest in the workshop.

The list of most promising processing methods included five techniques, two of

which were rated significantly higher than the rest: pressure molding and

transfer molding. Pressure molding includes both compression molding and

autoclave processing while transfer molding includes both reactive and

non-reactive materials. The three remaining processing methods were given

roughly equal ranking; they are thermo forming , filament winding, and

pultrusion. A major common feature for all five techniques is their potential

for development into rapid, cost effective production methods.

In addition to the five selected processing techniques, two technologies that

complement processing were also identified as very important. The first is

alternative sources of energy input to initiate or facilitate processing, e.g.

microwave, dielectric and ultrasonic sources or lasers. The other important

technology is the preparation of the resin- fiber starting materials, e.g.

powder processing for prepreg, commingled fibers, and resin coated fibers.

The workshop concluded that the most critical scientific and technical barriers

are deficiencies in our understanding of the chemical and physical changes that

occur during processing. Six areas were identified where the lack of knowledge

is most critical. The highest rated problem is the need to understand and

control resin flow and fiber orientation during processing. The second area is

modeling and control of temperature and heat flow. The concerns here ranged

from temperature levels and gradients during processing to the use of

alternative sources of energy input. Fiber-matrix adhesion is the third most

important area, while data validation, data base development, and standardized

tests ranked fourth. The control of morphology, such as crystallinity and

phase separation in two phase toughened systems, during processing was listed

next. Control of finish and dimensional tolerances is the final area

identified, which is of particular concern to the automotive and electronics

industries

In addition, the Workshop suggests that three classes of materials offer

significant potential for the future and should be watched closely:

thermoplastics, liquid crystal polymers, and molecular composites. The first

category is already included in much of the discussion above. The second and

third, however, are newer and other problems may emerge.

Plans for the NIST Processing Facility

Based on the results of this workshop and input from other sources, two

processing methods were selected for implementation in the first phase of the

43
program: autoclave molding and transfer molding. This means the two techniques

rated most highly by the workshop will be covered. The implementation of these

techniques is well underway and completion is expected within the next year.

The equipment is being designed with two considerations: (1) to maximize the

opportunities for on-line monitoring so the processing events can be studied to

gain a better understanding of the underlying science, and (2) to facilitate

the investigation and implementation of on-line process control. In this way,

the most important technical barriers identified by the workshop can be

addressed. In addition to these two processing methods, several other

techniques are under consideration as possible additions to the NIST processing

facility.

Curing Monitoring Applied to Automotive Resins

For a number of years NIST has had an active program to develop, maintain, and

correlate a wide variety of cure monitoring techniques. This program takes

advantage of NIST's capability in measurement science. There are currently ten

different process monitoring, methods available in the program, some with

on-line capabilities. These techniques can be grouped in terms of the

properties they measure: 1) mechanical and transport properties (viscosity,

dynamic mechanical, and ultrasonic shear wave measurements), 2) thermal

properties (differential scanning calorimetry, DSC), 3) electrical properties

(conductance and dielectric loss measurements) , 4) optical properties (various

types of spectroscopies, and fluorescence techniques), and 5) chemical and

structural properties (neutron scattering and size exclusion chromatography)

.

Many of these techniques and the associated research were described in detail

in last year's annual report.

During the past year, this capability was applied to study a vinyl ester resin

(VER) system of considerable interest to the automotive industry because of its

fast cure at relatively low temperatures and its reasonable cost. This system

involved a resin mixture composed of styrene and a vinyl ester resin with

propenoic esters on DGEBA backbone. A peroxide initiator at 1 part per hundred

parts of resin was used to cure the resin mixture. One factor hindering the

use of such resin systems is the lack of detailed information on cure kinetics

and practical data for cure behavior in realistic processing environments.

To address the question of cure kinetics, extensive DSC studies were performed

at a variety of cure temperatures. It was found that the VER system reached

more than 90% of full cure, even at temperatures as low as 60°C. The T , © however, was a strong function of cure temperature. By post- curing in the

temperature region of 120-150°C, a material with Tg around 113°C was always

obtained.

The DSC uses very small samples, and consequently, to investigate cure in a

more realistic geometry, both ultrasonic and dielectric measurements were used

to study samples cured at 90°C. With both techniques the observed cure rates

were much higher than for the corresponding DSC tests. In the ultrasonic test,

for example, the majority of the reaction occurred within one minute after a

short heat up period. One proposed explanation for this was that the

inherently low thermal conductivity of the resin prevented the heat generated

internally by the reactions from escaping fast enough to prevent overheating in

44
the center of the sample. The test specimens were 2 to 4 mm thick and 2 cm or

more long and wide. This overheating would cause a further acceleration of

the reactions producing more heat and perhaps a thermal runaway. To examine

this possibility thermocouples were placed in the dielectric and ultrasonic

samples. The results indicated that the internal temperatures reached values

30 to 40°C above the control temperature of 90°C. By contrast, the DSC samples

are small (-10 mg) and were cured in a sample container with a high thermal

conductivity. As a result, this effect was not present and estimates of

temperature overshoot were less than 2°C.

Both the ultrasonic and dielectric techniques have the potential for use in

realistic, even on-line, environments. The importance of this was observed in

the VER studies since sample size was a critical factor. In a practical

situation such . a thermal run could be beneficial since it reduces the cure

time. Modelling and characterization data such as that obtained here would be

essential, however, to prevent the internal temperatures from reaching the

point where thermal decomposition could occur. Future work will investigate

the effects of inert fillers, some of which will certainly change the thermal

conductivity. The sample size will clearly be a concern here as well.

Design and Synthesis of Intaglio Ink Resins

In another project NIST is developing new, rapidly curing material systems as

ink vehicles for intaglio printing processes at the Bureau of Engraving and

Printing. The objective is to achieve better control of the cure rate in

air-drying systems and in materials that can be cured with an electron beam.

The air- dry systems being developed are based on drying oil technology while

the electron beam curing materials use a free radical mechanism.

The performance requirements for the resins impose severe constraints. The

viscosity must be in the region of 100 to 500 poises, and the formulated inks,

containing the resins and pigments and other solids, must disperse in 1%

aqueous sodium hydroxide to which 1% w/w of surfactant has been added. In

addition, the resins must keep the various solid ingredients of the inks in

suspension.

The series of air-dry intaglio ink resins is based on molecules which are

similar to large drying oil molecules. A few alkyds have been included. The

drying oil- like molecules, based on polyhydric alcohols esterified with linseed

oil fatty acids, have satisfactory viscosity and cure. Dispersion in the

alkaline medium used to clean the printing press is highly dependent on the

formulation of the ink and on the acid number of the resins. A range of acid

numbers is being explored to provide resins with acceptable performance.

The series of resins which cure in electron beams is based on methacrylate

groups, which combine readily with the free radicals formed during exposure to

the electron beam. Methacrylates have been used rather than the faster-curing

acrylates to reduce the toxicity of the resin. An intaglio ink resin is

required to be a liquid. However, many methacrylates are solids. Also, the

resin has to contain enough methacrylates to cure rapidly and should have as

high a molecular weight as feasible. Reactions of a me thacrylate - containing

alcohol with various acid anhydrides give esters with one free acid group for

45
each ester group. Di-anhydrides give more than one isomer, which tends to make

the resultant resin liquid. These materials have more than enough acidity to

easily disperse the pigments and other solids in the ink and to disperse well

in the alkaline washing medium. Unfortunately, they are so viscous that they

must be diluted before they can be used as intaglio ink resins. Fortunately,

suitable water-dispersible, very low- viscosity, electron-beam active oligomers

are commercially available. Larger quantities of trial air-dry and electronbeam resins are being prepared for tests of toxicity, formulation, and

printing.

Structure

W. L. Wu, D. L. Huns ton, L. D. Coyne, F. A. Khoury, J. T. Hu1

, W. Su2

, J. K.

Stille3

, M. Shibayaina4

, S. Roy5, R. S. Stein6

1 Material Research Laboratories, Industrial Technology Research Institute,

Taiwan, ROC

2 The Shanghai Institute of Pharma and Technology, Shanghai, China

3 Dept. of Chemistry, Colorado State University, Fort Collins, Colorado

4 Kyoto Institute of Technology, Kyoto, Japan

5 Polaroid Corporation, Norwood, Massachusetts

6 Polymer Research Institute, University of Massachusetts, Amherst,

Massachusetts

The determination of molecular structure in thermoset resins is the major

thrust in the structure subtask of the composite research program. Both

neutron and x-ray scattering techniques were applied to investigate the

structure of resins based on di-functional and tetra- functional epoxies. The

processing- structure-properties relation of these resins has been explored. In

addition, research efforts have been extended to include both molecular

composites and a high strength/high modulus fiber forming material. Work has

also been initiated to study crystallization in partially crystalline

thermoplastics since these materials offer significant promise.

Processing- Structure-Properties Relation in Epoxies

One of the common schemes to enhance the toughness of epoxies is to increase

the molecular weight of the curing agents in order to decrease the crosslink

density. Unfortunately, the glass transition temperatures (T

g

) of the epoxy,

hence the use temperature of its composites may also be lower. It is desirable

therefore to keep the amount of high molecular weight curing agent to a minimum

while maintaining as much toughness as possible. Towards this goal, we

explored the possibility of enhancing the toughness by optimizing the

processing conditions for a given epoxy composition. The basic conjecture

pursued in this work is that the toughness of an epoxy formulation can be

improved by increasing compositional fluctuation on a micro scale. Based on

this conjecture, we modified the processing conditions to enhance the

compositional fluctuation. The structure of the epoxies cured under different

processing conditions was monitored with small angle x-ray scattering (SAXS)

.

46
Diglycidyl ether of bisphenol A (DGEBA) was the epoxy monomer used and

Jeffamine* D-230 was the curing agent. A high molecular weight version of D230 namely D-2000 was the toughness modifier. Both Jeffamines are linear diamine linked by polypropylene oxide chain. The molecular weight of these two

amines are 230 and 2000 respectively as designated in their names. The

formulation used throughout this work was 1:20:42 in mole ratio of D-2000 :D230: DGEBA. To change the distribution of the D-2000 di- amine from being

homogeneous to partially segregated, we adopted the following processing

scheme. The D-2000 di-amine (1 mol) was partially cured with DGEBA (2 mol) in

the first stage, followed by mixing with the rest of DGEBA and D-230. The

final mixture was then fully cured at 100°C for 24 hrs . It was found that

eight hours at 100°C was needed for the D-2000 (1)/DGEBA (2) to reach gelation.

Accordingly, the precure time for D-2000 and DGEBA was varied from 0 to 6

hours. The toughness was measured with precracked compact tensile test. T

g was measured with DSC. Scattering invariance (Ig A xs)’ an indictor for the

extent of compositional fluctuation, was calculated from SAXS data. The

results are listed as follows:

Processing- Structure -Properties of Epoxies

Precure Fracture Toughness Tg

( °K) AXS

time (hrs) (MN/m3 7 2

) 0 0.84 320 1.73

2 0.95 315 1.41

4 1.16 321 2.16

6 1.66 320 4.05

The sample with zero precure time was taken as the control. As shown in the

data above the compositional fluctuation correlated with the toughness. It is

also noteworthy that the value of T

g stays unchanged. Furthermore, there was

no indication of a second low temperature T

g corresponding to the separation of

the D-2000 phase.

In summary, this work demonstrates that the toughness can be increased without

lowering the T

g by optimizing the processing conditions. The relation between

compositional fluctuation and toughness observed in the present work needs to

be verified in other systems before being accepted as a general rule.

Small Angle Neutron Scattering of Precursors to Gel Spun Fibers

Polyvinyl alcohol fibers with high strength and modulus have been manufactured

via a reactive gel spinning process. The formation of alkaline gels is an

•essential intermediate step for this spinning process. The term "alkaline gel"

* Texaco Chemical Co. Certain commercial materials and equipment are

identified in this report in order to specify adequately the experimental

procedure. In no case does such identification imply recommendation or

endorsement by the National Institute of Standards and Technology, nor does it

imply necessarily the best available for the purpose.

47
refers to PVA aqueous solution containing borate ions at a pH higher than 10.0.

Without borate ions and high pH, the PVA aqueous solution will gel, but at a

much slower rate; the gels so formed are called hydrogel. The objective of

this work is to determine the change in PVA molecular conformation across the

sol-gel transition in alkaline gels. This transition is thermo -reversible and

rather well defined at a macroscopic level, e.g. by viscosity measurement.

Samples with different polymer molecular weight and concentration have been

studied using small angle neutron measurements (SANS) . The following

observations have been made:

1) The sol -gel transition is observed in SANS as a sudden change in the zero

angle intensity. The SANS transition however is about 20 °C higher than what is

observed via macroscopic measurements. This is consistent with what is known

in percolation theory as the finite size effect.

2) In the sol region, the correlation length is always greater than the radius

of gyration of the individual chain. This result suggests that the PVA

solution in the semi-dilute region is not homogeneous. Molecular clusters

persist at temperatures above the sol -gel transition.

(3) In solutions of polymer near the concentration C* where the chains start to

overlap one another, so-called critical behavior was observed near the sol/gel

transition. This critical behavior is manifested by a change in the

correlation length with temperature; the length reaches a maximum at the

sol/gel transition. Such behavior is absent for solutions with concentrations

greater than G*

.

Characterization of Polyquinoline Block Copolymer Using Small Angle Scattering

Techniques

Polyquinoline is a major candidate for molecular composites. In a molecular

composite, rigid rod molecules are dispersed in a matrix of a flexible polymer.

The molecular rods act as the reinforcing fiber. Molecular composites have the

potential to combine the performance of a composite, the easy processing of

thermoplastics, and excellent properties at high temperature. In the ultimate

molecular composite each molecular rod should be completely surrounded by

flexible polymer molecules. There is, however, a strong tendency for the rigid

rod molecules to aggregate and separate on a larger scale. To overcome this

problem a number of modifications to chemical compositions are being explored.

There is however a need to develop test methods to characterize the degree of

dispersion in these materials so progress can be quantified. The work here is

aimed at demonstrating that small angle scattering (SAS) is a viable technique

for the structure determination in the solid state. The presence of microvoids

has hampered the use of SAS for quantitative measurements of rigid rod polymers

systems and their blends. To circumvent this difficulty, both small angle

neutron and x-ray experiments were carried out on the same specimen. Due to

the differences in the scattering contrast factors of the voids between x-ray

and neutron scattering, the void contribution to the scattering intensity can

be determined and removed.

48
To evaluate this potential measurement method, a block copolymer of alternating

flexible segments of polyquinoline was studied. This is a promising system for

molecular composites since the block copolymer nature of the material may help

to promote good dispersion (the rigid and flexible segments substitute for the

rod and matrix molecules) . The average molecular weight for each block was

about 17,000. Based on the density values for the copolymer and the two

homopolymers, the following contrast factors for the scattering intensity I(q)

of the deuterated block copolymers can be obtained.

• IsAXs(q) = 9 - 23 V(q) + 3 - 37 x 10' 2 S(q) (1)

IsAHs(q> - 0. 855V(q) + 9.46 X l<r 2 S(q) (2)

where V(q) and S(q) are the structure factor of voids and block copolymers

respectively. The values of I(q) for both SAXS and SANS were reduced to the

absolute scale.

Both quantities are expressed in terms of the molar volume of the repeating

unit of the rigid rod segment, and its value is 6.995 x 10“ 22 cm3

. The

calculated molecular structure factor and the void scattering are given in

Figure 1. The abscissa of this figure is Q, the magnitude of a scattering

vector defined in its usual way; the ordinate is the form factor of the void

and the block copolymer in Fourier space. Based on the peak height of the

molecular structure factor, it is concluded that the block copolymer was not

phase segregated; however, a strong intermolecular correlation was observed for

each block. In other words, in the vicinity of a rigid chain the probability

of locating another rigid chain is greater than its volume fraction. The same

statement applies to the flexible chain also.

Crystallizable Thermoplastic Matrices for Composites

Thermoplastics offer important advantages as matrix resins for composites. The

toughness and processibility of thermoplastics are particularly attractive, but

some of these materials are also sensitive to attack by fluids. One approach

to solving this problem is the use of partially crystalline materials since the

crystallinity often improves resistance to fluid attack. To pursue this

approach, however, it is important to learn more about the crystallinity in

these resins and how it can be controlled. Poly (phenylene sulfide) (PPS),

whose melting temperature is about 300°C, is being used in initial studies to

address these questions.

The current and projected studies on the crystallization and morphology of PPS

fall into two main groups, namely: (i) Investigations of the basic fine

structural characteristics of the polymer, and their dependence on the

molecular parameters and crystallization conditions, and (ii) Investigations of

the influence of the carbon fibers on the crystallization behavior and

orientation characteristics in the PPS matrix due to enhanced nucleation,. if

any, at the polymer/fiber interfacial regions. The information derived from

part (i) of these studies is intended as background for determinations of

processing/structure and structure/property relationships of the PPS per se

while part (ii) addresses effects important in the composite.

49
Figure

1:

Form

(or

structure)

factor

for

voids

and

the

block

copolymer

plotted

against

the

magnitude

of

the

scattering

vector,

Q.

STRUCTURAL FACTOR

co

^

o o

o o o o

50
A focus in the current work is the study of the growth habits of single

crystals of this polymer with the object of determining the fundamental

characteristics of the process of chain folding. The unit cell of this polymer

is orthorhombic, and it is known that the b-axis is the preferred growth

direction in crystalline lamellae grown from solution, and in the constituent

lamellae of spherulites grown from the melt. Important details of the growth

and fine structure of the lamellae remain to be elucidated. Among these

details is the question of whether or not the apposition of chains in a folded

conformation occurs preferentially along specific crystallographic planes at

the lateral faces of the lamellae during growth, or whether these faces are

'rough' at the molecular level. The latter possibility would entail

crystallographically less specific folding and, In the extreme, the absence of

sectorization in the lamellae. These alternatives bear importantly on the

nature and extent' of disorder in the lamellae and hence on the physical

properties of the polymer; they are also basic to current debates concerning

the role of surface nucleation (secondary nucleation) in the kinetics of the

lateral growth of polymer crystals.

Experiments on the effects of melting conditions on the density of primary

nucleation in PPS crystallized from the molten state have established

conditions (melting at 300 °C, crystallization at 275-280 °C) under which

lamellar single crystals were grown in thin polymer films (i.e. in the range

10-100 run thick). A detailed transmission electron microscopical study of the

crystals is under way. The crystals are multilayered. The basal (leading)

lamella exhibits an overall lenticular lateral profile with an aspect ratio of

6-7. No distinguishable microfaceting could be resolved along the long and

seemingly curved edges of these lamellae, neither could any faceting be

distinguished at the extremities of their long axis. Dark field electron

microscopy and decoration techniques are being used to probe the fold domain

structure (sectored character) of the lamellae with the object of determining

whether or not chain- folding in these crystals occurs preferentially along

particular crystallographic planes. It should be emphasized in this latter

connection that previous studies of polyethylene crystals in this laboratory

and elsewhere have shown that the absence of crystallographically specific

lateral faceting in lamellae need not entail the absence of preferential

folding along certain planes.

Performance

D. L. Hunston, D. H. Reneker, Andre Lee, G. B. McKenna, H. Chai 1

, A. J.

Kinloch2

, S. S. Wang3

, R. K. Eby1

1 Dept. of Materials Science, Johns Hopkins University, Baltimore, MD

2 Imperial College of Science and Technology, London, England

3 Dept, of Theoretical and Applied Mechanics, University of Illinois, Urbana,

Illinois

The main thrusts of the research effort on mechanical performance was material

and structural aspects of damage tolerance. In the first phase, experiments

were carried out to elucidate the material aspects of failure (such as

fracture toughness and the effect of matrix ductility on damage zone

characteristics). Utilizing this information analytical models were developed

51
that predict the growth behavior of the flawed region. In particular, the

analysis shows how the failure stress can be increased by altering design

parameters such as fiber orientation, delamination size and shape, and fracture

toughness

.

Physical Aging of Epoxy Networks

Physical aging studies were performed using model epoxy network glasses.

Linear and nonlinear viscoelastic responses were measured after quenching the

glass from above Tg to the temperature of interest. In the linear viscoelastic

regime, the effects of crosslink density on physical aging were studied. The

stress relaxation curves at different aging times, temperatures, and crosslink

densities could be superimposed to form a single master curve, demonstrating

the validity o£ a time-aging time-crosslink density- temperature superposition

principle for this type of epoxy network. Furthermore, at temperatures of 10 °C

and 5°C below Tg , the network glasses could be aged into structural

equilibrium, thus obtaining, t* , the time required to reach structural

equilibrium. Results in the nonlinear viscoelastic regime showed that although

the aging- time shift rate decreased as the applied stress increased, t* did not

change with the applied stress level. Consequently, aging is not "erased” by

large mechanical stimuli. On the contrary, the results support the argument

that the volume recovery which occurs during aging impacts the small

deformation response differently than it does the large deformation response.

Effects of physical aging on the fracture toughness of epoxy network glasses

were also investigated. In the preliminary study, the fracture toughness

decreased as the time after a thermal quench, i.e. aging time, increases.

Currently the relative importance of crosslink density, degree of aging and

proximity to the glass transition in the fracture behavior of these network

glasses is being studied.

Compression Strength: Analysis of a Single Fiber

Recently, there has been a growing interest in the research and development of

organic fibers for use in advanced aerospace structures. A leading drawback of

current fiber products is their low compressive strength which, unlike

traditional glass or carbon fibers, is typically only a small fraction of their

tensile strength. Morphological studies suggest that this critically- reduced

strength arises from the peculiar structural makeup of the fiber. Such studies

show that the fibers are made of highly-oriented, fibril- like elements which

may- vary in size from a few nanometers (microfibril) down to perhaps the

molecular dimensions. Because these elements are only loosely held together

(either by secondary bonding forces or a network of discrete interconnections)

,

fiber disintegration can easily occur when interf ibrillar stresses are present.

A post-microbuckling analysis was developed to account for the low fiber

compressive strength. The analysis, based on a concerted microfibril buckling

induced by interf ibrillar shear stress, identifies the geometric and material

parameters responsible for fiber compression strength. Of these parameters,

microfibril thickness and interconnection distance, both of which are set

during fiber coagulation, figure prominently.

52
Interlaminar, Adhesive Bond, and Bulk Resin Fracture

An extensive experimental effort has been carried out to characterize the

energetic and morphological aspects of interlaminar crack growth in composites,

adhesive bonds, and bulk resin samples. Careful experimentation aimed at

elucidating the crack- tip damage zone characteristics was performed using tools

such as real-time movies or video recordings and post-mortem scanning electron

microscopy. The results helped to explain the similarities and differences in

fracture behavior for bulk resin, adhesive bonds, and composites.

Interlaminar fracture tests on composites are marred by a number of

complicating factors such as fiber-bridging- (the extension of fibers across the

crack opening behind the crack tip), interfacial (fiber/matrix) vs. cohesive

failure, and ’nonlinearity of the load-deflection curve due to matrix

plasticity. In addition, sample fabrication and testing are time consuming and

large amounts of resin are required, particularly when parametric studies (such

as temperature, moisture and rate effect) are of interest. To meet this

challenge, an alternative testing concept based on the fracture of thin

adhesive bonds is being developed. In this test, the resin matrix is

sandwiched between two metal adhe rends , with the bond thickness being similar

to the interlaminar spacing in laminated composites. Figure 2 shows a comparison between the mode I fracture toughness for the bonded joint and that

of the composite for three different resin systems: a brittle epoxy, toughened

epoxy, and a thermoplastic. Although the results are limited, the agreement is

excellent. The success in the mode I composite - adhesive joint correlation

has led to an extension of the work to mode II (forward shear) and mode III

(anti-plane shear) fracture components. Preliminary comparisons here are also

encouraging

Analysis of Laminate Compression Failure

Near- surface interlaminar defects, whether they are induced by foreign- obj ect

impact in structural composites or during fabrication in electronic circuit

boards, are very detrimental to compressive strength. Under such loading, the

(thin) delaminated layer buckles, causing intense stresses at the disbond

boundary which may lead to structural disintegration at loads well below the

design level. An analytical model was developed to predict the growth

conditions and growth behavior of the debonded region as a function of the

geometry and materials characteristics of the problem. The model assumes that

the delaminated region is elliptic in shape and separates a thick isotropic

plate from a thin orthotropic layer whose material axes coincide with the

ellipse axes. The growth conditions and growth behavior of this defect are

studied by separating the overall problem into an elastic stability problem and

a fracture problem. Post-buckling solution for the elliptic section was

obtained using a Rayleigh-Ritz type approach, with enough displacement terms

being incorporated to ensure convergence of all field quantities of interest.

The fracture problem was studied using a Griffith type energy balance criterion

based on a self-similar disbond growth. The analysis identifies explicitly the

role played by the experimentally determined interlaminar fracture toughness,

and points to novel means for increasing strength through variations in

stiffness properties of the delaminated layer.

53
COMPOSITE

INTERLAMINAR

G

IC

(J/m

CQ

CORRELATION BETWEEN METHODS

Figure 2: Comparison of adhesive and interlaminar frao- energies for three different matrix resins.
Draft Standards for the Identification of Polymer Matrix Composite Materials

and for Reporting of Test Results

Draft standards for the identification of polymer matrix composite materials

and for reporting of test results are being prepared in an effort supported by

the strategic defense initiative office (SDIO) , in cooperation with the ASTM

Committee E49 , the Military Handbook 17 project, and DOD contractors concerned

with data on advanced composite materials. The draft standards will be

available for use by ASTM and others. The following existing data bases for

advanced composites were examined in text form, discussed with their creators,

or studied by participation in meetings aimed at the design or improvement of

the database:

a. Prototype Advanced Materials Data Base User's Guide (PDA)

b. Data documentation requirements for MXL-DHBK-17

c. Guidelines and electronic data formats for reporting tensile

property data and test conditions for fiber reinforced polymer -matrix

composites per ASTM standard test method D3039 for fiber-resin

composites. (PDA)

d. Data on the thermal expansion of graphite -epoxy composite in

HTMIAC's high temperature materials properties data base.

e. Data on the ultimate tensile strength under rapid loading conditions

of graphite/epoxy composite in HTMIAC's high temperature materials

properties data base.

f. Format used by Martin Marietta Astronautics Group to present

materials property data on composite tubes and plates to the

Composite Materials and Applications Division of AMETEK.

g. Draft of SDS Spacecraft Materials Selection Guide for spacecraft

design engineers presented by AMETEK. This Guide contains

standardized tables of physical, mechanical and thermal data for

composite materials.

Examination of these data collection formats revealed many points of view, many

groups of data users, a complex set of interrelations, barriers to conceptually

simple interactions, and many other interesting facts.

Based on this it appears desirable to describe a comprehensive data base

containing all information about advanced composites, a facility for extracting

subsets of information that are of interest to identified groups of users , and

a number of specialized data bases, each to serve one of the identified user

groups. The draft standards are aimed at facilitating the collection and

smooth flow of information from where it is generated to where it is used, as

well as the evolution of the data bases themselves.

55
POLYMER BLENDS

The importance of the subject of polymer blends is self evident by its

ubiquitous presence in consumer products in resent years. These products range

from automobile and airplane parts, furniture, packaging materials, housewares,

toys to clothing materials.

Similar to metal alloys, polymer blends which are a mixture of two or more

polymers form plastic alloys with new properties. Many important material

properties such as the mechanical properties, flame retardance, processability,

barrier properties, etc. can be improved through blending. Also, in many

cases, high cost engineering plastics with special properties can be obtained

by the blending of low cost polymers. Several techniques are commonly used in

the blending (of alloying) of polymers: (1) Single phase materials formed by

using miscible polymer pairs; (2) phase separated morphology and structure

obtained through chemically bonded block copolymers; (3) phase separated

morphology obtained through compatibilization by crosslinking and grafting of

the polymer pairs; (4) morphology controlled through flow field and the use of

interfacial modifiers such as block copolymers; (5) combinations of the above

mentioned techniques.

Although miscibility in polymer blends is neither an absolute requirement nor

always desirable, nevertheless, the phase separated alloy often gives inferior

properties if the structure, morphology and interfacial adhesion are not

controlled. On the other hand, an improvement of properties by an order of

magnitude, such as the impact resistance, and the barrier property, can be

achieved through the synergistic effect of a well controlled phase separated

alloying process. Two major factors leading to an understanding of how to

produce desirable heterogeneous blends are: (1) a better knowledge of the

fundamental factors that control blend morphology, interfacial adhesion and

the relationship between the phase demixing kinetics and the equilibrium

thermodynamics of polymer blends; (2) a better understanding of the influence

of the flow field on the mixing and demixing processes.

Small angle neutron scattering (SANS) and time resolved temperature -j ump light

scattering (TJLS) , are basic techniques being used in the group to obtain

information on phase diagrams and demixing kinetics. In addition to these two

techniques, Forced Rayleigh Scattering (FRS), small angle x-ray scattering

(SAXS) and electron and optical microscopy are used in polymer blend studies.

A flow device which allows SANS study in situ has been constructed and used to

study polymer blends under various shear conditions. A similar device for

light scattering which will allow an extension of the study to structures of

larger size is currently under construction.

Fy 88 Significant Accomplishments

® A new procedure for obtaining the temperature, composition, and molecular

weight dependence of the free energy of mixing for polymer blends has

been established. This procedure, which integrates the experimentally

obtained interaction parameter x with theoretical calculations to obtain

a parameterized free energy function of mixing, has been demonstrated by

using a binary polymer blend of polystyrene/poly (vinylmethylether )

.

56
Spinodal and cloud point curves have been generated and found to compare

favorably with experiment.

• The effect of crosslinks between unlike chains in a blend to increase the

compatibility has been studied by SANS technique. Blends of

polystyrene/poly (vinylmethylether) subject to radiation dosage of 125 MRad

have shown an increase of the single phase region of over 250°C.

• A renormalization group treatment of polymers interacting with surfaces

and with excluded volume has been developed. This theory predicts that as

a polymer expands due to excluded volume the probability of surface

contacts becomes diminished so that surface interactions have a reduced

effect on the molecular dimensions. This calculation requires a technical

generalization which is relevant to numerous situations where polymers are

subject to multiple interactions.

® The 10-meter small angle X-ray instrument has been operated as a user

facility successfully. Basic construction of the instrument has been

completed with the installation of a turbomolecular pump for the x-ray

generator and a .beam intensity monitor. Besides in house uses, six

different external academic and industrial organizations have used the

instrument for studies ranging from crystallization kinetics to

microstructures determination in engineering plastics.

Experimental

C. C. Han, R. M. Briber, B. J. Bauer, J. Clark, S. Kruger, J. D. Barnes,

F. J. Mopsik, Y. Matsushita1

, Y. Takahashi1, Q. Tran - Cong2, S. Sakurai3, Y. Qiu4

, H. Kim5, P. Sung6

, P.E. Schoen7

, R. Treanor7

1 Nagoya University, 2 Kyoto Institute of Technology, 3 Kyoto University, 4 East

China Institute of Chemical Technology, 5 University of Wisconsin, 6 FDA. 7 NRL.

Temperature, Composition and Molecular Weight Dependence of Binary Interaction

Parameter of Polystyrene/Poly (vinylmethylether) Blends

The technical importance of polymer blends has been well recognized in recent

years. Making polymers miscible through chemical structure modification is a very important topic, but miscibility may not be the ultimate characteristic

one is looking for. This is because synergistic effects which enhance the

property of a phase separated material mainly come from molecular alignment,

reinforcement, phase domain size and morphology.

In order to understand and possibly control the domain sizes and morphology due

to phase decomposition, one has to understand thermodynamics (statics) as well

as phase separation kinetics (dynamics) . We understand that statics and

dynamics are inseparable subjects if we wish to talk about phase behavior of

even a simple binary system. The most important quantity needed in both static

and dynamic characterization is the free energy (of mixing) of the system as a function of temperature and composition. For the case of polymer systems, we

also need to know the molecular weight dependence of the free energy function.

57
Small angle neutron scattering (SANS) has been used to measure the effective or

scattering binary interaction parameter, xSC att for a deuterated

polystyrene/poly (vinylmethylether) (PSD/PVME) system. This technique offers a

rather simple, fast and accurate method of obtaining the xSC att parameter.

Therefore, a systematic study of this XSC att parameter as a function of

composition, temperature and molecular weight has been carried out.

This measured xSC att can related to the Flory-Higgins Xf

parameter through

thermodynamics relationship if the Xf i s allowed to be composition dependent.

Then, through the compositional dependence of x> » the free energy function of

mixing has been constructed. Spinodal temperatures and cloud point curves have

been generated which compare favorably with experimental values.

Structure and Morphology of MDI/BDO Based Polyurethanes

Polyurethanes are random block copolymers consisting of alternating sequences

of hard and soft segments along the chain. The hard segment is based on

diphenyl methane diisocyanate with butanediol (MDI/BDO) and the soft segment is

based on polytetramethylene oxide. The mechanical properties are believed to

be strongly influenced by the size and shape of the microphase separated hard

segment domains. We have been studying the morphology changes of the hard

segment domains upon deformation by small angle x-ray scattering (SAXS) . As

the sample is stretched in uniaxial tension the hard segment domains which are

initially isotropically arranged begin to orient perpendicular to the

deformation direction. At about 200% stretch the domains begin to break down

and the distinct SAXS intensity maximum observable up to this point begins to

decrease. At very large deformations (>400%, just before failure of the

specimen) a new component to the scattering can be observed at very small

angles oriented normal to the stretch direction. Simultaneously the sample

starts to become opaque. Closer observation with an optical microscope

indicates that the sample is beginning to craze. This behavior of crazing

shortly before failure has been observed for all the polyurethanes studied up

to this point.

SANS of Single Phase Interpenetrating Polymer Networks (IMN's)

We are studying phase separation behavior of single phase IPN's by small angle

neutron scattering (SANS) . The work which was originally centered on blends of

linear poly(vinyl methyl ether) (PVME) and crosslinked deuterated polystyrene

(PSD) has been extended to systems containing mixtures of linear protonated

polystyrene (PSH) and crosslinked deuterated polystyrene. These PSH/PSD

systems tend to phase separate at even lower crosslink densities than the

PVME/PSD system indicating that to make compatible IPN's a negative value of x

(as found in the PVME/PSD system) is a necessity (i.e. requires starting with a

compatible polymer blend before crosslinking) . These results point out the

strong effect of the elasticity of the network that must be included in the

free energy of the system after crossiinking and which destabilizes the system

(causes phase separation) even for normally miscible polymer blends.

58
SANS of Crosslinked Polymer Blends

Work has continued on the phase separation behavior of miscible polymer blends

crosslinked by gamma rays. The effect of introducing crosslinks between the

unlike chains in the blend is to increase the compatible region of the phase

diagram. The blend system studied is poly (vinylmethylether) and deuterated

polystyrene which is examined by SANS to measure the static structure factor as

a function of temperature. Recent work has extended the studies to cover a

wider range of radiation dose (up to 125 MRad) . At the largest dose the effect

on the phase diagram is to increase the single phase region by over 250°C.

Extensions of this work are planned to study the effect of deformation and

swelling in selective solvents on the phase- separation.

Neutron Scattering Studies of Lipid Tubules Formed From a Polymerizable

Surfactant

Small angle neutron scattering (SANS) and wide angle neutron diffraction

studies have been initiated to determine the structure of tubules formed by the

polymerizable lipid, l,2-bis(10, 12- tricosadiynoyl) -sn-glycero- 3 -phosphocholine. A conversion from spherical liposomes to hollow, thin-walled,

cylinders (tubules) occurs as the lipid is slowly cooled through its chain

melting phase transition temperature.

Preliminary SANS and wide angle measurements have been made on suspensions of

tubules and shards in D2 0. A pronounced peak can be observed for tubules in

D2 0 by the SANS experiments which gives the bilayer spacing. No obvious

diffraction signal has been detected from the wide angle measurements conducted

on the same material. This supports the notion that, due to the tight crystal

like packing of the lipid chains, water is completely excluded from the

hydrophilic region. Therefore, there is no scattering contrast between the

lipid chains to give neutron diffraction signals.

SANS measurements have also been initiated on partially deuterated lipid chains

in tubule form. Results will be compared with model calculations of the

scattering function, S(q), determined for various packing arrangements of the

hydrocarbon chains

Effects of Shear on Polymer Blend Critical Phenomena

SANS has been used previously to examine the critical behavior of quiescent

polymer blends. An apparatus for observing the effect of shear in situ at the

NBS SANS facility has been designed and constructed. Preliminary results on

polystyrene/polybutadiene/dioctyl phthalate show an apparent increase in

scattering intensity in the q-region studied by SANS, as shear rate increases

for temperatures below the cloud point (2-phase region) . Above the cloud

point, no change in the scattering intensity is observed. Under no condition

is any evidence of anisotropy observed. Work is continuing on this system as a function of molecular weight, PS/PB ratio, and total polymer concentration.

Work has also been initiated on the design and construction of a light

scattering apparatus for shear systems to provide complementary information.

59
Theory

E. A. Di Marzio, J. F. Douglas, C. M. Guttman

The Free Energy Density of Curved Crystalline Membranes

The He Ifrich form for the free energy of curved membranes is shown not to be

applicable to crystalline membranes. The Helfrich form is shown to derive

from the Frank-Oseen expressions when only the splay part of the curvature

tensor is non-zero. The Frank-Oseen (and also deGennes-Ericsen) free energy

expressions are valid only for liquid membranes. To obtain a more general

expression applicable to crystalline membranes one must obtain invariant forms

by contracting both the director L (and its spatial derivatives) and the

displacement vector u (and its spatial derivative, the strain tensor 6^) with

the 4 indexed symbols C iJkl characterizing the symmetry of the lattice. There

are 7 different kinds of cross terms that can be formed by contracting the

director L, the displacement vector u, and their first derivatives with the

structure constants of the membrane. They are being examined to see which ones

describe curved membranes

.

The Dimensions of Star Molecules

The dimensions of a star molecule are easily estimated by a modification of the

Flory counting scheme. The results for the expanded polymer were shown to be

the same as the Cotton-Daoud results (1.2 power of molecular weight and .40

power of the functionality) . We have now been able to estimate the prefactor

as 1.74. This compares with 1.84 obtained from Monte Carlo modeling.

The Glass Temperature of Rings

The glass temperature of polymeric rings is obtained from first principles for

polyvinypyridine and shown to agree with measurements of Hogen-Esch and

Toreki. The glass temperature of mixtures of rings and linear polymers of the

same species and molecular weight is shown to be a linear function of the

weight fraction of the rings.

i Polymer Localization by Random Impurities

Simple dimensional analysis is employed to discuss the relevance of impurity

interactions on the molecular dimensions of flexible polymers in the limits of

high and low impurity densities. By exploiting an analogy with electron

localization in disordered materials it is found that the presence of random

obstacles generates a net attractive interaction of the polymer for itself

which ultimately leads to chain collapse at a critical density of impurities.

Theoretical predictions agree well with recent Monte Carlo simulations. It is

suggested that the contraction of molecular dimensions, which sometimes occurs

upon heating polymer solutions, can be understood as arising from density

fluctuations ("impurities") in the solvent. The random impurity model is also

qualitatively useful for understanding how a non-homogeneous environment

affects the mean molecular dimensions in numerous more complicated but

practically interesting problems such as gel chromatography, polymers at rough

interfaces, etc.

60
Flexible Polymer with Excluded Volume at an Interacting Surface

A renormalization group treatment of surface interacting polymers with excluded

volume requires a technical generalization which is relevant to numerous

situations where polymers are subject to multiple interactions. The theory

predicts that as a polymer expands due to excluded volume the probability of

surface contacts becomes diminished so that surface interactions have a reduced

effect on the molecular dimensions. A similar effect was previously found in

di-block copolymers where an expansion of the blocks diminishes the effect of

the interblock interaction.

Characterization of Branching Architecture Through "Universal" Ratios

Experimental and Monte Carlo data for dilute solution properties of "lightly

branched" polymers (Stars, combs, rings ...) are compared with the

renormalization group predictions of Douglas and Freed. "Universal"

dimensionless ratios for the mean dimensions of lightly branched polymers,

relative to linear polymers having the same molecular weight, are stressed

since these ratios are useful in characterizing branching architecture. The

reason for the weak dependence of these dimensionless ratios on solvent quality

is described on the basis of the renormalization group theory. Subtle

complications associated with hydrodynamic solution properties and with the

effect of ternary interactions upon theta-point chain dimensions are briefly

discussed. A comparison between theory and experiment is also made for

dimensionless ratios involving the polymer second virial coefficient A2

.

SAXS and Pole Figure Facilities

Digital Camera for Small-Angle X-Ray Scattering

The SAXS facility has been in routine use for over a year. Internal NIST users

have made extensive use of the facility to study topics ranging from matrix

structure of composites to metal uptake by bacteria. Six different external

academic and industrial organizations have used the instrument for studies

ranging from crystallization kinetics to microstructures in engineering

plastics

Basic construction of the instrument was completed with the installation of a turbomolecular pump for the x-ray generator and a beam intensity monitor.

Calibration measurements for establishing an absolute intensity scale are

currently underway.

We are currently constructing a computer-controlled heating stage for high

temperature studies. This will be used to study scattering from blend systems

in the single-phase and phase - separated regimes as well as crystallization

kinetics of semicrystalline polymers, microphase structure in block copolymers,

and similar topics.

61
X~Ray Pole Figure Facility

Extensive measurements have been made on blown films of polyethylene by

scientists from the Mobil Chemical Co. R & D labs. These measurements have

illustrated the need for numerical methods for calculating crystallite

orientation distribution functions from pole figure data.

In conjunction with the University of Virginia we have modified the data

collection software on the pole figure facility to permit collection of data

for crystal structure determinations from fiber specimens.

62
DENTAL AND MEDICAL MATERIALS

The objective of this Group is to provide basic materials science, engineering,

and test methods which may be used by sectors of the health-care industry for

the development of new or improved materials, delivery systems, and standards.

Although no current effort is in progress on diagnostic systems, plans do

include these activities for the future.

Materials -research efforts, aimed at development of materials and techniques

for promoting adhesion to tooth, dentin, enamel, bone, and soft tissues, are

pursued for reducing marginal leakage of restorations via utilization of

adhesives and durable space occupying materials for use in cavity preparations.

These include new composite resin formulations with reduced polymerization

shrinkage and more resistance to attack by oral fluids as well as macroscopic

bulky space fillers bonded to cavity walls. Strong, more durable, versatile

dental cements are also explored. The durability of dental materials is

investigated by pin-on-disc wear studies and by characterization of aged

materials by the application of the Weibull method of statistical analysis.

Studies of calcium phosphate compounds for endodontic sealants, bone

augmentation, or caries -reducing agents are being investigated. The basic

chemistry of precipitation of calcium phosphates is explored as it relates to

formation of mineral deposits such as bone, teeth, and atherosclerotic plaque.

Theoretical and experimental studies of stresses within bonded dental systems

are explored with the objectives of defining the most compatible material

property and geometrical design combinations for porcelain- to-metal , tooth- toresin, resin- to-filler bonding and so forth. Characterization of materials by

Weibull statistics is being employed with a view toward using those parameters

with finite element stress analysis for evaluation of the reliability of dental

systems

Techniques for characterizing the effects of compositions on the casting

behavior of alloys are being published with a view toward improved alloys and

processing methods.

FY 88 Significant Accomplishments

• Initiated three monthly series of communications with dental industrytrade -profess ion .

® In the study of spiro orthocarbonate monomers capable of double ringopening polymerization with an expansion in volume, a novel monomer was

prepared which exhibits reactivity comparable to conventional methacrylate

monomers and high ring-opening efficiency at near ambient polymerization

conditions

• A novel dental restorative, a hybrid cement-composite, has been developed

in order to overcome the propensity of conventional glass - ionomer cements

to brittle fracture during wear from occlusion. The restorative involves

the usual hardening of a commercial glass - ionomer cement along with the

polymerization of a water-soluble monomer (e.g. hydroxyethyl methacrylate)

incorporated in the system to provide toughening. bn vitro tests revealed

63
good wear resistance, excellent oral -environmental resistance, and no

catastrophic failure during wear.

• Newly synthesized low molecular weight polymers prepared from vinyl and

isocyanate containing monomers adhere at least as well to glutaraldehyde

treated dentin than the most efficient dentin bonding agents, thereby

providing another potential alternative bonding system for dental

applications

.

• An "ultrasimplified" two-step system for bonding dental resins to hard

tooth tissues has been developed, streamlining a multistep procedure

developed by ADA Health Foundation research associates in 1981.

Wear. Durability. Clinical Studies and Related Properties of Dental Composites.

Amalgams. Cements and Glass-Ionomer Cements

J. M. Antonucci, W. de Rijk, J. E. McKinney, J. A. Tesk, R. L. Bowen1

, F. C. Eichmiller1

, A. A. Giuseppetti 1

, K. Kula2, A. Ly, D. Palmer4, N. E. Rupp 1

, S. Venz3

, and R. W. Waterstrat1

1 ADAHF/PRO

2 Dental School, University of Maryland, Baltimore, MD and NBS

3 Dentaply International, York, PA

4 U.S. Navy, Dental School, Bethesda, MD

A study was initiated to measure the effect of the submersion of dental

composites in 70% ETOH for a prolonged period of time (up to 6 months) . In

order to adequately characterize the material using a Weibull distribution, 60

samples were made for each of 4 time intervals. In a related effort the effect

of filler content on the Weibull modulus of an experimental composite resin is

being studied. A resin/powder ratio of 0.20, 0.25, 0.50 as well as unfilled

resin has been used to make 60 samples of each composite to determine the

Weibull modulus and the characteristic strength.

Studies were continued on the development of an experimental dental composite

restorative containing a fluorinated flexible resin in an attempt to improve

wear and oral -environmental resistances. A dual cure (chemical and visiblelight activated) was employed to increase the degree of cure, which is

viscosity limited. Wear tests on these composite specimens preconditioned in

food- simulating liquids revealed good environmental resistance; however, the

wear rate was still larger than desired.

In collaboration with the University of Maryland Dental School, studies are

being continued on the influence of various topical fluoride-gel treatments on

selected commercial dental composites. These studies involve in vitro wear

tests (NIST), weight losses from gel treatments, microdefect analysis, and

clinical tests. In cases where significant weight losses were observed, the in

vitro wear resistance often improved. SEM studies on these specimens revealed

polymer-rich layers on the wear tracks, which apparently resulted from

portions of inorganic filler being etched out by the gel treatments. During

64
wear the voids were filled with residual resin, which apparently provided a

lubricating effect.

In collaboration with the Naval Dental School the wear of human enamel against

a commercial castable-ceramic restorative materials was measured. This

quantity was compared to that for enamel wearing against a conventional

porcelain, used as a control. There was no significant difference between the

enamel wear from the castable ceramic and porcelain, which means that the

former is satisfactory in this respect. However, if the ceramic was shaded

using a glaze provided by the manufacturer, the wear rate of the enamel

increased by a factor of two. Accordingly, this glaze should not be applied to

stress -bearing occlusal surfaces.

Preliminary measurements have been made to determine the amount of wear on

synamel (sintered polycrystalline hydroxyapatite) , used to simulate human

enamel, against titanium. The wear from titanium is being compared with that

using other commercial alloys which bracket titanium with respect to hardness.

Paradoxically, the softest alloy, containing gold, produced the most wear on

the synamel. The hard alloys, including titanium, tended to polish the

synamel, apparently reducing friction, which, in turn, reduced the wear rate.

More work is necessary, including improved microdefect analyses, to assess the

various wear mechanisms and to determine the relevance to corresponding in

vitro wear involving occlusion with enamel.

The development of a new, automated, pin on disc, dental-wear apparatus has

continued. This apparatus will be able to make continuous wear measurements on

specimens under selected media to simulate the intraoral environment.

A final progress report has been written and submitted for NBS review

concerning high- temperature neutron-diffraction studies on the Ti-Al alloy

system. Our studies have revealed the existence of short-range atomic ordering

which is critically affected by small amounts of dissolved oxygen. We have

also discovered a hitherto unknown high- temperature phase at about 40 atompercent Al which appears to have a hexagonal close-packed structure.

Ongoing research into resin-modified glass - ionomer cements resulted in the

development of two new types of these hybrid cement composites. One type is

based on the use of an aqueous polymer solution (rather than just water or

water plus tartaric acid) with the powder component of a water hardening glass

ionomer cement. Water soluble polymers such as gelatin, polyethylene oxide,

polyethylene glycols, etc. were investigated. The resulting hybrid cement

composites exhibited less propensity to brittle failure and excellent tensile

strength. A second type also employed a water soluble polymer but in

combination with a water-compatible, polymerizable resin. This type of

formulation also yielded toughened hybrid cement-composites.

In the second phase of a NIDR contract to clinically evaluate the ferric

oxalate -NPG- PMDM dentin-enamel adhesive system, more than 150 permanent

restorations have been placed to permit clinical performance of these materials

over three years. Most restorations required only hand instrumentation without

anesthetic or cavity retention form. Application of this adhesive system to

65
cementation of castable ceramics and desensitization of dentin are currently

being explored clinically.

Techniques for shielding soft tissues adjacent to metallic dental restorations

during head and neck radiation therapy have been demonstrated clinically during

the past year. Current research is focusing on characterizing the dose-depth

scatter enhancement of different restorative materials subject to different

treatment energies. A simulating phantom has been designed to study

restorative materials exposed to Cobalt 1.2 and Linac 4,6,10 and 20 MeV

radiation sources.

Observations of single- tooth precision-cast titanium restorations in place

after 34 months indicate some wear on opposing teeth. Epoxy models of these

castings and teeth, are being evaluated by direct profilometry to determine the

location and extent of this wear. The clinical compatibility of these castings

with oral tissues appears excellent at this time.

Clinical trials of class I, III and VI composite restorations using glass

inserts have been successful in developing techniques and instrumentation for

application and handling of the inserts. Newly formulated microcrystalline

glasses are currently being investigated.

Medical Materials: Improved Tissue Adhesive and Improved Surgical Bone Cement

G. M. Brauer, J. W. Stansbury, C. Lee 1

1 Sichuan Medical College, Chengdu, Peoples Republic of China

To study the biocompatibility of tissue adhesives with pendant isocyanate

groups, samples of oligomers and cemented bone specimens were sent to various

laboratories (Northwestern University, University of Texas, El Paso, University

of South Carolina, Indiana University, University of Regensbung, Germany,

University of Manchester, England, University of Calgary, Alberta, Canada). A

cyanoacrylate formulation was prepared for the Medical School, Vanderbilt

University

.

Over 20 new oligomers containing pendant isoyanate groups were synthesized from

various vinyl monomers, m- isopropenyldimethylbenzyl isocyanate (TMI) and 2-

isocyanatoethyl methacrylate. Dilute oligomer solutions adhere as well or

better to glutorraldehyde treated dentin than other bonding agents and the soft

tissue and dentin base resin. However, the formulations containing the

previously synthesized methacrylate esters are the most efficient adhesives for

bone. Bond strength does not depend on the isocyanate content of the oligomer

and is independent of molecular weight.

66
ralMnm Phosphate Chemistry. Biochemistry. Structure and Clinical Implications

J. M. Antonucci, W. E. Brown1

, C. M. Carey1

, L. C. Chow1, N. Eidelman1, E.D.

Eanes2, B. 0. Fowler2

, Y. Fukase, T. M. Gregory1

, A. W. Hailer2, M. Mathew1, D.

N. Misra1

, B. A. Sieck1

, S. Takagi 1

, B. Tomazic 1

, M. S. Tung1, and G. L. Vogel 1

1 ADAHF/PRC

2 National Institute of Dental Research (NDIR) at NIST

Chemical and crystallographic investigations of octacalcium phosphate (OCP) , a

precursor in the formation of tooth mineral, and its role in biomineralization

have continued. The OCP -dicarboxylate system was studied, including simple

dicarboxylic acids and several derivatives such as amino acids and unsaturated

acids. Preliminary results indicate the incorporation of fumarate ions into

OCP. Attempts to prepare single crystals of these complexes suitable for

structural studies are continuing.

The maturation of amorphous calcium phosphate (ACP) , that is, the

transformation of ACP to crystalline apatite, was studied by monitoring the

change in crystallinity, using x-ray powder diffraction. A study of the

process indicates the formation of an intermediary phase, which appears to be

OCP. Results of the study indicate that ACP has potential application for

remineralization and/or fluoridation.

Investigations of demineralization and remineralization of dental specimens

using synchrotron radiation and x-ray magnification raicroradiographic

techniques have continued. High-resolution microradiographs have been obtained

of dental specimens of various thicknesses using a range of x-ray energies.

Apatitic fluoride content of tooth mineral was increased by treatment with a calcium phosphate solution containing complex fluoride compounds such as sodium

f luorostannate and sodium f luorosilicate . A single treatment incorporated

approximately 3000 ppm fluoride as apatitic fluoride. This process was also

evaluated for effectiveness in remineralizing artificially formed lesions in

enamel of extracted teeth. The procedure appears clinically feasible because

of the relatively short treatment time.

Fluoride uptake from low level fluoride sources has been measured using a constant composition method without enamel biopsies. Results indicated

absorption in fissures of extracted human molars from solutions containing as

little as 0.05 ppm fluoride when activated by a dicalcium phosphate dihydrate

forming treatment.

Two constant composition methods were used for investigation of the labile and

permanently bound fluoride uptake produced by topical treatments and the

concomitant increase in tooth resistance to lesion formation. Fluoride uptake

was highest and lesion formation lowest in a four-minute experimental treatment

with dicalcium phosphate- forming solution followed by acidulated phosphate

fluoride

67
In vitro tests of the calcium phosphate cement developed by research associates

in the ADA Health Foundation's Paffenbarger Research Center showed that it

fills and seals root canals as well as or better than the gutta-percha/Grossman

cement system now in wide use. Animal studies have shown that the cement

causes no long-term detrimental effect on periapical tissues.

A study was made to determine whether a slurry containing equimolar amounts of

tetracalcium phosphate and dicalcium phosphate dihydrate in water can effect

remineralization of artificially formed lesions in the roots of extracted

teeth. The procedure resulted in a substantial increase in mineral density in

the outer 30 micrometers of the lesion and a smaller increase in the rest of

the lesion. The treatment appears practical because the chemical nature and

consistency of the slurry renders it safe and easy for overnight applications

without using chemical retaining trays.

Microanalytical techniques were used to study the solubility of tooth enamel by

measuring the compositions of dilute acid solutions placed in micrographic

wells drilled into the sound and carious regions of tooth specimens. Carious

enamel was significantly less soluble, probably because of loss of carbonate

and other soluble constituents during caries formation. Residual apatite

crystals might have higher fluoride concentrations which would make them less

soluble in acidic solutions,.

Cardiovascular deposits may be represented as apatitic phases with substantial

sodium, magnesium, and carbonate substitutions. They are formed by hydrolysis

of octacalcium phosphate to a complex hydrolyzate. A systemic investigation of

carbonate substituted hydrolyzates was undertaken. The findings provide new

evidence that OCP is a precursor in formation of pathologic calcified deposits.

Further analyses of precipitated nearly- stoichiometric hydroxyapatites (HAs)

indicate about one water molecule per unit cell is structurally incorporated in

these HAs. Insufficient vacant lattice sites were found by chemical analyses

to accommodate this water. Hence, the unit-cell symmetry may be distorted from

hexagonal to spatially fit this water, and experiments are under way to test

this hypothesis.

Acidic phospholipids (APL) help regulate mineral formation in matrix vesicles,

the sites of initial calcification in many skeletal tissues. Results from

model liposome studies suggest that this regulation is affected by the location

of the APLs in the MV's covering bilayer membrane. Inside monolayer APLs delay

the appearance of extravesicular mineral; external APLs delay subsequent

growth. Results also showed that other membrane constituents can affect

mineral development indirectly by altering the transmembrane APL distribution.

Several new types of fillers for dental composites based on calcium

metaphosphate chemistry were developed. Calcium metaphosphate (CMP) is a

unique phosphate mineral existing in four crystalline forms and one amorphous

form and possessing a polymeric structure. The forms have refractive indices

that are optically compatible with BIS-GMA type resins, thereby permitting

their use in visible light activated composite formulations. In this study,

crystalline /3-CMP and vitreous CMP were prepared, ground to particle sizes

between 1 and 25 urn, characterized and then evaluated as fillers for composites

68
using photoactivated resin systems. Depth of cure was of the order of 5-6 mm

using 40 seconds of irradiation from a commercial blue light source.

Dental Polymer. Composite. Cement. Sealant, and Adhesion Chemistry

J. M. Antonucci, G. M. Brauer, J. W. Stansbury, R. L. Blosser1

, R. L. Bowen1, F. C. Eichmiller1

, M. Farahani, A. D. Johnston1

, N. W. Rupp 1

, A. Sugawara3 and

S . Venz4

1 American Dental Association Health Foundation, Paffenbarger Research Center.

(ADAHF/PRC) at NIST

2 Dental School, Georgetown University, Washington, DC

3 Nihon University, Tokyo, Japan

4 Dentsply International, Milford, DE

Composites formulated with fillers of vitreous CMP expanded on storage in water

but had relatively low strength, whereas those based on ,5-CMP were much more

moisture resistant, stronger and showed a tendency to arrest brittle fracture.

These novel fillers have potential application in a number of other resin based

materials and dental cements

A study was initiated to ascertain if the formation of hydroxyapatite occurs

from tetracalcium phosphate (TTCP) and dicalcium phosphate (DCP) when the

latter are contained in hydrogels formed by self -curing reactions.

Hydroxyapatite formation occurred in hydrogels derived from poly (alkenoic

acids) such as poly(acrylie acid) but not in hydrogels derived from 2-

hydroxyethyl methacrylate with crosslinking monomers. The calcium polyacrylate

cement that resulted from TTCP or TTCP/DCP shows promise as a dental cement.

To enhance the conversion of vinyl groups in dental resins several approaches

are being pursued. One approach involves using highly reactive vinyl monomers

such as a-methylene /3-butyrolactone . Several substituted vinyl lactones have

been synthesized that are expected to have, in addition to their high

reactivity, improved solvent resistance and low polymerization shrinkage.

Still another method for improving the extent of polymerization involves

developing more efficient initiator systems (e.g. dual cure initiators

combining photochemical and chemical activation) . Using several types of dualcure initiators, significant improvements in the conversions, hardness, tensile

strengths and solvent resistances of dental resins and their composites were

obtained.

The study of monomers capable of free radical, double ring-opening

polymerization with an expansion in volume has been focused on a particular

spiro orthocarbonate system which optimizes both reactivity and ring-opening

efficiency (and thereby expansion) . An aromatic - substituted monomer has been

synthesized which exhibits complete ring opening under all polymerization

conditions investigated. This monomer also yields polymers with increased

glass transition temperatures relative to previous ring-opened polymers.

69
In contrast to these spiro, ring-opening monomers, a new class of difunctional

monomer which can polymerize by an intramolecular ring closure pathway are

being synthesized and evaluated. By this process, polymers have been prepared

in which quantitative conversion of the double bonds has been achieved. A

project to determine whether this monomer can reduce the residual unsaturation

in conventional composites is currently underway.

An alternate approach to improving both the conversion and chemical resistance

of resin-based dental materials involves the use of highly reactive vinyl

lactone monomers. A series of substituted methylene butyrolactones were

prepared and polymerized to demonstrate that variation of the side chain

functionality could drastically alter the solvent resistance of these noncrosslinked polymers. Polymerization shrinkage and glass transition

temperature were also related to the substituents.

Work has continued on improving the adhesive bonding system developed by

research associates in the ADA Health Foundation's Paffenbarger Research

Center, (PRC), and on determining conditions for packaging, dispensing and

storing the components. A two-step system that can be completed in less than

two minutes, greatly simplifies the treatment for both enamel and dentin and

gives tensile bonds equivalent to the previous three- solution protocol.

Methods have been developed for testing adhesion and microleakage at

temperatures closely simulating oral conditions. These new techniques allow

determination of the effects of body temperatures on bond strengths and sealing

abilities of esthetic restorative systems.

New monomers have been synthesized for protective tooth coatings. The first

was the reaction product of pyromellitic dianhydride and 2- (N- tertbutyl)

aminoethylmethacrylate

.

Electron paramagnetic resonance (EPR) spectroscopic analysis revealed the

presence of free radicals in ground enamel and dentin. This phenomenon will be

studied to determine if free radicals in the instrumented tooth surfaces help

initiate the "spontaneous" polymerization of the PRC developed adhesion system

monomer

.

Dental Alloys, Ceramics. Metrology, and Analysis

J. M. Antonucci, M. Chiang, W„ de Rijk, J. E. McKinney, R. W. Penn, K. Asaoka1

, R. L. Bowen2

, F. C. Eichmiller2, A. A. Giuseppetti2, R. W. Hinman4, 0. Okuno5

, Y. Sato6 and R. W. Waterstrat2

1 Tokushima University School of Dentistry, Tokushima, Japan

2 ADAHF/PRC

3Naval Dental Clinic, San Diego, CA

4 Tokyo Medical and Dental University, Tokyo, Japan

Hiroshima Dental School, Hiroshima, Japan

A finite element analysis was conducted to explore the effects of material

properties, cooling rates and thickness ratios for a three layered porcelainopaque-metal slab. Results show high transient tensile stresses at the metal70
opaque interface during cooling and high residual surface stresses cooling.

The magnitudes may be altered by changing the thermo -physical properties of the

materials involved.

Recent work has focused on designing more effective methods for casting

titanium and the development of commercially feasible casting machines. These

advances, coupled with the development of new casting investments and porcelain

bonding techniques have made the production of titanium dental castings a

viable commercial enterprise.

The development and study of alloy phase diagrams has shown that alloys of

certain metals are especially promising for use in dentistry. The include

hafnium, molybdenum, niobium, tantalum, and other less common metals which are

relatively inexpensive. Work is continuing in analyzing alloy systems which

exhibit ductile behavior, especially those having stress - induced

transformations

The use of the Weibull distribution has shown that for the diametral tensile

strength data of one composite resin, more than one failure mechanism seems to

exist. A mixed Weibull was found for the failure data with two distinct

Weibull parameters. The characteristic strength remained unchanged.

The Weibull method of analysis was also applied to porcelain- to-metal system

fracture data. The effect of two methods of reglazing on the overall system

strength was measured. No major difference were observed but it was learned

that a larger number of specimens is needed to discern secondary effects.

Preliminary results on resin bonded bridges placed at the University of

Maryland Dental School have been used to determine a characteristic service

life for that particular restoration by treating the data as a censored Weibull

distribution of times to failure.

High temperature strain gauges have been embedded in phosphate bonded

investments in order to determine the thermal expansion at the site of the wax

pattern. The strain gauges recorded the onset of the phase transitions of the

filler particles very reproducibly . Reversible phase transitions were observed

on heating and cooling. The amplitude of the strain observed is several orders

of magnitude larger than the strain gauges could tolerate, indicating that

unexplained electrical signals are generated during the heating cycle which

obscure the actual strain information.

Dental instruments and handpieces can be degraded by autoclaving and cold

sterilization is not very effective against viral and spore mediated diseases.

An investigation has begun using a microwave magnetron as the RF source for

producing a gas plasma. Preliminary results have shown that bacterial spores

can be inactivated by an exposure to the plasma of 10 minutes duration.

Microwave radiation alone did not produce inactivation. The gas plasma caused

severe heating of the vacuum chamber walls , which requires further

investigation.

71
A modified composite bending beam is being designed for the evaluation of the

resin-etched-metal system strength. A casting technique has been developed to

produce the specimen with the particular dimensions.

A new electric arc furnace has been designed and constructed which will permit

casting large dental appliances, such as partial dentures, from titanium-based

alloys. Further testing will probably stimulate commercial activity in this

field. Such devices will also be useful in the rapidly- growing field of dental

implants where titanium castings can play a critical role.

72
OUTPUTS/INTERACTIONS

Publications

Antonucci, J. M. Toughened glass-ionomer cements. Trends and Techniques

4:1988.

Antonucci, J.M.; Stansbury, J.W.; Venz, S. Synthesis and properties of a

polyfiuorinated prepolymer multifunctional urethane methacrylate. Polym.

Mat. Sci. Eng., Proceedings of the ACS Division of Polymeric Materials,

Vol.59, 1988.

Kuo, J. $. ; Antonucci . J. M; Wu, W. L. ; Venz, S. Evaluation of siloxanecontaining dental composites. J. Dent. Res. in press,

Singh, Surenda; Katz, J. Lawrence; Antonnuci. J

: Penn, R. W. ; Tesk, J.A.

The elastic properties of glass reinforced dental composites. Journal of

Non-Crystalline Solids 102 (1988) p. 112-116.

Singh, S.; Katz, J.L.; Antonucci. J.M. : Penn, R. W. ; and Tesk, J.A.

Ultrasonic measurements of the elastic properties of dental materials.

Proceedings of Third World Biomaterials Congress, April 21-25, 1988,

Kyoto, Japan, p.118.

Barnes, J. D. ; Mopsik, F. I. Small angle x-ray characterization of

polymers. SPE 1987 ANTEC Meeting, April 1988.

Bauer, B. J.; Briber, R. M. Han, C. C. SANS studies of compatible blends

of PVME and crosslinked deuterated polystyrene. Macromolecules, in press.

Bauer, B. J., Briber, R. M. , and Han, C. C., Synthesis and

characterization of poly (vinylmethylether) , accepted for publication in

Polymer Communications.

Factor, B. J.; Smith, B. A.; Russell, T. P.; Bauer . B. J.; Han, C. C.

Phase separation of star- linear polymer mixtures. Polymer Preprints, ACS,

1988 , in press

Blair, W. R. ; Parks, E. J.; Olson, G. J.; Brinckxnan, F. E.

Characterization of organotin species using microbore and capillary

liquid chromatographic techniques with an epifluorescence microscope as a novel imaging detector. J. Chrom. 410 : 383 ; 1987

Blosser, R. L. ; Bowen . R. L. Effects of purified ferric oxalate/nitric

acid solutions as a pretreatment for the ntg-gma pmdm bonding system.

Dent. Matls . , in press.

Bowen, R. L. Dentin adhesive bonding. Update, August/September 1987.

Bowen, R. L. ; Tung, M. S.; Blosser, R. L. ; Asmussen, E. Dentine and

enamel bonding agents. Inti. Dent. J. 37: 158; 1987.

73
Chohayeb, A. A.; Bowen . R. L. ; Adrian, J. Pulpal response to a dentin and

enamel bonding system. Dent. Matl. M: 144; 1988

.

Asmussen, E. ; Bowen . R. L. Adhesion to dentin mediated by gluma: effect

of acidic pre treatment with various amino acids. J. Dent. Res.

95 : 521 ; 1987

.

Bowen, R. L. Review of the paper: bonding agents and adhesives, by R. W.

Phillips, Proc. of the Inti. State of the Art Conf. on Restorative

Materials, in press.

Brauer, G. M. Vanillate and syringate cements. Trends and Techniques 6:

1988.

Brauer, G. M. Color changes of composites on exposure to various energy

sources. Dent. Mater. 4: 55; 1988.

Xizuka, H. ; Brauer . G. M. ; Rupp, N. W. ; Ohashi, M. ; Paffenbarger , G.

Forces fracturing cements at die interfaces and their dependences on film

thickness. Dent. Matl. 3: 187; 1987.

Briber, R. M. ; Bauer, B. J. The effect ©f crosslinking on the phase

separation of a miscible polymer blend. Macromolecules, in press.

Briber, R. M. ; Khoury, F. A. Electron energy loss spectroscopy:

application to synthetic organic polymers. J. Poly. Set. Poly. Phys . Ed.

26 : 621 ; 1988

.

Brinckman, F. E. ; Olson, G. J.; Blair, W. R, ; Parks, E. J. Implications

of molecular speciation and topology of environmental metals: uptake and

toxicity of organotins. ASTM STP 971 : 219 ; 1988

.

Brinckman, F. E. ; Olson, G. J. Microbiological materials processing.

J. of Metals, in press.

Matthias, C. L. ; Be llama , J. M. ; Brinckman . F. E. Determination of

tributyltin in estuarine water using bonded c-18 silica solid phase

extraction, hydride derivatization and GC-FPD, in Proc. Oceans 87 Conf.

4 : 1344 ; 1987

.

Eng, G. ; Brinckman . F. E. ; Johannesen, R. B,; Tierney, E. J.; Bellama, J.

M. Holistic conformational and total surface area calculations as

predictors for solution properties and chromatographic parameters:

organometals . J. Chromatogr. 403:1; 1987.

Brinckman, F. E. ; Olson, G. J. Global biomethylation of the elementsits role in the biosphere translated to new organometallic chemistry and

biotechnology. The Bioalkylation of Heavy Elements, Spec..Publ. 66, Royal

Soc. Chem. , London (1987), in press.

74
Brinckman, F. E. Transnational oceanic measurement intercalibration and

databases as cooperative tools in the pacific basin: The biogeochemical

prospect, Proc. Conf. on the Yellow Sea, M. Valencia, ed. , Honolulu, HI,

in press.

Tierney, E. J.; Bellama, J. M. , Eng. G. ; Brinckman. F. E. and R. B.

Johannesen. Total Molecular Surface Areas as a Predictor for ReversedPhase High Performance Liquid Chromatography in Various Organotin

Systems, "Importance and Application of Carbon Hygridization Summaries".

J , Chromatogr. . 441 . 229-237 (1988).

Eng, G. ; Tierney, E. J.; Bellama, J. M. , Brinckman. F. E. Correlation

of molecuir total surface area with organotin toxicity for biological and

physicochemical applications. J. Appl. Organometal. Chem. , 2, 171-175

(1988).

Degnan, T. F. ; Weiss, C. S.; Brinckman . F. E. ; Rankel, L. A. The

speciation and removal of arsenic present in whole and processes shale

oils. Fuel, in press.

Eng, G.; Tierney, E, J.; Bellama, J. M. ; Brinckman . F. E. Correlation of

molecular total surface area with organotin toxicity for biological and

physicochemical applications. J. Appl. Organometal. Chem. 2: 171; 1988.

Broadhurst, M. G. ; Chiang, C. K. ; Wahlstrand, K. J.; Hill, J. M. ; Dissado, L. A.; Pugh, J. The dielectric properties of biological tissue

(crassula portulacea) from 10" 2 to 109 hz, J. Mol. Liq. 36: 65; 1987.

Broadhurst, M. G. ; DeReggi, A. S.; Davis, G. T. ; Mopsik, F. I. Charging

behavior of polyethylene and isonomers. IEEE Conf. on Electric Insulation

and Dielectric Phenomena, 1987.

Brown, W. E. ; Chow, L. C. A new calcium phosphate, water- setting cement.

In: Cements Research Progress 1986 . P. W. Brown, Ed., Westerville, OH:

American Ceramic Society, pp . 352-379, 1987.

Brown, W. E. ; Eidelman, N. ; Tomazic, B. B. Octacalcium phosphate as a precursor in biomineral formation. Adv. Dent. Res. 1 (2) : 306 ; 1987

Bur, A. J.; Roth, S. C. Preparation of Thin Film Polyvinyl idene Fluoride

Shock Wave Pressure Transducers. NBSIR 87-3680, December 1987.

Bur, A. J.; Wang, F. W. ; Dehl, R. E. In situ fluorescence monitoring of

the viscosities of particle- filled polymers in flow. NBSIR 88-3694,

January 1988.

Bur, A. J.; Wang, F. W. ; Lowry, R. E. Fluorescence monitoring of polymer

processing. Proc. JANNAF Conf. on Propellant Char., Johns Hopkins APL,

October 1987.

75
Bur, A.J.; Wang, F. W. ; Lowry, R.E. Fluorescence monitoring of polymer

processing: mixing and zero shear viscosity. Proc. SPE Annual Mtg. , April

1988.

Carey, C. M. ; Chow, L.C.; Tatevossian, A.; Vogel, G. L. Extracellular

potassium concentrations in human dental plaque fluid recovered from

singles sites. Arch. Oral. Biol., in press.

Carey, C. M. ; Gregory, T. M. ; Tatevossian, A.; Vogel, G. L. The buffer

capacity of single site resting plaque fluid. Arch. Oral. Biol., 33:7;

487, 1988.

Carey, C. M. ; Vogel, G. L. ; Chow, L. C. Determination of extracellular

fluid volume in whole dental plaque using potassium- or chloride

selective microelectrodes. J. Dent. Res., J. of Dent Res 67(5) : 866-869

,

May 1988.

Chai, H. , Mode II and Mode III interlaminar fracture of laninated

composites, in proceedings of 4th Annual ASM/ESD Conference on Advanced

Composites

Chang, S. S.; Mopsik, F. I.; Hunston, D. L. Correlation of cure

monitoring techniques. Proc. 19th Inti. SAMPE Tech. Conf. 19: 253; 1987.

Chang, S. S. Multiple glass transition in bimodal polystyrene mixtures.

Poly. Comm. 29:33;1988.

Chang, S. S.; Guttman, G. M. ; Sanchez, I. C. ; and Smith, L. E.

Theoretical and computational aspects of migration of package components

to food, Chapter 9, Food & Package Interaction, J. H. Hotchkiss, Ed., ACS

Syrup . Ser. 365 : 106 ; 1988

.

Chang, S. S. Multiple melting peaks of poly(aryl ether ether ketone),

Poly. Comm. 29:138; May 1988.

Chang, S. S. Heat of reaction and curing of epoxy resins. J. Thermal

Anal., 34: 135; 1988.

Chang, S. S. Thermal Analysis of VAMAS Polycarbonate/Polyethylene blends,

Thermochim. Acts (1989).

Chang, S. S., Hunston, D. L. and Mopsik, F. I., Cure monitoring

techniques for thermoset resins. Proc. 4th Advanced Composites Conference

and Exhibition, (1988).

Chiang, C. K. ; Cook, L. P. ; Chang, S. S.; Blendell, J.; Roth, R. S. Low

temperature thermal processing of superconducting ceramics, Bull. Sp

.

Pub. Adv. Ceramics, in press.

Chow, L. C.; Brown, W. E. Diffusion controlled dissolution and

precipitation. Croatica Chemica Acta 60: 591; 1987.

76
Kuriyama, M. ; Dobbyn, R. C.; Takagi, S.; Chow, L. C. Microradiography

with an x-ray image magnifier. Biophysics (Japan) 27: 54; 1987.

Chow, L. C. Calcium phosphate materials: reactor response. Adv. Dent.

Res . , in press

Clark, J. C.; Miller, W. G. ; Wellinghoff, S. T. Rheological properties of

atactic polystyrene/carbon disulfide gels. Poly. Comm., in press.

Crissman, J. M. ; Guttman, C. M. ; Maurey, J. R. ; Fanconi, B. M. ; VanderHart, D. L. ; Wang, F. W. ; Reference standard polyethylene resins

and piping materials. NBSIR 88-3705, January 1988.

Crissman, J.M.; Zapas, L. J.; Approximate relations for the analysis of

single step stress -relaxation data in uniaxial extension from experiments

involving a finite step time. Polymer, in press.

Davis, G. T. Piezoelectric polymer transducers. Adv. Dent. Res.

1(1) :45 ; 1987

Davis, G. T. Structure, morphology and models of polymer ferroelectrics

The Applications of Ferroelectric Polymers, Chapter 4, pp . 37, Blackie

and Son Ltd., 1987.

DeReggi, A. S.; Broadhurst, M. G. ; Davis, G. T. ; Mopsik, F. I.

Measurement of space charge fields in polymers. IEEE Conf. on Electric

Insulation and Dielectric Phenomena, 1987.

Doverspike, M. ; Conradi, M. S.; DeReggi . A. S.; Cais , R.E. Deuterium NMR

study of orientation and poling in polyvinyl idene fluoride.

Macromolecules, in press.

Lewin, P. A.; DeReggi . A. S. Short range transducer applications of

ferroelectric polymers. The Applications of Ferroelectric Polymers,

Chapter 7, pp . 162, Blackie and Son Ltd., 1987.

de Rijk, W. G.; Tesk, J. A.; Penn, R. W. The nonnormal distribution of

failure stresses in a porcelain to metal systems evaluation. Proc . 6th

Southern Biomedical Engineering Conf., Oct. 1987.

de Rijk, W. G. ; Penn, R-.W. ; Tesk, J.A. and Zapas, L.J. Dental

composites: strength properties via Wubull statistics. Proceedings of

Third World Biomaterials Congress, April 21-23, 1988, Kyoto, Japan,

p.251.

de Rijk, W. G.; Tesk, J. A.; Penn, R. W. and Marsh, J. Applications of

the Weibull method to statistical analysis of strength parameters of

dental materials. Polym. Mat. Sci. Eng., Proceedings of the ACS Division

of Polymeric Materials, Vol.59, 1988.

Dickens, B. ; McCrackin, F. L. System of Hardware and Software Developed

for Size Exclusion Chromtography . NBSIR 87-3669, November 1987.

77
Dickens, B. ; McCrackin, F. L. System of pc computer programs for size

exclusion chromatography,, ACS, Div. Poly. Sci„ Eng., 58 :465-468 : 1988

.

Dickens, B.; McCrackin, F. L. Automatic measurement and processing of

size exclusion chromatograms using microcomputers. ACS Symp. Series, in

press

.

Di Marzio, E. A.; Passaglia, E. Calculations of the amount of adjacent

re-entry in polymer crystallization, I. the basic equations, J. Chem.

Phys. 87(8) :4901 ; 1987.

Di Marzio, E. A. Dimensions of diblock copolymers. Macromolecules, 21 . 2262-2269' (1988).

Douglas, J. F. Polymer localization by random fixed impurities: Gaussian

chains. Macromolecules (in press).

Heywood, B. R. ; Eanes . E. D. An ultrastructural study of calcium

phosphate formation in multilamellar liposome suspensions. Calcif. Tiss.

Int. 41: 192; 1987.

Arends , J.; Christoffersen, J.; Christoffersen, M. R. ; Eckert, H. ; Fowler . B. 0.; Heughebaert, J. C„; Naneollas, G. H. ;Yesinowski , J. P.;

Zawacki, S. J. A calcium hydroxapatite precipitated from an aqueous

solution - an international multimethod analysis. J. Crys. Growth, in

press

.

Guttman, C. M. Flow of Molecules Through Condoms. NBSIR 88-3721, February

1988.

Han, C. C.; Bauer, B. J.; Clark, J. C.; Muroga, Y. ; Matsushita, Y. ; Okada, M. ; Tran- Cong, Q, ; Chang, T. Temperature composition and molecular

weight dependence of binary interaction parameter of polystyrene/poly

( viny lme thy 1 ether) blends. Polymer, in press.

Hasegawa, H.; Tanaka, T.; Hashimoto, T.; Han . C. C. SANS and SAXS studies

on molecular conformation of a block polymer in microphase space. II.

Contrast matching technique. Macromolecules 20 : 2120 ; 1987

.

Sato, T. ; Han . C. C. Dynamics of concentration fluctuation in a polymer

blend on both sides of the phase boundary. J. Chem. Phys. 88(3):

2057; 1988.

Matsushita, Y. ; Nakao, Y, ; Saguchi, R. ; Mori, K. ; Choshi, H. ; Noda, I.;

Nagasawa, N. ; Chang, T.; Glinka, C. J.; Han . C. C. Phase contrast

matching in lamellar structures composed of mixtures of labeled and

unlabeled block copolymer for small angle neutron scattering.

Macromolecules 21:1802; 1988.

Chang, T. ; Han . C. C.; Wheeler, L. M. ; Lodge, T. P. Comparison of

diffusion coefficients in ternary polymer solutions measured by dynamic

78
light scattering and forced rayleigh scattering. Macromolecules

21: 1870; 1988.

Okada, M. ; Sato, T. ; Han . C. C. Dynamics of concentration fluctuation on

both sides of phase boundary. Inti. Mtg. on Dynamics of Ordering

Processing in Condensed Matter, Kyoto, Japan, August 1987, in press.

Han, C. C.; Dynamics of phase separation in binary polymer mixtures.

Proc. 1st Toyota Conf. on Molecular Conformation & Dynamics of

Macromolecules in Condensed Systems, Inuyama, Japan, September 1987, pp

223=247, 1988.

Howell, B. F. ; Reneker, D. H. Novel methods of preparing polymers for

high resolution transmission electron microscopy. Mat. Res. Soc. Symp.

Proc. 115 : 155 ; 1988

Hunston, D. L. ; Kinloch, A. J.; Wang, S. S. Micromechanics of fracture in

structural adhesive bonds. Proc. 19th Inti. SAMPE Tech. Conf 19: 142; 1987.

Hunston, D. L. ; Kinloch, A. J.; Wang, S. S. Micromechanics of fracture in

structural adhesive bonds. J. of Adhesion, in press.

Hunston, D. L. ; Chai, H. ; VAMAS : A Forum for International Cooperation on

the Development of Composite Standards. Proceedings of 4th Advanced

Composites Conference and Exhibition, ASM. 173; 1988.

Bascom, W. D. ; Hunston . D. L. The fracture of epoxy and elastomermodified epoxy polymers. Treatise on Adhesion & Adhesives 6:, in press.

Bascom, W. D. ; Hunston . D. L. The fracture behavior of epoxy and

elastomer-modified epoxy polymers, Proc. Symp. on Toughened Polymers,

ACS, August 1987, in press.

Beardmore , P.; Hunston . D. L. Industry workshop on polymer composite

processing. NBSIR 87-3686, December 1987.

Gates, R. S.; Jewett

K

L. : and Hsu, S. M. A study on the nature of

boundary lubricating film: analytical method development. STLE. in

press

Krueger, S.; Nossal, R. SANS studies of interacting hemoglobin in intact

erythrocytes. Biophys. J. 53: 97; 1988.

Krueger, S.; Chen, S.-H.; Hofrichter, J.; Nossal, R. SANS studies of

concentrated protein solutions. II. studies of HbA associations, in

press

Lee, A.; McKenna, G. B. Effect of crosslink density on physical aging of

epoxy networks. Polymer, in press.

Mathew, M. ; Brown, W. E. ; Dickens, B.; Schroeder, L. W. Crystal structure

79
of octacalcium bis(hydrogen phosphate) tetrakis (phosphate) pentahydrate

.

J. Crystallographic Spectroscopic Res., in press.

McKenna, G. B.; Crissman, J. M. ; Lee, A. Relationship between failure and

other time dependent processes in polymeric materials. ACS Polymer

Preprints, 1988, in press.

McKenna, G. B.; Flynn, K. M. ; Chen, Y-H. , Mechanical and swelling

behavior of crosslinked natural rubber- consequences of the Flory-Rehner

hypothesis, Polymer Communication, in press.

McKenna, G. B. ; Guenet, J. M. The effects of solvent type on the

concentration dependence of the compression modulus of thermoreversible

isotactic polystyrene gels. J. Poly. Sci., Poly. Phys . Ed. 26: 267; 1988.

McKenna, G. B. ; Guenet, J. M. Aging effects and the dependence of a

modulus on concentration in isotactic polys tyrene/cis-decalin gels. Poly.

Comm. 29:58;1988.

McKenna, G. B. ; Lee, A. Physical aging and the viscoelastic response of

network glasses. Proc. of 7th Inti. Conf. on Deformation, Yield &

Fracture of Polymers, pp. 2/1 -2/4, Plastics and Rubber Institute, April

1988.

McKenna, G. B. ; Rendell, R. W. ; Ngai, K. L. The molecular weight and

concentration dependence of the terminal relaxation time and viscosity of

entangled polymer solution. Macromolecules 20 : 2250 ; 1987

.

McKenna, G. B. Polymer glasses- thermodynamics and kinetics, in

Comprehensive Polymer Science. Vol. 2 : Properties . ed. by C. Booth and C.

Price, Pergamon Press, Oxford, in press.

Guenet, J.-M.; McKenna . G. B. The thermoreversible gelation of isotactic

polystyrene : thermodynamics and phase diagrams. Macromolecules, 2,1., 1752

(1988).

McKinney, J.E.; Antonucci, J.M.; Rupp, N.W. Wear and Microhardness of a

Silver- sintered Glass- lonomer Cement. J. Dent Res 67 ( 5 ) : 831 - 835

,

May

1988

Misra, D. N. Adsorption of phenoxyacetic acid and trans -cinnamic acid on

hydroxyapatite, Symp. on Surfactants in Solution, in press.

Misra, D. N. ; Johnston, A. D. Adsorption of n-phenylglycine on

hydroxyapatite : role in the bonding of a restorative resin to dentin. J.

Biomed. Matls . 21 : 1329 ; 1987

.

Mopsik, F. I.; Kelley, E. F. ; Martzloff, F. D. A review of candidate

methods for detecting incipient defects due to aging of installed cables

in nuclear power plants. NBSIR88-3774, May 1988.

Yeh, T. Y. ; Kelly, R. M. ; Olson . G. J.; Cox, J. C. Significance of cell

fluorescence color of acridine orange stained thiobacillus ferrooxidans

80
Yeh, T. Y. ; Kelly, R. M.; Olson . G. J.; Cox, J. C. Significance of cell

fluorescence color of acridine orange stained thiobacillus ferrooxidans

under epifluorescence microscopy. P. R. Norris, D. P. Kelly, eds . , Biohydrometallurgy, in press. —

Olson, G. J. Recent progress in coal bioprocessing research in the U.S.

scope and areas needing further research. Resources, Conservation and

Recycling, in press.

Olson, G. J.; Brinckman, F. E. ; Jewett, K. L. ; and Thayer, J. S.

Microbial metabolites as agents for reduction of metals to pure metallic

states. Proc. Soc. Mining Engin. , in press.

Schicho, R. N. ; Brown, S. H. ; Olson, g. J. and Kelly, R. M. Probing

coals for non-pyritic forms of sulfur using sulfur-metabolizing

mesophilic and hyperthermophilic bacteria. Proc. EPRI Symp, in press.

Olson, G. J.; Brinckman, F. E. ; Blair, W. R. Methods for the analysis of

organometallic compounds in wastes. ASTM STP 999 : 130 ; 1988

Olson, G. J.; Brinckman, F. E. Microbial metal leaching and resource

recovery processes in: Frontiers in Bioprocessing, S. K. Sikdar, et al .

,

eds., CRC Press, Inc., Boca Raton, FL (1987), in press.

Olson, G. J.; Brinckman, F. E. Bioalkylation in: Inorganic Reactions and

Methods, J. J. Zuckerman, Ed., Verlag Chemie, Berlin, in press.

Cooney, J. J.; Kronick, A. T. ; Olson. G . J: Blair, W. R. ; and Brinckman,

F. E. A modified method for quantifying methyl and butyltins in

estuarine sediments. Chemosphere, in press.

Manders, W. F. ; Be llama, J. M. ; Johannesen, R. B.; Parks . E. J.;

Brinckman, F. E. Characterization of organometallic polymers by 13 C- and

119 Sn-NMR: configurational/compositional triads in poly ( tri -n-butyltin

methacrylate/methylmethacrylate). J. Poly. Sci. Poly. Chem. 25 : 3469 ; 1987

Parks, E. J.; Brinckman, F. E.; Jewett, K. L. ; Blair, W. R. ; Weiss, C. S.

Compounds with signal increases induced by transition metal ions. J

AppI . Organometal . Chem . , in press.

Passaglia, E. Craze and fracture in polymers, J. Chem. Phys . Solids, in

press

Passaglia, E. ; Di Marzio, E. A. Estimation of the amount of non-adjacent

re-entry in polymer crystallization. II. application to once folded n- paraffins. J. Chem. Phys. 87 (8) : 4908 ; 1987

Bundy, K. J.; Penn . R. W. Improvement of metal/bone cement interfacial

strength, J. Biomedical Matls. Res., in press.

Reneker, D. H. ; Howell, B. F. Preparation of polymer molecules for

81
Reneker, D. H. ; Mazur, J. Small defects in crystalline polyethylene,

Polymer, 29:3; 1988.

O'Sullivan, B.; Johnson, P.; Hesby,^R.; Blosser, R. ; Rupp . N. W. ; Pelleu,

G. Bonding strengths of a luting composite resin to dentin using

different bonding systems, J. Pros. Dent. 58: 171; 1987.

Schen, M. A. New polydiacetylenes incorporating mesogenic side chains.

Proc. of SPIE, Inti. Soc. for Opt. Eng., 824:93; 1987.

Schen, M. A.; Chien, J. C. W. ; Lefrant, S.; Perrin, E. ; Mulazzi, E.

Resonant raman scattering of controlled molecular weight polyacetylene.

J. Chem. Phys., in press.

Schreiber, C. T. ; Shem, R. J.; Chow, L. C.; Kingman, A. Effects of

rinses with an acidic calcium phosphate solution on fluoride uptake,

caries and in vivo plaque pH in rats. J. Dent. Res., 67(6):959, June 1988

Smith, L. E. ; Verdier, P. H. Polymer standards, Enc . of Poly. Sci. &

Eng. 12 : 690 ; 1988

.

Stansbury, J.W.; Bailey, W.J. Evaluation of spiro orthocarbonate monomers

capable of polymerization with expansion as ingredients in detal

composite materials. Poly. Mat. Sci. Eng., Proceedings of the ACS

Division of Polymeric Materials, Vol.59, 1988.

Takagi, S.; Chow, L. C.; Yamada, E. M. ; Brown, W„ E. Enhanced enamel f

uptake by monocalcium phosphate monohydrate gels. J. Dent. Res.

66(10) :1523;1987.

Kuriyama, M. ; Dobbyn, R.C.; Takagi . S.; Chow, L. C. Microradiography with

an x-ray image magnifier: application to dental hard tissue. Med. Phys.

14(6) :968;1987.

Dobbyn, R. C.; Kuriyama, M. ; Takagi . S.; Chow, L. C. High resolution

radiography: application to biomedical imaging, Proc. 6th Southern

Biomedical Enginering Conference, Dallas, TX, October 1987.

Tesk, J. A. High temperature dental investments, Book Chapter, in press.

Tesk, J. A.; Anusavice, K. J. Summary of conference on design of dental

prostheses. Dent. Mat. 4:49; 1988.

Engler, R. A.; deRijk, W. G.; Tesk . J. A. and Morris, D. Multidimensional internal setting expansion of a phosphate -bonded casting

investment measured with strain gauges. J. Prosthetic Dent., in press.

Hirano , S.; Tesk . J. A. Hinman, R. ; Argentar, H. ; Gregory, T. Casting of

dental alloys mold and alloy temperature effects, Dent. Matl. 3: 308; 1987.

Tesk, J. A. Review of the paper: casting metals by Kamal Asgar, J. Dent.

Res . , in press

.

82
Hirano, S.; Tesk . J. A. Hinman, R. ; Argentar, H. ; Gregory, T. Casting of

dental alloys mold and alloy temperature effects, Dent. Matl. 3: 308; 1987.

Tesk, J. A. Review of the paper: .casting metals by Kamal Asgar, J. Dent.

Res . , in press

Tesk, J. A.; Brauer, G. M. ; Antonucci, J. M. ; McKinney, J. E.; Stansbury,

J. W. ; Venz, S.; Lee, S.; de Rijk, W. ; Penn, R. W. ; Sugawara, A.; Asaoka,

K. Properties and Interactions of Oral Structures and Restorative

Materials. NBSIR 88-3782, June 1988.

Tesk, J. A. Dental materials and technology research at the National

Institute of Standards and Technology, a model for government -private

sector cooperation. Proceedings of Materials Research Society Symposium

on Biomedical Materials and Engineering, November 30 -Dec. 9, 1987, in

press

Asaoka, K. and Tesk. J.A. Transient and residual stress in dental

porcelain fused- to-metal restorations as affected by the thermal

expansion coefficients of the alloys. Proceedings of Third World

Biomaterials Congress, April 21-25, 1988, Kyoto, Japan, p. 518.

Tomazic, B. B. ; Brown, W.E.; Queral, L. A.; Sadovnik, M. Physicochemical

characterization of cardiovascular calcified deposits. I. isolation,

purification and instrumental analysis. Atherosclerosis 69:5; 1988.

Perez, E. ; VanderHart . D. L. A

13 C CP-MAS NMR study of irradiated

polyethylene. J. Poly. Sci. Poly. Phys . , 26:1979; 1988.

Perez, E. ; VanderHart . D. L. ; McKenna, G. B. NMR study of gels of

isotactic polystyrene and cis- or trans -decalin. Macromolecules, 21, 2418

(1988).

Vogel, G. L. ; Chow, L. C.; Carey, C. M. ; Brown, W. E. Microelectrode

techniques for the analysis of oral fluids. J. Dent. Res. 66(11): 1691;

1987.

Wang, F. W. ; Lowry, R. E.; Fanconi, B. M ; Heiweil, E. J. Fluorescence

properties of a rod- like polymer and its model compound. Poly. Matl. Sci.

Eng. 57:336;1987.

Wang, F. W. ; Lowry, R. E.; Pummer, W. J.; Fanconi, B. M.; Wu, E.-S.

Fluorescence monitoring of viscosity and chemical changes during

polymerization in photophysics of polymers (Eds., C. E. Hoyle and J. M.

Torkelson) , ACS, Wash. DC, Chapter 33, pp. 454, 1987.

Wang, F. W. ; Bur, A. J.; Lowry, R. E. ; Fanconi, B. M. Fluorescence

Monitoring of Polymer Processing. Poly. Matl. Sci. Eng., in press.

Waterstrat, R. M. ; Kuentzler, R. Stabilization of a-Mn structures in new

ternary chi-phases. J. Less-Comm. Metals, in press.

83
Wu, W. L; Bauer, B. J. Network structure in epoxies. Deformation

mechanism in epoxies. Macromolecules 21 (2) : 457 ; 1988

.

Wu, W. L. ; Hunston, D. L. ; Yang, H. ; Stein, R. S.; Epoxy network

structure 4, a neutron scattering study of epoxies swollen in a

deuterated solvent. Macromolecules 21 (3) : 756 ; 1988

.

Wu, W. L. ; McKinney, J. E. Glass transition temperature in dental

composite resins. J. Dent. Res., in press.

M. Benmouna, H. Benoit and W. Wu . Scattering in multiple -component

system, accepted in Polymer.

W. Wu and J.R. Prahinski, Some Theoretical Results of Swelling in Fiber

or particle filled polymers. Polym. Eng. & Sci„, in press.

Coleman, B.D.; Zanas . L. J

.

: A phenomenological theory of the influence

of strain history on the rate of isothermal stress relaxation. J. of

Rheology, in press.

Zapas , L. J.; McKenna, G. B. , Brenna, A. An analysis of the corrections

to the normal force response for the cone and plate geometry in single

step stress relaxation experiments. J. of Rheology, in press.

84
Technical and Professional Committees : Leadership Activities

Academy for Dental Materials

J. A. Tesk, Member, Executive Committee

Academy of Operative Dentistry

N. W. Rupp, Past President

Adhesion Society

D. L. Hunston

Chairman 1989 Annual Meeting

Alpha Chi Sigma

G. M. Brauer, Member, Awards Committee

C, M. Carey, President, American University Chapter

American Academy of Gold Foil Operators

N. W. Rupp, President

American Academy of Implant Dentistry

J. A. Tesk, J. Oral Implantology , Academic Referee

American Association for Dental Research/Intemational

Association for Dental Research

L . C . Chow

Member, Fellowship Committee

E. A. Eanes

Member, Science Awards Committee

Chairman, Biological Minerlization Award Subcommittee

Councilor, Mineralized Tissue Group -AADR

Member, Scientific Awards Committee

J. A. Tesk

Treasurer, Dental Materials Group

American Association of Dental Research - Washington Section

J. M. Antonucci, Secretary -Treasurer

J. M. Antonucci, Member, Board of Managers

L. C, Chow, President

American Chemical Society

G. Mo Brauer

Alternate Councilor

C. C. Han

Co-Chairman for the Symposium on Polymer Diffusion, 1987

F. W. Wang

Co-Chairman for the Symposium on Introduction to

Fluorescence Characterization of Polymers

85
American Dental Association

R . L . Bowen

Member, Biomedical Research Support Grant Committee

American National Standards Committee, MD 156, Dental Materials,

Instruments, and Equipment

R . L . Bowen

Secretary, Subcommittee on Biological Evaluation of

Dental Materials

Member, Subcommittee on Direct Filling Resins

G . M. Brauer

Chairman, Subcommittee on Denture Materials Specifications

Member, Dental Materials, Instruments and Equipment

Member, Zinc Oxide -eugenol and Modified ZOE Cements Subcommittee

Member, Color Stability of Resins Subcommittee

N. W. Rupp

Chairman, Group I Restorative Materials

Member, Subcommittee #1 - Alloy for Dental Amalgams

#6 - Mercury for Dental Amalgams

#29 Fissure Sealants

#43 - Dispersers for Alloy & Mercury

#55 - Electrically Powered Amalgamators

J. A. Tesk

Member, USA TAG for ISO TC 106

American Physical Society

G . B . McKenna

Division of High Polymer Physics

American Society for Metals

R. M. Waterstrat

Member, Alloy Phase Diagram Data Committee

ASM International

R. M. Waterstrat, Fellow

American Society for Testing and Materials (ASTM)

G„ M. Brauer

Member, Executive Committee, F-4 Medical and Surgical

Materials, and Devices

Chairman, Polymeric Materials Section

F. E. Brinckman

Member, E~34 Occupational Helath and Safety

Member, E-47 Biological Effects and Environmental Fate

Member, E-48 Biotechnology

Member, E-48. 03. 07 Subcommittee on Ore Bioleaching... . S . S . Chang

Member, D37 Thermal Measurements

D37.01 Test Methods

D37.05 Thermophysical Properties

86
C. M. Guttman

Member, D20.30 Thermal Properties

D20.70 Analytical Methods

E-37 - Subcommittee on Thermal Analysis

Chairman, Task Group on Purity Standards and Methods

D. L. Huns ton

Member, D30 High Modulus Fibers & their Composites

G . B . McKenna

Member, D-ll Rubber and Rubber- like Materials

Member, E-9 Fatigue

G. J. Olson

Member, E-46 Biotechnology

Task Group Chairman, E-48.03.07 Subcommittee on Bioleaching Ores

Member, E-47 Biological Effects and Environmental Fate

L. J. Zapas

D-2 Petroleum Products and Lubricants

Member: D2.07 Flow Properties

D2.07A Newtonian Viscometry

Center for Adhesion Science, Virginia Polytechnique Institute

D. . Huns ton

Member, External Advisory Board

Center for Composite Materials and Structures, Michigan State University

D. L„ Huns ton

Member, External Advisory Board

Chemical Society of Washington

J. M. Antonucci

Member, Board of Managers

G. M. Brauer

Chairman, Public Relations Committee

Comite International Permanent pour La Recherche Sur La Preservation des

Materiaux en Milieu Marin (COIPM)

F. E. Brinckman, NBS Delegate

W. R„ Blair, NBS Delegate

Dental Materials Journal

J. A. Tesk, Editorial Board

DoC Small Business Innovation Research Program

M. G„ Broadhurst

Contracting Officers Technical Representative

Federation of Materials Society

D. L. Huns ton

Organizing Committee 1988 Meeting on National Materials Policy

87
Gordon Conference: Calcium Phosphates

L. C. Chow

Co -chairperson, 1989

Institute of Electrical & Electronic Engineers (IEEE)

Conference on Electrical Insulation & Dielectric Phenomena

A. S„ DeReggi

Member, Board of Directors

International Conference on Polymer Crystals

F . A . Khoury

Member, Advisory Board

International Council on Alloy Phase Diagrams

R. M. Waterstrat

Member

International Journal of Adhesion & Adhesives

Dc L„ Huns ton

Member of International Advisory Editorial Board

International Journal of Applied Organometallic Chemistry

F, Eo Brinckman

Member of Editorial Board

International Journal of Chemical Speciation and Bioavailability

F. Ee Brinckman

Member of Editorial Board

International Standards Organization

TC106, Dental Materials and Devices

N . W . Rupp

Member, Restorative Materials

Chairman, SC. 01, U.S. Delegation

Chairman, ATG7 , Alloys for Dental Amalgams

SC6 WG5 Electrically Powered Amalgamators

International Symposium on Electrets

G. T. Davis

Member of Program Committee

Macromolecules

D. L. VanderHart

Member, Editorial Review Board

Metallurgical Society AIME

R. M. Waterstrat

Member, Committee on Alloy Phases

National Academy of Science/National Research Council

Organotin Research Panel

F. E. Brinckman, Member

88
National Information Standards Organization (NISO)

E . J . Parks

Member, Committee on Environmental Conditions for Storage

of Paper- Based Library and Archive Collection

National Institute Dental Research

J. M. Antonucci

Special Review Committee for Research Centers of

Oral Biology ADHOC Review

Special Study Sections for Small Business Innovative Research

(SBIR) Grant Applications, Reviewer for SBIR Site Visit

National Institutes of Health Library Committee

E. 0. Eanes, Member

National Institue of Standards Intelligent Materials Processing Workshop

A. J. Bur, Chairman

NIST-Dental Materials Academy Conference on Modem Instrumentation

and Analysis Methods

J. A. Tesk, Chairman

National Science Foundation Advisory Board

Regional NMR Facility at Colorado State University

D. L. VanderHart

Office of Naval Research

J. M. Antonucci

Bioengineering for Materials Application (BEMA) Research Program

Review Meeting, 1987

Member of the Molecular Biology Program/Office of Naval Research

Oversight Panel

Office of Science and Technology Policy

D. H. Reneker

Executive Secretary, Committee on Materials (COMAT)

Office of Technical Assessment (U,S„ Congress) Panel on Archival

Paper Recovery and Preservation

E. J. Parks, Consultant 1987-1988

Plastics Institute of America

D. H. Reneker, Board of Directors

Polymers

P.

Division Editorial Committee

H. Verdier, Chairman

Polymers Gordon Conference (West)

E. A. Di Marzio, Vice-Chairman & Chairman Elect, 1988-89

89
Scientific Affairs Division, North Atlantic Treaty Organization

F. E. Brinekman

G. J. Olson

Consultants (1988) to European Community Methylmercury

Research Group

Society of Rheology

G . B . McKenna

Member, Committee on Education

Member, Executive Committee

D. L. Hunston

Member, Committee on Education

Member, Site Selection Committee

U* S. Air Force

N . W . Rupp

Surgeon General's Civilian Consultant on Dental Materials

U.S. Yugoslav Joint Scientific and Technological

Cooperative Program

W. E. Brown

NBS Member

VAMAS

C . C. Han

Member, Technical Working Party on Polymer Blends

D. L* Hunston

Member, Technical Working Party on Polymer Composites

World Biomaterials Congress

J. Ac Tesk, Chairman, Session on Dental Materials

90
Industrial and Academic Interactions

Industrial

The Research Associate agreement with IMASS Corporation to transfer the time

domain spectrometer technology for commercialization has resulted in an

instrument which is offered for sale by the company. Capabilities of the

instrument are equivalent to those of the spectrometer developed by NIST.

A Research Associate agreement with SICPA, Virginia continues in effect to

transfer piezoelectric and pyroelectric polymer technology for possible

addition of polymer sensors to their product line.

The Research Associate agreement with Westinghouse has been renewed to transfer

measurement techniques for compliant piezoelectrics.

In collaboration with Chronos Research Laboratories, preliminary experiments

have been performed on the laser- induced release of electrical energy from

polarized films of piezoelectric polymers.

Over twenty industrial representatives from polymer processing companies were

invited to the NIST Intelligent Materials Processing Workshop held on August

31 -September 1, 1988. Those attending the workshop were from a cross section

of the polymer processing industry including resin manufacturers, processors,

machinery manufacturers, and end users. The workshop presented an excellent

environment for the direct interchange of ideas and technological information

between NIST and the polymer processing industry.

A recently inaugurated Research Associate collaboration with Technical

Assessment Systems, Inc., installed and collaboratively demonstrated with

Polymers Division staff, the first applications of ultratrace biosensing of

organometals by in vitro computerized multilaser spectrophotometry and selected

mutant strains of a bacterium. These results set the stage for field testing

of a potentially new measurement system, applicable to relating molecular

topologies of technological materials quantitively to both adverse and

beneficial biotic responses.

Bioreduction of gold and other precious metals to pure metallic microparticles

by volatile metabolic products was demonstrated. Reaction intermediates,

morphologies and purity of particles were evaluated by scanning electron

microscopy-energy dispersive x-ray microanalysis techniques. The work

attracted an invitation from the Metallurgical Society and American Institute

for Mining Engineering to present a talk on the subject at the upcoming

International Symposium on Biotechnology in Minerals and Metals Processing.

Several platinum group metals and catalyst industrial firms have now indicated

collaborative interest.

Standard reference materials have been issued for polyethylene resins of the

sort used in natural gas distribution systems. Production of the SRM was

supported by the Gas Research Institute which is also funding studies of the

effects of processing polyethylene resins into pipes and fittings. The

91
reference materials will facilitate test method development, standardization of

test methods, and inter -laboratory comparisons of test data.

Discussions are in progress with members of ASTM D-20 subcommittee on thermal

methods on the production of a polypropylene SRM for which the melt flow rate

will be certified. This standard reference material will facilitate

calibration of melt flow apparatus described in the voluntary standard method

ASTM D-1238.

The Institute of Paper Chemistry, Appleton, WX. is collaborating with NIST in

the study of the effects of diethyl zinc (DEZ) treatments on cellulonic

materials. The Library of Congress funds the work in support of its program to

use DEZ to enhance preservation of archival materials

.

A joint research project on advanced thermosets has been initiated between NIST

and Interez. High performance polymeric composites call for matrix resins with

a high glass transition temperature and a high fracture toughness. Bisphenol A

dicyanate (BADCy) from Interez is a major candidate for this need. Partially

deuterated BADCy has been prepared by Interez, and the network structure of

this material is being characterized by NIST using neutron scattering. It is

of interest to compare the network structure for this new type of resin to that

obtained for the epoxy systems previously studied in the NIST program.

Joint polymer blends related projects are underway with several large

companies. These include Exxon, IBM, eastman Kodak, Hercules, Mobil Chemical

and General Motors. The work will focus on equilibrium phase behavior and

phase stabilization problems for specific polymer blends with Exxon, IBM and

Eastman Kodak, and on the domain orientation, fiber structure and blends

morphology with Mobil Chemical, Hercules and General Motors. The newly

constructed 10 meter SAXS instrument has also been used by Mobil Chemical,

Hercules and General Motors for structural characterization on various

polymers

.

Contacts with the dental industry and profession have remained strong. Monthly

articles have been submitted to the American Dental Trade Association, the

American Association of Dental Manufacturers and the American Dental

Association to keep them abreast of recent developments. An invited lecture

was delivered to the "Cal - Lab" group of dental laboratories on future dental

laboratory processing methods. Research associate agreements with Dentsply

International and Astron Corporation remain enforce and the latter has

introduced a significantly new product as a result of its work at NIST.

Assistance in materials or funding was supplied to NIST or the American Dental

Association Health Foundation Research Associates at NIST by Pentron

Corporation, Morita Corporation, the Colgate-Palmolive Company and Tokuyama

Soda Company.

Industrial/Academic

The piezoelectric properties and molecular orientation of deuterated vinylidene

fluoride polymers and copolymers supplied by AT&T Laboratories have been

investigated in a cooperative effort between NIST and Washington University in

St. Louis.

92
Metabolic products of fungi capable of solubilizing phosphorus from iron ore

were identified in collaborations established under the NIST Steel Program.

Tests with U.S. industrial iron ore concentrates showed the bioproducts,

consisting of oxalic acid and other organic acids, rapidly (<10 min) removed

over 50% of phosphorus from the ore and potentially offer a novel bioprocess

for domestic iron ore beneficiation. More detailed evaluation of biological

dephosphorization and potential on-site scale-up testing with Cleveland Cliffs

Iron Co. and Michigan Technological University is planned.

The desulfurization of coal by extremely thermophilic bacteria (100°C) was

demonstrated in a joint NIST- Johns Hopkins University project supported by the

Electric Power Research Institute. The use of microorganisms to bioassay

sulfur species in coal was also demonstrated. These data provide information

on the types and accessibilities of forms of sulfur in coal and also provide

novel processing options for coal beneficiation.

Researchers from Exxon Research and Development Company, Hercules, Inc. and the

University of Pittsburgh are collaborating with scientists in the Polymers

Division in characterization of dilute solution and melt properties of cyclic

macromolecules. A_manuscript has been prepared on the work which addresses

validation of current models of macromolecular dynamics.

A joint NIST-Polaroid-Kyoto Institute of Technology (KIT) project has been

initiated to determine the structure of polyvinyl alcohol (PVA) gel, more

specifically the structure of alkaline gel. This type of gel is the precursor

of high performance PVA fiber, and the properties of the fibers depend on the

structure of the gel. Both gel and fiber samples are being provided by KIT and

Polaroid while NIST is characterizing the structure of these materials.

A joint NIST-Gencorp-University of Kyoto project will address microstructure

and isotope effects in rubber/rubber blends. Miscibility and phase diagrams

will be determined and mechanical blending/phase separating processes will be

determined for immiscible rubber/rubber pairs. The desired information is

particularly valuable to the rubber industry.

Academic

Dr. Naoto Tsutsumi from Kyoto Institute of Technology is working at NIST during

his sabbatical leave. He is studying changes in the spectra of molecular

probes to measure internal electric fields in polymers.

Collaboration continues with the University de Nantes, France and the

Universitas di Milano, Italy to explore the use of Resonance Raman Scattering

to determine the effective conjugation lengths in polyacetylenes of different

molecular weights.

In collaboration with IMSE guest scientists from Universities of Maryland and

District of Columbia, a complete NBS computer program has been successfully

demonstrated with capability to assess energetically likely molecular

configurations and van der Waal "total surface area" (in A02) for quantitative

structure - activity relationships (QSARs) , applicable as independent predictors

93
for both physicochemical and biological properties. With both ongoing NBS

metals bioprocessing and external transfer of NIST QSAR data or methods, joint

published results demonstrate ongoing metals solubility, chromatographic

partitioning, biouptake and toxicity.— .applications attracting substantial

domestic and international collaborative prospects.

We determined experimental protocols and successfully demonstrated with the new

NIST Cold Neutron Source application of small angle neutron scattering plus xray scattering techniques to characterize metal particles in and on living

cells in collaboration with Professor R.P. Blakemore of the University of New

Hampshire,. Conditions necessary to conduct kinetic metal bioprocessing

experiments have been established.

Collaborative work’ with J. Shibata, University of Tennessee, is being carried

out for the purpose of employing fluorescence photob leaching and fluorescence

quenching to measure polymer processing parameters.

Epifluorescence microscopic imaging (EMI) methods in combination with metalspecific fluorogenic ligands was used to demonstrate bioaccumulation of yttrium

by bacteria and aluminum by plant material in collaboration with University of

Maryland students. These demonstrations illustrate the potential of the method

for trace monitoring of metals bioprocessing and mapping resident metallic

moieties in biogenic or synthetic polymer composites.

A novel mechanism of microbial resistance to chromium (VI) was demonstrated in

collaboration with Professor F. Baldi of the University of Siena, Italy. A

chromium* resistant yeast isolated from tannery wastes was shown to exclude Cr

from the cell. Further characterization of mercury resistance and

biotransformations by aerobic bacteria isolated from Italian cinnabar deposits

also showed that mercury resistance is not related to biomethylation. In this

connection, NBS staff have been invited to a NATO- European Community meeting to

provide guidance and transfer NBS measurement methods, standards and mechanisms

involving the origin and fate of methylmercury in the Mediterranean.

The bioaccumulation of gallium by microbial cells and gallium binding by

exocellular biogenic iron macrothelators , or siderophores , was demonstrated as

part of an Air Force supported project to develop novel processes for gallium

recovery. University of Maryland students and Center for Analytical Chemistry

scientists have collaborated with us in isolating and characterizing the

siderophore structure and studying iron and gallium binding phenomena by NMR.

We have been invited to discuss these macroligand and other of our metal

bioaccumulation studies at the 1989 International Symposium on Metallurgical

Processes for the Year 2000 and Beyond.

A joint program with Montana State University, funded by the Strategic Highway

Research Program, investigates the chemical and physical structure of asphaltic

cements, in particular the time and temperature dependence of molecular

aggregation. Solution and solid state nuclear magnetic resonance techniques

are used in this work.

A joint NIST-Colorado State University project on molecular composites has been

started as part of a large DARPA program. The main thrust in this project is

94
to determine whether the rigid rod molecules that form the bases for a

molecular composite are dispersed on a molecular level in the matrix composed

of flexible chains. It is believed that maximum mechanical properties can be

achieved with this optimum dispersion. Prof. J. K. Stille of Colorado State

University is providing the materials, and NBS is developing the methodology

for characterizating the degree of dispersion.

A joint program with Drs. Ron Eby and Herzl Chai of Johns Hopkins University is

investigating the use of adhesive joint fracture tests as a method to simulate,

in a controlled way, interlaminar fracture in a composite. Johns Hopkins is

performing the fracture experiments while NIST is supplying expertise in the

analysis of crack- tip deformation zone effects when the zone is constrained in

a thin bond line or a composite. The work could lead to a new fracture test

with important advantages over tests performed with composites.

The failure behavior of toughened adhesives is the subject of cooperative work

with Dr. A. J. Kinloch of Imperial College (London) and Dr. S. S. Wang of the

University of Illinois. The program is experimentally characterizing the

growth of the crack- tip deformation zone during loading and comparing the

results with predictions from finite element models. Such studies are a first

step in developing failure criteria for these systems.

Collaborative programs in the area of blends include work on single chain

conformations and diffusion with the Universities of Wisconsin and Minnesota,

and an ongoing NSF/JSPS- sponsored program on block copolymers in microphase - separation systems with Nagoya University.

Studies on the development of residual and transient stress in dental glass

coated metal stress are being pursued jointly with Tokushima University, Japan

and a manuscript on the effects of various elements on the casting of dental

alloys has been co-authored with a researcher from Tokyo Medical and Dental

University. Group members also serve on study sections for grants from the

National Institute of Dental Research and the National Cancer Institute. Two

members serve as consultants to the U. S. Navy. A collaborative study with

Loyola University on fluoride caries inhibition is underway. guest Scientists

from the Rudjer Boskovic (Yugoslavia) and Nihon University (Japan) have been

working on calcium phosphate chemistry Calcium phosphate cements are being

developed cooperatively with scientists at Taiwan University. Collaborative

work with a University of Maryland researcher is in progress on statistical

methods to predict results of clinical studies in progress and plasma

sterilization of instruments is being pursued with the U. S. Navy.

95
Associated Activities

Invited Talks

Division personnel presented a total of 88 invited talks on research activities

at the following types of organizations and symposia: industrial laboratories,

12; international symposia, 14; universities, 27; topical symposia, 10;

national and government laboratories, 5; professional society meetings, 17; and

Gordon Conferences, 4.

SUMS

Certificates have been issued for two polyethylene SUMS (1496 and 1497) which

are similar id composition to polyethylene resins used in natural gas

distribution systems. These SRMS are expected to facilitate test method

development, standardization of test methods, and interlaboratory comparisons

of test data.

Certification of SRMS, n-t-butyl 2-benzothiazole sulfanamide, a rubber

compounding SRM, was completed. The rubber industry uses rubber compounding

SRMS in ASTM test protocols for qualifying rubber materials.
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HBS-1MA twav. a-«o> U.s. DOT. or COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION Of>

REPORT NO.

NISTIR 88-3842

2. Performing Organ. Report No. 3. Publication Date

NOV. 1988

4. TITLE AND SUBTITLE

Polymers Division; Technical Activities 1988

5. AUTHOR(S)

L. E. Smith and B. M. Fanconi

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

I.- Type of Report & Period Covered

Annual Report

10/1/87 - 9/30/88

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Institute of Standards and Technology

Institute for Materials Science & Engineering

Polymers Division, Gaithersburg, MD 20899

10. SUPPLEMENTARY NOTES

HH Document describes a computer program; SF«!85, FIPS Software Summary, is attached.

IX. ABSTRACT (A IQQ^word or less factual summary of most significant information . If document includes a significant

bibliography or literature survey, mention it here

)

Technical Activities of the Polymers Division for FY 88 are reviewed. Included

are descriptions of the 6 Tasks ©f the Division, project reports, publications,

and other technical activities.

12. KEY WORDS (Six to twelve entries ; alphabetical order

;

capitalize only proper names ; and separate key words by semicolons)

National Institute of Standards and Technology; Polymers Division; Review;

Technical Activities

13. availability

ns Unlimited

For Official Distribution. Do Not Release to NTIS

”TM‘ “ Order From Suoerintendent of Documents, U.S. Government Printing Office. Washington, D.C.

20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

119

15. Price

$18.95

USCOMM-OC S043.P30