STAND & TECH R.I.C. NAT L INST. OF

A 11 ID 4 0D2533

NATIONAL INSTITUTE OF STANDARDS &

TECHNOLOGY

Research Information Center

Gaithersburg, MD 20898

NBS

Pub!i- A 1 1 1 2 73D172

cations

NBSIR 88-3694

In Situ Fluorescence Monitoring of the

Viscosities of Particle-Filled Polymers in

Flow

Anthony J. Bur, Francis W. Wang, and Ronald E. Dehl

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Gaithersburg, MD 20899

January 1988

Annual Report

Contract No. N00014-86-F-0115

R. S. Miller, Contract Officer

— QC

100 laval Research

. U 56 ncy St.

88-3694 VA 22217

1988

C . 2

NBSIR 88-3694

IN SITU FLUORESCENCE MONITORING OF THE

VISCOSITIES OF PARTICLE-FILLED POLYMERS IN

FLOW

Anthony J. Bur, Francis W. Wang, and Ronald E. Dehl

Research Information Center

National Bureau of Standards

Gaithersburg, Maryland 20899

Ciaoo

l^t sr

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Gaithersburg, MD 20899

January 1988

Annual Report

Contract No. N00014-86-F-0115

R. S. Miller, Contract Officer

Prepared For: Office of Naval Research

800 N. Quincy St.

Arlington, VA 22217

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

During FY87, our activity has focused on the development of measurement

equipment, laboratory experiments using fluorescence monitoring, and the

synthesis of a polymeric fluorescent chromophore . Laboratory equipment

development has consisted of the design and construction of a capillary flow

apparatus and a laboratory mixer. The capillary apparatus has been

incorporated into a commercial fluorometer and is being used for the

simultaneous measurement of fluorescence anisotropy and rheological parameters

of concentrated polymer solutions and low molecular weight polymers. We have

demonstrated the feasibility of the capillary measurement system by observing

the anisotropy of a toluene solution of a polymer binder as a function of

capillary head pressure from 0 to 40 psi. A mixer, which incorporates corotating and counter-rotating shearing elements and glass walls for viewing

fluorescence, has been constructed and used to monitor the mixing of a low

molecular weight polybutadiene based polymer and aluminum oxide. In other

experiments, we have made observations of the dependence of the intensity of

the fluorescence spectra from a doped polymer binder as a function of

temperature at zero shear. In addition, we have used a cone and plate

viscometer (a Weissenberg rheometer) to measure the viscosity of a polymer

binder as a function of filler content (14 /xm aluminum oxide particles) over a range from 0 to 75% by weight. Chemical synthesis of a polymeric chromophore

is in process; it consists of reacting a bifunctional anthracene molecule with

polybutadiene so that the fluorescently active anthracene is positioned at the

center of the polymer chain.

Key Words: fluorescence anisotropy; fluorescence spectroscopy; polymer mixing;

propellants; rheology; zero shear viscosity.
INTRODUCTION

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

obtain both microscopic and macroscopic information. 1 Its application to

propellant processing is a new endeavor which will require significant

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

large body of fluorescence spectra 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 zero shear viscosity, non-Newtonian viscosity, molecular orientation,

intersegmental mixing at the molecular level, and the quality of mixing of

specimen ingredients.

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 non2
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 develop mixing

equipment and equipment which can be used to measure fluorescence spectra and

non-Newtonian viscosity simultaneously, (b) to carry out laboratory experiments

on the fluorescence monitoring of the following: zero shear viscosity of a

polymeric binder, fluorescence anisotropy of a polymer solution in capillary

flow, and the mixing of two component specimens, and (c) to synthesize a

polymeric chromophore which can be used to detect the molecular orientation and

non-Newtonian viscosity in a flowing propellant material. We report on these

efforts below.

EXPERIMENTAL PROCEDURE

MIXING EXPERIMENT

The materials for the mixing experiment consisted of the polymer binder PBAN,

which we obtained from American Synthetic Rubber, 2 aluminum oxide filler

particles which had a nominal grain size of 14 /xm, and the chromophore coumarin

30 which was obtained from Eastman-Kodak. 2

3
According to the supplier's specifications, PBAN is a ter-polymer which is 85%

butadiene, 11% acrylonitrile, and 4% acrylic acid; it has a weight average

molecular weight of 6000. The viscosity of PBAN at 25°C is 369 poise.

The dopant chromophore which we used for the mixing experiment was coumarin 30.

It was chosen because it satisfies the following criteria which we have

established:

o Fluorescence intensity must be independent of the polarity of the

molecular neighborhood of the chromophore;

o The chromophore must be chemically stable and not susceptible to

photobleaching by the excitation photons;

o Excitation and emission must occur at visible wavelengths.

The last criterion is not a necessary condition but one of convenience.

Prior to mixing PBAN with the Al^O^ filler, PBAN was doped with coumarin 30 to

a concentration of 10" 4 molar. To do this, a few milligrams of coumarin were

dissolved in a few drops of a 50/50 ethanol/toluene mixture and then mixed with

PBAN. This mixing was carried out with ease because both materials were in the

liquid state.

Mixing of the doped PBAN and Al^O^ was carried out in a mixer which was

constructed in our laboratory and is shown schematically in Figure 1. The

cylindrical wall of the mixer is a glass tube which is approximately

2.54 cm in diameter by 14 cm in length. The specimen volume in the mixer

is 42 cm3

. There are two sets of mixing blades which can be driven in

co-rotating or counter-rotating modes of motion by the motors shown. One set

of blades rotates at the outer circumference of the mixer near the glass wall.

4
This set is connected to the uni-directional motor and contains a flat brass

piece which functions as a scraper in order to prevent material from

accumulating at the wall. The other set consists of a single twisted brass

piece which is connected to the bi-directional motor and rotates on the

cylindrical axis of the mixer. Both motors rotate at approximately 10 rpm,

i.e. with a period of revolution equal to 6 seconds.

In Figure 2, we show the experimental arrangement for collecting the

fluorescence spectra during the mixing operation. A 458 run excitation light

beam from an argon ion laser was directed through a beam splitter to the glass

wall of the mixer. The diameter of the light beam was approximately 1 mm, and

its penetration into the sample varies with the amount of particle scattering.

The beam splitter is employed in order to detect the back scattered

fluorescence radiation. Fluorescence from the coumarin chromophore was

isolated at one wavelength by setting the monochromator to 500 nm, and the

fluorescence signal was detected by a photo tube and counter, and stored in a

computer. The data sampling time was set at 0.2 seconds so that 30 data points

were obtained for each revolution of the mixer motors.

ZERO SHEAR VISCOSITY EXPERIMENT

The binder which we used in the zero shear viscosity experiment was obtained

from J. Manser of Aerojet General. 3 It is a copolymer of

bis ( az i dome thy 1) oxetane and nitratomethylmethyloxetane and is designated as

BAMO/NMMO. 4 The molecular weight was reported to be 18, 000. 3 It was doped

with the chromophore, p-dimethylaminobenzylidene malononitrile (DMABMN) , to a

5
concentration of approximately 10" 4 molar by combining chromophore and polymer

in solution using methylene chloride as the common solvent. The solvent was

evaporated by maintaining the temperature of the specimen above the boiling

point of methylene chloride (40° C) for 24 hours.

The DMABMN chromophore was chosen for this experiment because it is known that

its fluorescence intensity is dependent on the viscosity of the host material. 5

Fluorescence spectra from 450 to 650 nm were obtained as a function of

temperature from this specimen using a commercial fluorimeter which had a

temperature control jacket in the specimen chamber. The excitation wavelength

was 440 nm.

FLUORESCENCE ANISOTROPY

The capillary flow apparatus will be used to study the flow of concentrated

polymer solutions and low molecular weight polymers by observing the

fluorescence anisotropy of polymer molecules during flow as a function of shear

rate. This apparatus has been incorporated into a commercial fluorometer as

depicted in the schematic diagram of Figure 3. The apparatus consists of a

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

vertically oriented capillary. The capillary extends through the sample

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

bottom end. It is made of pyrex glass, has a capillary diameter of 1 mm, and is

25 cm long. Conversion to other capillary diameters is easily achieved. The

reservoir at the head of the capillary is surrounded by a brass pressure vessel

6
which can be pressurized by nitrogen gas to 100 psi. Pressure is monitored by

a resistance type pressure transducer. The shear rate of the liquid in flow is

controlled by adjusting the pressure.

Although the PBAN molecule should not be f luorescently active and toluene does

not display fluorescence in the wavelength range of our investigation, we

observed fluorescence spectra over the range 350 to 450 nm for excitation at

325 nm. We attribute this fluorescence to an additive or an impurity in the

polymer sample. The fluorescent chromophore is not necessarily chemically

bound to the polymer molecule, but we have taken advantage of its fortuitous

presence to test our experimental technique.

The measured quantity in this experiment is fluorescence anisotropy, r. It is -

defined as

r ^vv “ ^vh

ivv + 2Ivh

( 1 )

where Ivv refers to vertically oriented excitation and emission polarizers and

Ivh refers to a vertically oriented excitation polarizer and horizontally

oriented emission polarizer. The measured intensities are appropriately

corrected for differences in detection sensitivity for vertically and

horizontally polarized light.

VISCOSITY MEASUREMENTS

A Weissenberg rheometer has been used to make measurements of the viscosity of

PBAN filled with 14 jj.m grain size aluminum oxide. The measurements were

7
carried out at room temperature for filler content over a range of 0 to 75% by

weight. This instrument is being fitted with optical fibers which will be

placed at the cone and plate assembly in order to obtain fluorescence

anisotropy and viscosity measurements simultaneously.

SYNTHESIS OF A POLYMERIC CHROMOPHORE

For the measurement of molecular orientation and non-Newtonian viscosity, a

polymeric chromophore , i.e. a molecule which is long enough to orient under the

influence of processing shear stresses, will be used. We are in the process of

reacting a bifunctional anthracene molecule with polybutadiene so that the

fluorescently active anthracence is positioned at the center of the polymer

chain. The results of these efforts will be the subject of future reports.

RESULTS AND DISCUSSION

MIXING EXPERIMENT

To prepare the specimen for mixing, aluminum oxide filler material (14 nm grain

size) and PBAN were added separately to the mixer without any premixing at 58%

filler by weight. Prior to turning the mixer on, the excitation light beam

from the laser was directed at the chromophore -rich PBAN which produced a

strong fluorescence signal, 200 kilocounts/s , as shown in Figure 4. At 150

seconds, the mixer was turn on and was operated in the counter-rotating mode.

At the start of mixing, large variations in intensity were observed. The

intensity variations are seen as periodic spikes in the data with a period of

8
six seconds. These spikes occur every revolution of the mixer as the blades

bring chromophore - rich and -poor regions of the specimen into the sampling

volume of the mixer. In addition to the spikes, an overall decrease in

fluorescence intensity occurred within the first 30 seconds of mixing. This

decrease in the intensity is attributed to two causes: one, the coumarin

chromophore in the sampling volume is displaced by the A^O^ an<^ two,

light scattering from the 14 filler particles occurs.

In Figure 5, we plot fluorescence intensity data taken after the mixer had been

on for 60 minutes. At this time, the mixer operation is one of alternating

from counter-rotating to co-rotating blade motion every 2 minutes. The

alternating pattern is seen in the data and reflects the change from counterrotation to co-rotation and' vice versa every minute. It is seen that the

intensity spikes which occur every 6 seconds are an order of magnitude less

than that seen in Figure 4, an indication that the distribution of chromophores

throughout the specimen is approaching uniformity.

At this point in the mixing experiment, the mixer was opened and more aluminum

oxide was added in order to fill the mixer to maximum. This mixture contained

67% Al^O^ by weight. Figure 6 shows the fluorescence intensity data obtained

after the additional filler was added. After nine minutes of mixing, there

remains intensity spiking of approximately 1 kilocount/s, but, after 100

minutes, the intensity is constant to within the sensitivity of our

measurement. Our hypothesis is that uniform mixing has been achieved when

constant fluorescence intensity as a function of time is observed.

9
As a qualitative test of this hypothesis, we used transmission optical

microscopy to examine a 100 /j. m thick smear of the mixture on a glass microscope

slide. Figure 7 is a picture of this observation. The dark areas are filler

particles in the plane of focus. The grey translucent areas contain filler

particles within the thickness of the smear but not in the plane of focus . The

bright regions contain PBAN only and are not overlaid by aluminum oxide

particles so that light is transmitted directly through the specimen. In

assessing the qualitative features of this picture, we note that 67% aluminum

oxide by weight corresponds to 34% by volume.

A rigorous test of our fluorescence/mixing hypothesis will require a

quantitative measure of the spatial, distribution of filler particles in the

polymer binder and a comparison of such observations with an accepted model or

definition of a "good" mixture. This will be the subject of future work.

ZERO SHEAR VISCOSITY

Figure 8 is a plot of fluorescence spectra taken at 25, 60, and 95° C for

BAMO/NMMO doped with DMABMN. The decrease in intensity with increasing

temperature is attributed to the decrease in viscosity of the polymer as

temperature increases

The sensitivity of the fluorescence intensity of DMABMN to the viscosity of the

host material has been studied in detail by Loutfy. 5 DMABMN belongs to a class

of chromophores whose quantum yield of fluorescence is dependent on the

relative magnitude of the intrinsic radiative lifetime of the excited state

10
versus the internal rotational relaxation time, r of the chromophore in its r »

viscous neighborhood. Loutfy found that a clear correlation exists between

fluorescence intensity of DMABMN and the ratio of viscosity to temperature for

the solvents ethylacetate , dimethylphthalate , and glycerol. 5 The correlation

was of the form I a (rj/T) x where x = 1.0, 0.43 and 0.69 for the three solvents

respectively over the temperature range from 0 to 90° C. The functional form of

the correlation, rj/T, is predicted for r

r front the Debye-Einstein-Stokes model

of a sphere or ellipsoid rotating in a viscous medium. The data of Loutfy

demonstrate that viscosity is the dominant influence on the fluorescence

intensity of DMABMN in each solvent, but the molecular hydrodynamics which

determine the internal rotational relaxation time are different in each case. 5

Since we have not measured viscosity of BAMO/NMMO, we do not know the precise

correlation between fluorescence intensity and viscosity. However, Loutfy'

s

work supports our interpretation that the decrease in fluorescence intensity

correlates with a decrease in the viscosity of BAMO/NMMO.

FLUORESCENCE ANISOTROPY MEASUREMENTS

Using the capillary flow apparatus, fluorescence anisotropy of an undoped

toluene solution of PBAN was measured over a wavelength range from 350 to

450 nm as a function of the applied pressure from 0 to 40 psi. The solutions

were 1/3 polymer and 2/3 toluene by volume. Under quiescent conditions, we

observed that the anisotropy, r, was zero. The effect of increasing pressure

or shear rate is shown in Figure 9; we note that the anisotropy is

approximately zero for 10 psi. But, for 20 psi head pressure, r is 0.5 over

the entire scan, indicating that there is significant orientation of the

11
fluorescent transition dipole as the shear rate increases. At 30 and 40 psi

the anisotropy was observed to decrease to zero; we attributed this to the

onset of turbulence at these higher shear rates for which the flow can be

characterized by Reynolds numbers greater than 2,100.

In order to calculate the polymer molecular orientation from anisotropy

measurements, it will be necessary to use a labelled polymer and to have

detailed knowledge of the chromophore position in the polymer chain and its

fluorescence spectra. Such information is not available regarding the data of

Figure 9, but these experiments have served a useful purpose in establishing

the experimental approach and technique. Our future plans for this experiment

and for experiments using the Weissenberg rheometer will include the use of the

polymeric anthracene/polybutadiene chromophore as a dopant material.

VISCOSITY MEASUREMENTS

The viscosity measurements on PBAN filled with aluminum oxide are shown in

Figure 10. These data were taken at room temperature using the Weissenberg

rheometer and are reported for a shear rate of 0.55 s' 1

. Within experimetal

error, and at concentrations below 50% by weight (21% by volume), the viscosity

is a linear function of Al^O^ weight or volume fraction. Above 50% weight

fraction, a dramatic upswing in the viscosity occurs between 65% and 75% weight

fraction (33% and 43% volume fraction).

In the linear regime of the viscosity vs concentration plot, concentrations

below 50% by weight or 21% by volume, the behavior is viewed as being dominated

12
by hydrodynamic interaction between the Al

? 0^ particles. At very dilute

concentrations, we can apply the Einstein equation for the viscosity of a

solution of hard spheres which states that viscosity is a linear function of

the volume fraction of spheres. 6 For concentrated solutions of spheres, other

hydrodynamic models have been developed and take into account higher order

terms neglected in the Einstein treatment. 7 For these models, deviations from

linearity of approximately 5% are predicted at volume concentrations of 20%, in

agreement with our experimental observation. The slope of our experimental

curve, however, is larger by a factor of two than that obtained from the

models. 7 We note that the models do not take into account non -hydro dynamic

interactions such as non- spherical particle shape, collisions, electrostatic

interactions , and aggregations

.

We interpret the departure from linearity in the vicinity of 50% weight

fraction (21% volume fraction) to be caused by the onset of highly cooperative

particle motion which involves both hydrodynamic and non-hydro dynamic effects.

Below 50% weight fraction, the particles rotate or translate in the polymer

matrix as single particles. Above 50%, particle motion becomes highly

cooperative so that the motion of one requires the displacement of many others

.

The transition from linear behavior at low concentrations to the high slope

regime at high concentrations of Al^O^ occurs at a volume fraction for which

spatial packing becomes a factor. We consider the packing of spheres at a

volume fraction of 23% and assume that the spheres have a radius of 7 pm. If

we place the spheres on an hexagonal lattice, then their center- to-center

distance is 28 ^ra, i.e. the edge-to-edge distance between near neighbor

13
spheres, 14 /xm, is equal to the diameter of the spheres. Thus, 23% volume

concentration is the threshold at which particle - to -particle impingement occurs

during translational motion. As the volume fraction of spheres increases above

23%, the translation of a sphere in the hexagonal lattice will require an

increasing amount of cooperative motion with other spheres.

SUMMARY AND CONCLUSIONS

We have described our activities regarding the use of fluorescence spectroscopy

to monitor propellant processing parameters. From the mixing experiments, we

have observed a constant fluorescence intensity at long mixing times which we

associated with uniform mixing of PBAN binder and the aluminum oxide

particulate. A zero shear viscosity experiment was carried out for which

BAMO/NMMO copolymer binder was doped with a viscosity sensitive probe and its

fluorescence intensity was observed as a function of temperature. The decrease

in fluorescence intensity with increasing temperature was associated with the

decrease in the viscosity of the BAMO/NMMO. Experiments for the measurement of

fluorescence anisotropy have been developed. These include a capillary flow

apparatus and a Weissenberg rheometer which is being fitted with optical

fibers. While several experiments have been done with these pieces of

equipment, the measurement of fluorescence anisotropies and their relationship

to molecular orientation and non-Newtonian viscosity await the synthesis of a

fluorescent polymer. Viscosity measurements on PBAN filled with 14 /urn aluminum

oxide particles were made over a concentration range from 0 to 75% by weight.

The viscosity vs concentration data was linear at low concentrations, but

displayed a departure from linearity at approximately 50% by weight which we

14
attributed to the onset of particle cooperative motion involving nonhydrodynamic forces.

REFERENCES

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

York, NY, 1983.

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

experimental reproducibility and does not imply endorsement by NBS

.

3. J. Manser, Aerojet Solid Propulsion Co., Sacramento, CA.

4. J. Manser, R. W. Fletcher and M. R. Knight, High Energy Binders Final

Report . Contract no. N00014-82-C-0800 , Morton Thiokol, Inc., Brigham City,

Utah 84302, August, 1985.

5. R. 0. Loutfy and B. A. Arnold, J. Phys . Chem. 86, 4205, (1982).

6. A. Einstein, Investigations on the Theory of Brownian Movement . Dover

Publications, New York, NY, 1952.

7. J. Happel and H. Brenner, Low Reynolds Number Hydrodynamics . Martinus

Nijhoff Publishers, Boston, MA, 1983.

15
teflon plugs

mixing blades glass tubing

Figure 1 . A diagram of the mixer is shown. The twisted blade, which rotates on

the central axis of the mixer, is driven by the bi-directional motor. Three

blades, driven by the uni -directional motor, are at the outer circumference of

the mixer, near the glass wall; one of these is a scraper which prevents

accumulation of material at the wall.
MIXING EXPERIMENT

mixer

Figure 2 . The optical arrangement for the fluorescence mixing experiment is

shown. By using a beam splitter, the back scattered fluorescence is measured.
CAPILLARY FLOW EXPERIMENT

Measurement: Fluorescence Anisotropy as a Function of Shear Rate

or Applied Pressure.

Figure 3 . A diagram of the capillary flow apparatus is shown. In practice, the

excitation and emission light beams are at an angle of 90° with respect to each

other
FLUORESCENCE

INTENSITY

KILOCOUNTS/SEC

PBAN & Al 2 03 (14 urn, 58% wt.)

4S0.se

3SS.SS

2se.se

ise.se

0.30

S 130 230 300 480 330 630

SECONDS

mixer on. chromophore

:

coumarin (10“^ M)

Figure 4 . Fluorescence intensity versus time is plotted for mixing of coumarin

30 doped PBAN with 58% aluminum oxide by weight. Grain size of the aluminum

oxide was 14 /xm.
PBAN & A1 2 0 3 (14 nm, 58% wt.)

H

CO2

W O

H W

2 oo W

o2

W

o

COW

CAO

2

fe

COH2

2

OO

o

hJM

101 200 300

SECONDS

400 500 000

Figure 5 . Fluorescence intensity versus time is plotted for mixing of coumarin

30 doped PBAN with 58% aluminum oxide by weight. This is the same specimen as was used for the data in Figure 4. The observations are for mixing times

starting at 60 and ending at 70 minutes.
PBAN & AI 2 O 3 (14 pm, 67% wt.)

MINUTES

Figure 6 . Fluorescence intensity versus time is plotted for mixing of PBAN with

67% aluminum oxide by weight. The starting specimen was that used for the data

of Figures 4 and 5 to which more aluminum oxide was added. The plot for 0 to

10 minutes shows the intensity variations at the beginning of mixing. The plot

from 100 to 110 minutes shows the intensity at the end of mixing.
1 100 fj.

Figure 7 . The specimen of Figure 6, having been mixed for 110 minutes, is shown

in a micrograph of a 100 /im thick smear on a microscope slide. The picture was

taken in transmission.
FLUORESCENCE

INTENSITY

COUNTS/SEC

BAMO/NMMO doped with chromophore (10~^ M)

WAVELENGTH nm

Figure 8 . The fluorescence spectra of a doped polymer binder, BAMO/NMMO, are

shown for 25, 60, and 95° C. The chromophore was p-dimethylaminobenzylidene

malononitrile

.
ANISOTROPY PBAN/0CH3 P=10 PSI

ANISOTROPY PBAN/0CH3 P=20 PSI

Wave 1 eng + h ( nm

)

Figure 9. The fluorescence anisotropy for a concentrated solution of PBAN in

toluene is shown for a wavelength scan of 350 to 450 nm for 10 and 20 psi

capillary head pressures.
VISCOSITY

VOLUME FRACTION

Figure 10 . Viscosity vs concentration for aluminum oxide filled PBAN is shown.

The measurements are reported for a shear rate of 0.55 s' 1

.
U.S. DEPT. OP COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 88-3694

2. Performing Organ. Report No. 3. Publication Date

JANUARY 1988

4. TITLE AND SUBTITLE

n In Situ Fluorescence Monitoring of the Viscosities of Particle-Filled

Polymers in Flow"

5. AUTHOR(S)

Anthony J. Bur, Francis W. Wang, and Ronald E. Dehl

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

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

NQ0014-86-F-0115

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

accj ... C Mmrol Pacoareh

8. Type of Report & Period Covered

Annual Report

10/1/86 - 9/30/87

Office of Naval Research

800 N. Quincy Street

Arlington, VA 22217

10.

SUPPLEMENTARY NOTES

2 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 si gnifi cant

bi hi iography or literature survey, mention it here)

During FY 87, our activity has focused on the development of measurement equipment,

laboratory experiments using fluorescence monitoring, and the synthesis of a polymeric

fluorescent chromophore. Laboratory equipment development has consisted of the design and construction of a capillary flow apparatus and a laboratory mixer. The capillary apparatus has been incorporated into a commercial fluorometer and is being used

for the simultaneous measurement of fluorescence anisotropy and rheological parameters

of concentrated polymer solutions and low molecular weight polymers. A mixer which

incorporates co-rotating and counter-rotating shearing elements and glass walls o viewing fluorescence, has been constructed and used to monitor the

r° experiments

molecular weight polybutadiene based polymer and aluminum oXade. In other expera

we have made observations of the dependence of the intensity of the fluorescen

spectra from a doped polymer binder as a function of temperature at aero shear and

we have used a cone and plate viscometer (a Weissenberg rheometer) to measure the

viscosity of a polymer binder as a function of filler content.

12.

KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semicolon s) fluorescence anisotropy; fluorescence spectroscopy; polymer mixing;

propellants; rheology; zero shear viscosity

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