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NISTIR 88-3892

In SITU Fluorescence

Monitoring of the

Viscosities of

Particle-Filled

Polymers in Flow

A. J. Bur, F. W. Wang, A. Lee, R. E. Lowry, S. C. Roth, and T. K. Trout

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

Polymers Division

Gaithersburg, MD 20899

November 1988

Annual Report to

The Office of Naval Research

Arlington, VA 22217

Contract No. N00014-86-F-01 15

R. S. Miller, Contract Officer

Research supported by SDIO Innovative Science and Technology Office managed

by the Office of Naval Research.

0 f c< V N==^

75 StimuLattfiQ Amenc* • Ptogr*i»

NISTIR 88-3892

In SITU Fluorescence

Monitoring of the

Viscosities of

Particle-Filled

Polymers in Flow

A. J. Bur, F. W. Wang, A. Lee, R. E. Lowry, S. C. Roth, and T. K. Trout

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

Polymers Division

Gaithersburg, MD 20899

November 1988

National Bureau of Standards became the

National Institute of Standards and Technology

on August 23, 1988, when the Omnibus Trade and

Competitiveness Act was signed. NIST retains

all NBS functions. Its new programs will encourage

improved use of technology by U.S. industry.

Annual Report to

The Office of Naval Research

Arlington, VA 22217

Contract No. N00014-86-F-01 15

R. S. Miller, Contract Officer

Research supported by SDIO Innovative Science and Technology Office managed

by the Office of Naval Research.

U.S. DEPARTMENT OF COMMERCE

C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

Ernest Ambler, Director

IN SITU FLUORESCENCE MONITORING OF THE VISCOSITIES OF PARTICLE- FILLED

POLYMERS IN FLOW

A.J. Bur, F.W. Wang, A. Lee, R.E. Lowry, S.C. Roth, and T.K. Trout

U.S. Department of Commerce

National Institute of Standards and Technology

(formerly National Bureau of Standards)

Polymers Division

Gaithersburg, MD 20899

ABSTRACT

Work during FY88 has focused on three areas: the chemical synthesis of a

polymeric chromophore ; the design of experiments to measure fluorescence

anisotropy and non-Newtonian viscosity as a function of shear rate; the design

of a fiber optic velocity sensor; and, measuring the quality-of -mix of a two

component material using a fluorescence microscope. Significant results from

these areas of work are: (a) a polymeric chromophore, consisting of anthracene

covalently bonded to polybutadiene, has been synthesized and characterized by

gel permeation chromatography and infrared observations. The number average

molecular weight is 12,000 which is above the entanglement molecular weight for

polybutadiene; (b) experiments using the polymeric chromophore as a dopant in a

Newtonian fluid, very low molecular weight polybutadiene, show that

fluorescence anisotropy correlates with the viscosity, i.e. it remains constant

as a function of shear rate; and, (c) using a fluorescence microscope, we have

measured optical transmittance and near neighbor distances between particles in

a matrix/particle mixing experiment and correlated these data with fluorescence

intensity fluctuations.

1
INTRODUCTION

Fluorescence spectroscopy is a tool which is used in many fields of science to

1 obtain both microscopic and macroscopic information. Its application to

propellant processing is a relatively new endeavor which requires significant

development in order to realize the full potential of the technique. From a

large body of fluorescence spectral data in the literature and from work

carried out previously in this laboratory, we have conceptually established the

methods by which we can use fluorescence spectrometry to measure processing

parameters such as the quality of mix of ingredients, non-Newtonian viscosity,

molecular orientation, velocity and velocity gradient, flow instabilities such

as wall slip, and intersegmental mixing at the molecular level.

The technique involves the excitation of fluorescent chromophores and the

subsequent monitoring and analysis of the fluorescence spectra. Since polymer

binders are not naturally fluorescent, it is necessary to dope the processing

ingredients with a low concentration of fluorescent chromophores which are

added as separate entities or chemically bound to the binder. A chromophore is

chosen in accordance with its sensitivity to the processing parameter of

interest. To monitor several processing parameters, a separate chromophore for

each parameter will be employed. Fluorescence spectra can be obtained with

extremely low concentrations of chromophore in the binder (10' 4 to 10 6 molar)

and, therefore, their presence does not affect the materials properties of the

final product.

The ultimate application is to use fluorescence spectroscopy as an on-line

2
non -destructive probe for real-time monitoring of processing parameters.

Optical fibers can be employed to transmit and receive optical energy to and

from monitoring sites in the processing equipment. Optical energy which is

sent to the monitoring site excites nearby chromophores which respond by

radiating characteristic spectra. From an analysis of the spectra, processing

conditions at the probe site can be determined.

Our research goals over the past year have been: (a) to synthesize a polymeric

chromophore which can be used in the fluorescence anisotropy/non-Newtonian

viscosity experiments, (b) to complete the development of fluorescence

anisotropy equipment and to utilize this equipment to measure fluorescence

anisotropy and non-Newtonian viscosity simultaneously, and, (c) to continue the

quality-of -mix experiments using a fluorescence microscope to quantify the

spatial distribution of particles in a binder/particulate specimen as a

function of mixing. In the text below, the results and discussion of each of

these work areas will be presented independently.

A. Synthesis of a Polymeric Chromophore

Background

In order to observe polymer materials properties, such as non-Newtonian

viscosity, from fluorescence spectroscopy observations, it is necessary to use

2

a chromophore which is covalently bonded to the polymer backbone. Many

fluorescent dyes are available commercially, but all are low molecular weight

species and do not fit the criteria for our experimental program. The

polymeric chromophore which we have designed is derived from a bifunctional

anthracene which is covalently bonded to polybutadiene so that the

3
f luorescently active anthracene resides at a central position on the polymer

main chain.

Results

The chemical synthesis is shown in Figure 1. Starting with 9,10 dicarboxyl

terminated anthracene, which is converted to anthracene dimethanol, we

covalently bond the anthracene to a dicarboxyl terminated polybutadiene via an

esterification reaction. The number average molecular weight of the starting

polybutadiene was 6000. The synthesized product was characterized using gel

permeation chromatography (GPC) and infrared analysis. Infrared spectra showed

that: (a) the reaction to convert the dicarboxyl anthracene to anthracene

dimethanol yielded the desired product; and, (b) the esterification reaction to

covalently bond anthracene to the polybutadiene proceeded as planned. The

conversion of the dicarboxyl terminated anthracene to dimethanol anthracene was

seen in the elimination of the carboxyl absorption at 1280 cm

-1 and the

creation of the C-0 stretch of the alcohol. Confirmation of the esterification

reaction was obtained from the observation of the creation of the ester

carboxyl line at 1734 cm

-1

.

The GPC trace of the polymeric chromophore is shown is Figure 2 where we have

plotted the GPC detector output versus the elution volume. From this plot, we

show that the product, polybutadiene + anthracene, has a molecular weight which

is approximately twice that of the starting material and its molecular weight

distribution is somewhat broader. Analysis of the data shows that the number

average molecular weight of the product is approximately 12,000 and its weight

average is approximately 24,000. Referring to Figure 1, we conclude that

n — 1, i.e. there is one anthracene per polymer chain and it is positioned in

4
the center of the main chain. The polymeric chromophore is called a labelled

polybutadiene and it is being used in the molecular orientation /non-Newtonian

viscosity experiments.

B. Fluorescence Anisotropy and Molecular Orientation

Theoretical Background

The relationship between fluorescence anisotropy and molecular orientation has

3-5

been examined in model development by several authors. We consider a

fluorescent chromophore, depicted in Figure 3, possessing a molecular axis, M,

which is oriented at angles 6 and <f> with respect to the laboratory frame of

reference. Here, 0 is the azimuthal angle and, for our experiments, z is the

direction of flow. The objective of the model calculations is to establish a

relationship between average orientation moments, cos 2 $ and cos^, and the

measured fluorescence anisotropy. The usual definition of the anisotropy, r,

is given as

( 1 )

where Ivv is a measured fluorescence intensity with vertically oriented

excitation polarizer and emission analyzer, Ivh is the intensity with vertical

polarizer and horizontal analyzer, and I t is the total light intensity. In the

text below, we will use other combinations of vertically and horizontally

oriented polarized light to define an alternative anisotropy, r '

.

We establish a molecular coordinate system, shown in Figure 4, where the

molecular axis M is directed along the c axis and a and e are the absorption

and emission dipoles at angles a and e with respect to M. In general, a and e

are non-zero and unequal, but for anthracene, the chromophore of interest here,

5
a = 0 and e it 0. The relationship between observations in the laboratory frame

of reference and the molecular frame of reference is obtained by making

coordinate transformations which project a and/or e onto the laboratory frame

of reference. The fluorescence light intensities are determined in accordance

with the directions of the polarizer and analyzer vectors P and A.

l\ Following the development of Chapoy and DuPre, one assumes that the

orientation distribution function of the chromophores , f(0), can be expressed

as a sum of Legendre polynomials which, in general, depend on 6 and <f>but for

the case of uniaxial flow along the z direction, we assume axial symmetry so

that the distribution is independent of <f>Since f(0) = only the even

polynomial terms are present. The normalized distribution function is

expressed as

J

1 f(«)d(cos e) = 1. (2)

-

The normalized fluorescence intensity is given by

hj =kC;

o"

M

ai

M

ej

f(S)sln' d

^

(3)

where I i j

is the emitted fluorescence intensity which results from an

excitation light source polarized along the laboratory i axis and which passes

through a polarization analyzer oriented in the direction of the laboratory j

2 2

axis. Ma

and Mej are the squares of the absorption and emission vectors which

have been projected onto the laboratory axes i and j respectively via a

coordinate transformation matrix, and f(0) is the angular distribution

function. We have

6
Mg i (4) 2 = (a-0-Pi) 2

and

(5)

where 0 is the transformation matrix,

0

cos8cos<t> cos#sin<£ -sin#

-sin<^> cos^ 0

sin0cos<^> sin0sin$ cos#

( 6 )

Equations 3 through 6 express the physical sequence of events for light

absorption and fluorescence emission. The absorption vector is brought into

coincidence with a component of the polarized excitation light via the

transformation operation of equation (4) and the reverse occurs during emission

via equation (5)

.

The integrations of equation (3) yield a 3x3 matrix whose components are light

intensities for various combinations of and . Having evaluated the matrix,

one can then calculate anisotropies in accordance with equation (1) where Ivv

becomes I llf I 22 or I 33 and I vh becomes one of the off-diagonal terms. For

example, when a = 0 and e = 0, i.e. absorption and emission dipoles lie along

the direction M, then vertically oriented light will be absorbed in proportion

to cos 2 9 . The emission, which is viewed through a vertical analyzer, is also

proportional to cos2

6 . Equation (3) becomes an integral over all space of

cos k 8 weighted by the orientation function f(0) resulting in I 33 = cos 4 8 .

For anthracene, a = 0 , e 9

* 0, and 5^0, where 5 has been defined in Figure 4,

4

Chapoy and DuPre have evaluated the following matrix:

7
/§ cos2 6 sin4

fl + Tiff sin 2 8 (3 sin 2 0 cos2 0 + sin2 0)

I = | 4 cos2 6 sin 4 # + rg s in 2 6 (sin 2 # cos2 # + 3 sin 2 #)

\£ cos2 5 sin 2 # cos2 # + i sin2 8 (cos2 # + cos4 #)

I cos2 5 sin4 # + Tiff sin2 8 (si n

2 # cos2 # + 3 sin2 #)

§ cos2 8 sin4 # + t^ sin2 8 (3 sin2 # cos2 # + sin2 #)

i cos

2 5 sin2 # cos

2 # + i sin2 8 (cos2 # + cos4 #)

i cos2 8 sin2 # cos2 # + i sin2 8 sin4 # \

£ cos2 5 sin2 # cos2 # + j sin2 6 sin 4 #

) cos2 6 cos4 # + i sin2 5 sin2 # cos2 # /

(7)

We note that the matrix contains orientation moments cos2

9 and cos 4 9 as well as

the term cos2 6 which is a molecular property and does not depend on the

orientation. The value of cos2 5 is obtained from a separate experiment; its

value for anthracene is 0.733.^ A separate measurement of cos 2 8 for the

labelled polybutadiene will be carried out in the future. In general, two

independent measurements of anisotropy must be made in order to calculate

cos 2 9 and cos 4 9 .

In practice we will use a single optical fiber to excite and receive the

fluorescence. The design consists of an optical fiber which is inserted into

the wall of a processing machine flush with the inside surface and used to

probe the fluorescence in the near neighborhood. Figure 5 is a schematic

representation of the physics of the situation, i.e. excitation light polarized

in the z or x direction propagates in the positive y direction and emission is

observed along the y direction with the analyzer oriented in the z or x

directions. Anisotropies r and r' are

r

I - I zz zx

I +21

zz zx

+ 21

31

( 8 )

8
and

r

' =

I - I

XX xz

I + 21

XX xz

+ 21

13

(9)

where the denominator in the above equations is the total light intensity.

By substituting the elements of the matrix of equation (7) into equations (8)

and (9)

,

we obtain

r =

3cos 4 6 - cos2

6 3cos2

<5 - 1

2cos 2 6 ^ and

6 - 20cos 2

6 + 14cos 4 6

( 10 )

3cos 2

<S - 1

(9 - 14cos2

9 + 5cos 4 0) - (3 - 18cos 20 + 15cos 4 9 ) cos 2 S

(ID

In deriving the above equations we have made the assumption that the

chromophore rotational relaxation time, r r , is much longer than the

fluorescence decay time, r d . This assumption must be checked experimentally.

We note, however, that we are incorporating long rotational relaxation times

into the relaxation behavior of the chromophore by covalently bonding it to the

main chain of polybutadiene. Such an effect has been observed by Monerie and

co-workers who found that, when anthracene was bonded to isoprene, its r

r increased by two orders of magnitude and that r

r » r d

. In general, when the

rotational relaxation is taken into account, the expression for anisotropy is

r = F(cos 2 9 , cos 4 6

)

•

G

(cos 2 8 ) • (r d /r r + 1) _1

, (12)

where F expresses the effect of orientation, G expresses the dependence on the

angle 5, and the last term expresses the effect of the rotational relaxation.

If r

r » r d , then (r d /r r + l)

-1 — 1. Based on the results of Monerie, we will

neglect rotational relaxation effects, however, we intend to verify this

assumption in future experiments.

9
Experimental Procedure

The experimental design consists of using a capillary flow apparatus and a

Weissenberg rheometer to make simultaneous measurements of non-Newtonian

viscosity and fluorescence anisotropy as a function of shear rate. The

capillary flow apparatus, which is diagrammed schematically in Figure 6, has

been incorporated into a commercial fluorimeter. It consists of a glass

reservoir vessel with a capacity of 500 cm3 which sits at the head of a

vertically oriented capillary. The capillary extends through the sample

chamber of the fluorimeter and is connected to a collection vessel at the

bottom end. Capillary diameters of 1 or 2mm are used with a length of

approximately 25 cm. Both are made of borosilicate glass which transmits

excitation light with wavelengths as short as 350 nm. The reservoir at the

head of the capillary is surrounded by a brass pressure vessel which can be

pressurized with nitrogen gas up to 7 x 10 5 Pa (100 psi) . The pressure is

measured using a resistance type pressure transducer. The shear rate

experienced by the liquid in the capillary is varied by changing the pressure

We use the classical equations of capillary flow for a Newtonian fluid:

V =

ttR

4 AP

8Q ' L

(13)

and

4Q (14)

ttR3

where rj is the viscosity, R is the radius of the capillary, AP is the pressure

difference across the ends of the capillary, Q is the flow rate, L is the

length of the capillary, and 7 is the shear rate. Q, the flow rate of material

through the capillary, is obtained by measuring the amount of material eluted

from the capillary in a given time period.

10
A Weissenberg cone and plate rheometer is also being used in this study. This

equipment has been instrumented so that fluorescence anisotropy measurements

can be made simultaneously with the rheological measurements. The apparatus is

depicted in Figure 7. Excitation light energy from an argon ion laser is

directed to the specimen between the cone and plate. The fluorescence spectra

is collected at ninety degrees by an optical fiber which sits below the

optically transparent polymethylmethacrylate plate. In the experiment, the

cone rotates but the plate remains stationary.

In our initial experiments, the capillary apparatus was used to measure

viscosity and fluorescence anisotropy of a low molecular weight polybutadiene

doped with the labelled polybutadiene at a concentration of 10“ 5 molar. The

number average molecular weight of the polybutadiene is 2800 while the number

average molecular weight of the labelled polybutadiene is 12,000. The low

molecular weight of the specimen, 2800, is below the entanglement molecular

weight, 6000, for polybutadiene so that the rheological polymeric effects

should not be observed. This experiment was carried out in order to obtain a

frame of reference for the behavior of a Newtonian material before proceeding

with the non-Newtonian material.

The non-Newtonian polymer which we are studying is also polybutadiene but with

a number average molecular weight of 24,000, i.e., well above the entanglement

value. This specimen was also doped with the labelled polybutadiene at a

concentration of 10~ 5 molar.

11
Results

Figure 8 shows a fluorescence spectrum for the anthracene labelled

polybutadiene as a dopant in the low molecular weight (M^ = 2800)

polybutadiene. This spectrum was obtained for an excitation wave length of 398

nm using the commercial fluorimeter. The anisotropy measurements, calculated

according to equation (1) , were made over a wavelength range from 420 to 470 nm

and for a pressure range from 0 to 50 psi. The viscosity and shear rate were

obtained using equations (13) and (14).

Figure 9 shows viscosity and fluorescence anisotropy as a function of shear

rate for the doped low molecular weight (1^ = 2800) polybutadiene. We note

that this material is Newtonian in its behavior over the range of shear rates

from 20 to 70 s” 1

. The anisotropy, which is also constant, correlates with the

Newtonian behavior. Our interpretation of these data is that, within the

limits of uncertainty of our measurements, molecular orientation is not seen in

the fluorescence anisotropy for Newtonian polymer melts. Since the molecular

weight of this specimen is below the entanglement value, we picture the

molecule tumbling in the velocity field of the capillary, but, on the average,

the molecule remains unextended.

The viscosity and fluorescence anisotropy for the higher molecular weight

polybutadiene, = 24,000, are being measured using the Weissenberg rheometer.

These experiments, which are incomplete at this time, will be the subject of a

future publication.

12
C. Mixing Experiments

Previous Work

In previously reported experiments on mixing, we established the feasibility of

using fluorescence intensity observations to monitor the quality of mix of

7 8

ingredients in a two component material. ’ The components used in the mixing

experiments were a polybutadiene based polymer called PBAN, which was doped

with a fluorophore, coumarin 30, and aluminum oxide particulate material. The

mixing was carried out in a small laboratory mixer with a glass wall to

facilitate light excitation and emission. We observed that the fluorescence

intensity, which was monitored as a function of time at a fixed position in the

mixer, became constant as mixing proceeded. These data are shown in Figure 10.

Our hypothesis is that uniform mixing is achieved when fluorescence intensity

is constant with time. Qualitative support for this hypothesis was obtained

from micrograph observations of the well mixed material in an optical

_

. . . 7,8 transmission microscope.

Fluorescence Microscope Experiments

In order to establish quantitative support for the mixing hypothesis, we have

continued experiments on fluorescence monitoring of mixing using an

epifluorescence microscope to observe fluorescence intensity, optical

transmittance, and near neighbor distances in poor and well mixed materials.

The microscope, optics, and photomultiplier assemblies are products of Carl

9 Zeiss GMBH. The instrumented is fitted with a mercury arc lamp source,

photomultiplier detector, grating monochromators, and a camera. The excitation

wavelength was set at 366 nm (for dimethyl anthracene) and emission was

observed at 429 nm. The precision in the fluorescence intensity measurement

13
was found to be ±1.5% for these experiments.

Near Neighbor Distance Measurements

The specimen materials for these experiments were a low molecular weight

polybutadiene (M^ = 2800) doped with dimethylanthracene (8 x 10" A molar

concentration) -and copper spherical particles whose average radius was

41 ± 8 fim. The copper particles were isolated from a larger batch by passing

them through sieve cloth; this procedure confined their diameters to within

74 /j. m and 125 nm . Two specimens, one poorly mixed and the other well mixed,

were prepared from copper and polybutadiene ingredients which combined to yield

a mixture 83% by weight or 32% by volume copper. Both specimens were placed on

microscope slides, covered with a glass slip, and pressed into a two

dimensional mixture so that all of the copper particles resided in the plane

between the slide and cover slip. In this configuration, the specimen

thickness equals approximately the diameter of the largest copper spheres.

Eight distinct views of each specimen were obtained by randomly moving the

microscope objective from one position to another. At each position, a

photograph was taken and the fluorescence intensity was measured. A typical

photograph of the well mixed specimen is shown in Figure 11. The central

circle on the photograph, whose diameter is 281 /im, defines the region from

which the fluorescence intensity was measured. Near neighbor distances were

measured by isolating the central particle in the region and observing the

distance to the closest six particles for comparison to a hexagonal array and

to the closest four particles for comparison to a face centered square array.

14
The near neighbor distances and fluorescence intensity data for the mixed and

unmixed specimens are presented in Tables I and II, respectively. The

calculated average distances, <dnn >, are for the nearest six particles except

for two views of the unmixed specimen for which too few particles were present.

The unmixed specimen is distinguished from the mixed specimen by larger

fluctuations in fluorescence intensity as expressed in the standard deviations:

Average I f (mixed) = 39.7 ±5.7

Average I f (unmixed) = 39.1 ±17.1.

The overall average of near neighbor distances is:

<dnn > (mixed) = 86.0 ±16 /zm

<dnn > (unmixed) = 121.5 ±37 /zm.

These numbers demonstrate the correlation between fluctuations in I f and

uniformity in near neighbor distance and establishes quantitative support for

the fluorescence/quality of mixing hypothesis. We note that <dnn > for the

mixed specimen is nearly equal to the average diameter of the spheres,

2r = 82 ±16 /zm, and interpret this to mean that the two dimensional specimen is

more closely packed than the volume concentration would indicate (see below)

.

The magnitude of the standard deviation for <dnn >, ±16 /zm, is partially

generated by the distribution in particle size, especially for the case when

the particles are closely packed.

We can analyze the well mixed specimen by considering that the particles are

positioned in two dimensional space in hexagonal or in face centered square

arrays. For the two dimensional hexagonal array whose thickness is the

diameter of the particle, the relationship between the near neighbor distance,

dh , and vc , the volume concentration of particles, is

15
( 15 )

1 47rr2 ~| 1/2

1 573vc J

For r = 41 /im and vc =0.32, we obtain dh = 113 /im which is 31% larger than the

overall average near neighbor distance of 86 /zm. For the face centered square

array, the near neighbor distance, df

, is

Again, using r = 41 /im and vc =0.32, we calculate dfs = 105 /zm which is 32%

greater than the overall average of the closest four near neighbors, 79.6 /zm,

as calculated from the data of Table I. The discrepancy between our

observations and the calculated near neighbor distance from the assumed arrays

originates from the method by which the specimens were prepared. When the

three dimensional specimen is squeezed into two dimensions, particle

impingement and displacement must occur as the specimen is deformed into its

final shape. Also, a lateral displacement of liquid, which can flow passed and

around relatively stationary particles, will result in a smaller near neighbor

distance in two dimensions than that which existed in three dimensions. In

this case, the procedural steps of mounting the specimen on the microscope

slide are viewed as part of the mixing process which yielded the well mixed

specimen which we examined.

Optical Transmittance Measurements

Optical transmittance measurements were made for the purpose of establishing a

correlation with the fluorescence intensity of unmixed and mixed specimens.

The fluorescence microscope, described above, was also used in these

experiments. The experimental procedure consisted of focusing the microscope

on a section of the specimen, measuring the fluorescence intensity at 429 nm

df s (16)

16
(emission for dime thy lanthracene) , and measuring the optical transmission

intensity at 520 nm.

The materials used for these mixtures were the low molecular weight

polybutadiene (M^ = 2800) and aluminum oxide particles with average grain size

of 9.5 /xm. The polybutadiene was doped with dimethylanthracene to a

concentration of 8 x 10' 4 molar. The samples were prepared from a combination

of the two components for which the weight concentration of aluminum oxide was

42% and the volume concentration was 24%. Two specimens were examined, a nonmixed specimen and a well mixed specimen. Each was placed onto a microscope

slide and covered with a glass cover slip. The diameter of the field of view

was 70 /im and the thickness was held constant at 465 fim throughout the

experiment. Fifteen unique views of each specimen were obtained by randomly

moving the microscope objective from one position to another. At each

position, the fluorescence intensity and optical transmission was measured.

The data, shown in Figure 12, display the correlation which exists between the

optical transmittance and the fluorescence intensity. Data from the unmixed

specimen span a wide range of variation in both parameters, whereas the data

from the mixed specimen occupy a confined position on the plot. Since the

optical transmittance is inversely related to the number of particles in the

field of view, these data demonstrate that the fifteen views of the mixed

specimen contained approximately an equal number of aluminum oxide particles in

this microscopic volume, the definition of a well mixed material. The

concurrent uniformity of fluorescence intensity and optical transmittance for

the mixed specimen provides rigorous support for the hypothesis that constant

fluorescence intensity over spatial and/or temporal sampling of a material is

17
evidence that uniform mixing has been achieved.

SUMMARY

The work described here falls into three categories of activity: the synthesis

of a polymeric chromophore; the measurement of fluorescence anisotropy and

molecular orientation; and, the mixing experiments to establish quantitative

support for the fluorescence intensity/quality of mixing hypothesis. We have

achieved significant results in each of these work areas. The polymeric

chromophore has been synthesized by covalently bonding f luorescently active

anthracene to polybutadiene. This new chromophore is presently being used in

experiments to measure molecular orientation and to correlate these

measurements with non-Newtonian viscosity. The equipment and instrumentation

for the fluorescence anisotropy experiments is now in operation. The mixing

experiments involved measurements of near neighbor distances and optical

transmittance on two component mixtures and the correlation of these data with

fluorescence intensity observations. The results of the mixing experiments

give quantitative support to the hypothesis that constant fluorescence

intensity with time indicates that uniform mixing has been achieved.

18
TABLE I

Near Neighbor Distances for the Well Mixed Specimen

Sample dl d2 d3 d4 d5 d6 <dnn>3 S.D. d PMTb

mixed#l 107 90.9 88.6 121 114 94.9 103 13.3 45.19

mixed#2 72.0 85.7 62.3 84.6 85.1 85.1 79.1 9.78 31.53

mixed#3 91.4 77.1 98.9 97.1 74.3 103 90.3 11.9 37.62

mixed#4 73.1 97.1 68.0 68.6 81.1 79.4 77.9 9.9 40.06

mixed#5 68.6 62.9 89.1 60.0 103 103 81.1 19.8 47.89

mixed#6 38.9 86.9 102 71.4 57.1 85.1 73.6 22.8 32.23

mixed#7 103 94.3 79.4 102 103 100 97.0 9.2 41.41

mixed#8 88.6 90.9 74.3 70.9 97.7 91.4 85.6 10.6 41.46

a Distances measured in /j,m.

b PMT (Photomultiplier Tube) readings are in millivolts.

19
TABLE II

Near Neighbor Distances for the Non-Mixed Specimer?

Sample dl d2 d3 d4 d5 d6 «lnn>b S.D. d PMTC

non-mix#l 88.6 88.6 85.7 120 127 117 104 18.8 17.22

non-mix#2 114 94.9 117 40.0 125 35.4 87.7 40.0 18.76

non-mix#3 115 135 120 103 114 106 116 11.4 39.20

non-mix#4 111 121 92.0 135 97.8 137 116 18.8 41.16

non-mix#5 154 103 90.9 131 133 169 130 29.5 26.13

non-mix#6 >234 225 202 >234 >234 >234 >234 - 58.20

non-mix#7 >234 >234 >234 >234 >234 >234 >234 - 60.36

non-mix#8 94.3 187 165 154 148 122 145 32.7 51.70

a Distances designated as >234 indicate that no near neighbor was within the

field of view.

b Distances measured in fim.

c PMT (Photomultiplier Tube) readings are in millivolts.

20
References

1. Principles of Fluorescence Spectroscopy , by J . R. Lakowicz , Plenum Press,

New York , 1983

.

2. Polymer Photophvsics . edited by D. Philips, Chapman and Hall, New York,

1985.

3 . J. H. Nobbs, D. I. Bower, I. M. Ward and D. Patterson, Polymer, 15 . 287

(1974).

4. L. L. Chapoy and D. B. DuPre, in Methods of Experimental Physics . Vol. 16A,

Edited by R. A. Fava, Academic Press, New York, 1980.

5. J. P. Jarry and L. Monnerie, J. Poly. Sci., Poly. Phys . 16., 443 (1978).

6. J. P. Jarry and L. Monnerie, Macromolecules, 12., 927 (1979).

7. A. J. Bur, F. W. Wang, and R. E. Lowry, Proc. Soc. Plastics Eng., Annual

Tech. Meeting, April, 1988.

8. "In Situ Fluorescence Monitoring of the Viscosities of Particle-Filled

Polymers in Flow", by A. J. Bur, F. W. Wang, and R. E. Dehl , NBS Internal

Report NBSIR 88-3694, National Bureau of Standards, Gaithersburg, MD 20899.

9. Identification of a commercial product is made only to facilitate

experimental reproducibility and to adequately describe experimental

procedure. In no case does it imply endorsement by NIST or imply that it is

necessarily the best product for the experimental procedure.

21
'
SYNTHESIS OF POLYMERIC CHROMOPHORE

HOOC-PB-COOH

DCC

DMAP

0

ii C-O-C-PB —COOH

PB - Polybutadiene (My, - 12,000)

NaBH^ - sodium borohydride

DCC - dicyclohexylcarbodiimide

DMAP - dimethylaminopyridine

Figure 1 . The chemical synthesis for labelling carboxyl terminated

polybutadiene with anthracene is shown. It is a two step procedure: first,

convert the 9,10 dicarboxylanthracene to anthracene dimethanol, and second,

covalently bond this with the polybutadiene via an esterification reaction.
INTENSITY

GPC : POLYMERIC CHROMOPHORE

polybutadiene

30.0 40.0 50.0 60.0

ELUTION VOLUME

Figure 2 . A gel permeation chromatograph is shown for the labelled

polybutadiene and for the starting polybutadiene material. The labelled

polybutadiene has a molecular weight approximately two times that of the

starting material.
z

Figure 3 . The laboratory coordinate system with the molecular axis of the

chromophore , M, is shown.
c

M

Figure 4 . The molecular coordinate system with absorption and emission dipoles,

a and e, is shown. a and e are at angles a and 8 with respect to M.
Figure

refers

Source

h/V*

Source

A/V*“

5.. The definitions of r and r' are schematically portrayed,

to the matrix element of equation (7j.

- *13

+ 2i13

I 31

2131

Here, I XJ
CAPILLARY FLOW EXPERIMENT

Measurement: Fluorescence Anisotropy as a Function of Shear Rate

or Applied Pressure.

Figure 6 . A s practice, the

each other.

chematic diagram of the capillary flow apparatus is shown,

excitation and emission light beams are at 90° with respec

In

t to
RHEOMETER OPTICS

polarizer

laser

specimen

analyzer

optical fiber

\

transparent

plate

monochromator and detector

Figure 7 . A schematic diagram of the optically instrumented Weissenberg

rheometer is shown.
in1

1:n

sin

(

I

ho

LI

SO

I

ids

PBQH with taqed Poivbutadiene

410 430 450 470 490 510

WAVENUMBER

Figure 8 . The fluorescence spectrum for the labelled polybutadiene doped in a low molecular weight (M^ = 2S00) polybutadiene is plotted. The excitation

wavelength was 398 nm.
ANISOTROPY

PB (1^ --2800) doped with tagged PB (10‘^ M)

SHEAR RATE (s'

1 )

Figure 9 . Fluorescence anisotropy and viscosity are plotted against shear rate

for the low molecular weight (M^ = 2800) polybutadiene doped with the

anthracene labelled polybutadiene.

VISCOSITY

(Poise)
>

HM

C/5 2

W u

h w

2 C/D M \CO W H

O 2

2 D

W O

0 U

C/5 O

W iJ

ceS M

O X

C5

(X

6.0

PBAN & AI 2O3 (14 pm, 67% wt.)

1

1 1 1 chromophore: coumarin (10"^ M)

auti

2.0

0

mixer on

-L -L 4 6

MINUTES

8 10

>

H

M

CO2

W

W

u2

W

o

in

w

cd

o2

_l

MINUTES

Figure 10 . Fluorescence intensity vs time is plotted for a combination of PBAN

and aluminum oxide particles, 67% by weight aluminum oxide. The PBAN is doped

with the chromophore, coumarin 30. The uniform fluorescence intensity as a function of time indicates that uniform mixing has been achieved.
Figure 1 1

.

A photograph of the two dimensional mixture of polybutadiene and

copper particles is shown. This picture is for the well mixed condition.
PERCENT

TRANSMISSION

FLUORESCENCE MICROSCOPE MEASUREMENTS

100

80 -

60 -

40 -

20 ~

0 L

0

Polybutadiene/A^Og Mixture

*

* non- homogeneous specimen

o homogeneous specimen

* *

* - * ?

* 3S& * *

_] i l i 20 40 60 80 100

RELATIVE FLUORESCENCE

F igure 1

. %Transmission is plotted vs relative fluorescence intensity for

mixed (o) and unmixed (*) specimens of polybutadiene and aluminum oxide, 42%

weight aluminum oxide.
NBS-114A 'REv. 2-80

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publ i cation D ate BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NISTIR 88-3892 NOVEMBER 1988

4. TITLE AND SU BTITLE

IN SITU FLUORESCENCE MONITORING OF THE VISCOSITIES OF PARTICLE-FILLED

POLYMERS IN FLOW

I

5. AUTHOR(S)

A.J. Bur, F.W. Wang, A. Lee, R.E. Lowry, S.C. Roth,

6. PERFORMING ORGANIZATION (If join t or other than NBS, see in struction s)

and T.K. Trout

7. Contract/Grant No.

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS i Street . City. State,

Office of Naval Research, Code 1132-P

Ballston Tower #1

800 N. Quincy Street

Arlington, VA 22217

10. SUPPLEMENTARY NOTES

NOOO 14-8 6-F-O 115

8. Type of Report & Period Coverec

Annual Report

zip ,

Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant in formation. If document includes a significant

bi bl mgraphy or literature survey, mention it here)

Work during FY 88 has focused on three areas: the chemical synthesis of a polymeric chromophore; the design of experiments to measure fluorescence anisotropy

and non-Newtonian viscosity as a function of shear rate; and, measuring the qualityof-mix of a two component material using a fluorescence microscope. Significant

results from these areas of work are: (a) a polymeric chromophore, consisting of

anthracene covalently bonded to polybutadiene, has been synthesized and characterized

by gel permeation chromatography and infrared observations. The number average

molecular weight is 12,000 which is above the entanglement molecular weight for

polybutadiene; (b) experiments using the polymeric chromophore as a dopant in a

Newtonian fluid, very low molecular weight polybutadiene, show that fluorescence

anisotropy correlates with the viscosity, i.e., it remains constant as a function of

shear rate; and (c) using a fluorescence microscope, we have measured optical

transmittance and near neighbor distances between particles in a matrix/particle

mixing experiment and correlated these data with fluorescence intensity fluctuations.

12 .

13.

I

KEf -<‘<ORDS S.x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicaon sj fluorescence anisotropy; fluorescence photobleaching ; fluorescence spectroscopy;

laminar flow; polymer fluorescence labelling; polymer processing; propellant mixing;

propellant processing; velocity; velocity gradient; wall slip

AVAILABI- ty

X ^ n 1 1 1~. i tec = 0 ' Z'~* ciai D i str i dud on . Do No". Re'ease to NTIS

C r oe r -'O'" Superintendent c" Documents, U.S. Government Printing Office, 'Washington,

' 20402 .

14. NO. OF

PRINTED PAGES

36

D.C.

15. Price

X O roer -rom Nationa' Technical Information Service (NTIS), Springfield, VA. 2216 1 $11.95

J S C O MM- D C '43-P 80
'

.