NBS

PUBLICATIONS A11107 3^1054

NBSIR 84-2914

Sizing of Polystyrene Spheres

Produced in Microgravity

George Mulholland

Gary Hembree

Arie Hartman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Manufacturing Engineering

Gaithersburg, MD 20899

July 1985

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84 - 29 1 ^4 1985

RTMENT OF COMMERCE

JREAU OF STANDARDS

c. 2

NATIONAL BUREAU

OF STANDARDS

'~~.T.~Y

NBSIR 84-2914

SIZING OF POLYSTYRENE SPHERES

PRODUCED IN MICROGAVITY

George Mulholland

Gary Hembree

Arie Hartman

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Manufacturing Engineering

Gaithersburg, MD 20899

July 1985

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

Abstr ac

The standard deviation of the size distribution was

determined -For a polystyrene latex produced in a space shuttle

experiment and in an earth-bound control experiment. Values

determined -from direct measurement of transmission electron

micrographs, corrected for magni f i cat i on distortion, were 0.033

um for the space grown material and 0,15 jum for the control. The

standard deviations obtained from an aerodynamic particle-sizer

were only slightly greater than those obtained by TEM? 0,042 um

and 0.20 um for the shuttle and ground material respectively.

However, these values were produced in a few hours versus the

several weeks it took for the electron microscopy. Both of the

techniques used here resulted in measured standard deviations

significantly smaller than those previously reported for this

material .

Keywords: aerodynamic particle sizing? particle counting?

particle sizing? polystyrene latex? optical array

sizing; size distribution? size resolution?

transmission electron microscopy
.

.

'
Table of Contents

Page

1. Introduction . . . = . . . * - . - - 1

2. Transmission Electron Microscopy ........ 2

3. Aerodynamic Particle Sizer ........... 9

4. Average Particle Size and Analysis of

ff-Size Spheres 12

5. Comparison with the Lehigh Results ....... 15

6. Conclusion 17

References 20

List of Tables

Page

Table 1. Size Distribution Parameters ....... 6

Table 2. Number of Off—Size Particles ....... 14

Table 3. Comparison with Lehigh Results ...... 16

List of Figures

Page

Figure 1. Effect of Magnif ication Distortion Caused

by TEN Imaging of Two Identical Spheres

On— and Off-Axis 4

Figure 2. TEN Micrographs of 5.0 jim Polystyrene

Spheres Grown in Space and on the Ground 7

Figure 3. Size Distribution of 5.0 um Polystyrene

Spheres Grown in Space and on the Ground 11

Figure 4. 2—D Hexagonal Arrays of 5.0 ,um Poly—

styrene Spheres Grown in Space and on the

Ground 13

Figure 5. APS Size Distribution of PSL Spheres

Produced by Dvno (distributed by Dow) . . 19

1 . Introducti on

The major effort of this investigation was to accurately

determine the standard deviation, c , of the central peak of the

size distribution for polystyrene (PSD spheres produced in a

space shuttle experiment as well as in an earth bound control

experiment. The space shuttle particles were prepared in an

automated reactor apparatus on the third orbital mission of the

"Columbia" begun on March 22, 1932. The analyzed particles were

nominally 5 Mm in diameter and were produced using a 2.5 um seed

latex and a 10:1 monomer—pol ynter ratio. We found, as did

Vanderhoff et al_ Cl 3, that the size distribution of the space

shuttle spheres was narrower than that of the ground

experiment's. In fact, we found that ff of the central peak of

the space shuttle spheres to be about half the value obtained by

Vanderhoff et a 1_ . So the space grown spheres are in a sense

twice as good as was previously thought. This result was

obtained by two independent techniques, transmission electron

microscopy and aerodynamic particle sizing. The second technique

i s of special interest because it allows the sizing of several

thousand particles in minutes compared to several weeks using

electron microscopy.

In addition to the measurement of the standard deviation, we

determined the average particle diameter and the fraction of of -

size particles for each specimen. The average diameter was

measured by array sizing using a magnification calibrated op*

microscope. Electrical sensing zone instrumentation and opt:._

microscopy were used to estimate the percentage of parti : 1 - s outside- the main peak of the size distribution.

1
In the -following report we present our results -for the

standard deviation, tr , a-? the size distribution the number

1 N

average diameter, D , <D = — S D . ) , and the -fraction at of f -

• n n N . , 1• i=l

size particles. We find that the number average diameter, , n for the space shuttle spheres is 0.24 ym smaller than the ground

based spheres. This finding disagrees with the result of

Vanderhof f et al., who found the space shuttle spheres to be

larger than the ground spheres.

2, Transmission Electron Microscopy

The sample was prepared for electron microscopy by

evaporating a small drop of a diluted suspension of the spheres

on a standard TEM grid. Three grids were prepared from each PSL

specimen. The grids were coated with approximately 20 nm of

carbon and then examined with a JEOL 200 CX

1 at an accelerating

potential of 100 kV and at a nominal 1500X magnification. The

magnification was carefully monitored for variation, but its

absolute value was not accurately determined. About 15

micrographs were taken of each grid in order to obtain 300

particle images to size from each grid. The particle size was

measured directly from the negative using a 7X magnifier with an

accurate millimeter scale reticle. A series of concentric

circles on the reticle enabled quick location of the diameter.

Materials and instruments are identified in this paper in order

to adequately specify the experimental procedure. In no case

does such identification imply recommendation or endorsement by

the National Bureau of Standards, nor does it imply that the

material or instrumentation is the best available for the

purpose.
The value of <x determined from the individual diameter

measurements of 300 particles will differ from the actual

standard deviation of the particle size distribution due to

systematic and random uncertainties in the measurement process*

The systematic uncertainties are caused by the imprecision of the

individual particle measurements and the inclusion of off-size

particles in the central peak of the size distribution. The

former can be further divided into the uncertainty in measurement

of the particle image and the variation of the image size due to

its position in the electron microscope’s field of view

(magnification distortion). The random uncertainty is due to the

size of the measurement sample. We balanced measurement time

with an acceptable accuracy level of ±10% by choosing to measure

300 particles. Each of the preceding error sources and the means

by which we limited them will now be discussed in more detail in

the following paragraphs.

We estimate the uncertainty in the measured diameter. U . 0 ' associated with the use of the graduated magnifier to be 0.022 mm

(corresponding to 0.016 ym) . This uncertainty was determined by

repeat measurements on one particle by one person and by

measurements of the same set of spheres by two persons.

The magnification distortion was determined by taking

micrographs of the same cluster of spheres as they were

positioned in various regions of the field of view. This is

illustrated in figure 1. The magni f i cat i on increased by 4.1% for

particle diameters measured in the radial direction from the

center of the micrograph out toward the corners, at 1500X nominal

The distortion was si gni f i cant 1 y less in the

T

magni f 1 cat i on

.
Composite print showing the same spheres at two different locations in the field of view. The diagram shows magnification

distortion for sphere 2.

Same Sphere On-axis

TEM Magnification Distortion at

3.5 cm off-axis in the Fiim Plane:

~4.0% Radial

~1.4% Tangential

Fig. 1

Effect of Magnification Distortion Caused by TEM imaging of

Two Identical Spheres On- and Off-Axis
tangential direction; + 1 . 4!/:. Consequently all measurements were

made in this direction. The distortion was -fairly constant -for a

-fixed radius about the center of the micrograph. We made use o-f this property by locating the position o-f each sphere within one

of four concentric zones. The diameter of each particle was then

corrected for the average magnification distortion in each zone.

It is important to have a systematic procedure for excluding

off-size particles when calculating the standard deviation, <j , of

the size ditribution. We used a discordancy test [21 based on

the sample kurtosis as the test statistic.

If the sample kurtosis exceeds a value of about 3.40 for a 300

sphere sample, then one or more spheres are off -size at the 57.

level of discordancy. The spheres with diameters farthest from

the average size would be eliminated consecutively until the

sample kurtosis reaches the appropriate value. We typically

found about 15 off-size particles out of a population of

approx i matel y 300. Slightly larger numbers of off—size particles

were obtained for the spheres produced in space in two samples.

The size di str i but i ons of three grids prepared from the

space shuttle spheres and three from the ground spheres were do' • -

The results are summarized in table 1. The a for the space

N

sample kurtosis - — < 1 )

5
shuttle specimen was about 0.033 jam, while that for the ground

specimen was four to -five times larger at 0.151 jam. This large

difference is not apparent -from a visual inspection o-f the

micrographs, as indicated by figure 2.

We were able to test the significance o-f the magni -f i cat i on

distortion correction by repeating the statistical analysis

without the correction for <r -for the same particles. We -find

that it is 9 to 21% greater than the correspondi ng value given in

table 1; the percentage difference increases with an increasing

fraction of the spheres in the outer zones. That our simpl e z on

method has not accounted for al 1 of the distortion 13 i n ci i c ated

Table 1. Size Distr i but i on Parameters

Measurement

Techni ques Sampl

e

a

D (um)

n

a

- (um) ff/D (%) n N

n ( %

)

N

Transmi ssi on SI 5.033 0.036C

0. 72 289 / a U

El ectron S2 5 . 033 0. 034 0.67 293 6. 3

Mi croscopy 34 4.999 0 . 028 0. 59 302 3.6

G

1

5. 188 0. 158 3. 04 302 4 . 6

G2 5. 176 0. 149 2. 88 ji. _* .J _ / G3 5. ISO 0. 146 2. S2 286 5. 4

Aer odynami

c

S2 5. 340 0. 043 0.81 3594 10.5

Particle Sizer S3 5.327 0. 042 0.80 3705

G9 crU m cm 0 . 205 3. 69 4100 6.9

G7 cr c /lir

uj „ j4u 0. 197 3. 56 8143

Optical Array s 5. 04d

Si z i ng G 5.27

a S denotes space shuttle sample and G denotes ground sample,

b n is the number of of f -si ze particles in the size range 4-6 jam

outside the central peak.

c The estimated uncertainty in & for the TEM measurements is

given by a ±10% random component and a systematic component

equal to —0.006 jam. See discussion on page 8.

d The uncertainty in D , including random and systematic errors,

is ±0.12 jam for the shuttle spheres and ±0.18 Mm for the

ground spheres.

6
Fig. 2

TEM Micrographs of 5.0 fim Polystyrene Spheres Grown in

Space (A), and on the Ground (8).

7
by the value of er for sample S4 (28% of spheres in outer zones),

0.028 y m, being smaller than that of the other samples (about 50%

of spheres in outer zones), 0.034 ym and 0.036 ym. Therefore, we

estimate that the component of uncertainty in tr resulting from

residual magnif ication distortion, Li , to be about 0.01 ym for

m

'

the case of 50% of the particles in the outer zones. The

measured standard deviation of the size distribution, ff , is

m broadened from the true <r by the uncertainty in the diameter

measurements, . For statistically independent quantities the

variances add; so we obtain

%=('V) !/2

The quantity U^. itself results from the

determination uncertainty (U =0.016 ym)

e

magnification distortion (U =0.010 ym)

.

m these quantities.

combination of the edge

and the residual

Summing the variances of

U = (u

2

+u

2

)

1

I \ e m / /2

(3)

we obtain Uj equals 0.019 ym. Substituting for in eq. (2) and

setting a ^ equal to the value obtained for sample S2 (0.034 ym)

,

we find tr equals 0.028 ym. In addition to this systematic

uncertainty in u there is also a statistical uncertainty

resulting from the small number of particles measured on each

n n grid. The quantity has a X"

- distribution and at the 95%

confidence level the uncertainty in cr is about ±10% for 300

measurements C3D. Finally, we combine the random and systematic

uncertainties in c by adding 10% to a and subtracting 10% from

m

8
a. This yields -for the case z =0.034 the limits^

m

0.025 ym<<r<0. 037 ym. This is a first-order error analysis in

which the various quantities are assumed to be stati sti cal 1

y

independent. It represents a first step in a detailed error

anal ysi s.

3. Aerodynamic Particle Sizer

The sample preparation is completely different for the

Aerodynamic Particle Sizer (APS) C 4 3 compared to the electron

microscope, because the particles must be dispersed in air for

the APS instrument. A pneumatic nebulizer filled

with a suspension of PSL spheres in water was used to generate

water droplets, some of which contained a PSL sphere. The water

evaporated in seconds leaving the PSL spheres in aerosol form.

By directing the aerosol spray -vertically upward in a cylindrical

tube (7 cm diameter, 30 cm high, closed at the top), we produced

a suitable concentrat i on for the APS, the inlet of which

protruded through the open base of the cylinder. A clean air

flow of about 20 1/min. was introduced in the same direction as

the aerosol flow to insure that the water would evaporate.

The PSL spheres sampled by the APS flow through an

accelerating nozzle. The speed of the spheres is measured at the

exit of the accelerating nozzle with a two—spot 1 aser

vel oci meter . The spheres will lag behind the air according to

their aerodynamic size, and the measured velocity will be

inversely related to the aerodynamic diameter of the sphere,

number—average diameter for the spheres determined by the APS i found to be about 67. larger than the value obtained by electron

9
microscopy or by optical array sizing (discussed below). The APS

is calibrated using liquid droplets of known size. A possible

cause for the 6% discrepancy is the flattening of the liquid

drops in the accelerating nozzle, which would cause them to be

accelerated like a smaller spherical particle.

The standard deviation for the size distribution, as

obtained by the APS, (0.042 Mm) is slightly larger than the value

obtained by electron microscopy (0,033 Mm) . The instrumental

uncertainty is not known for the APS, although we obtained an

instrument standard deviation equal to 0.032 Mm for a 6.0 Mm

liquid aerosol generated by the Bergiund Liu Vibrating Orifice

Aerosol Generator, so the instrument <s is certainly less than

this. It is surprising that the instrument uncertainty is so

small, since one would expect some broadening depending on the

initial position of the droplet in the accelerating nozzle.

The reduced number size di str i but i on , AN/AD, for the space

shuttle spheres and the ground spheres is plotted in figure 3 tor

both the TEM and APS results. The APS size scale has been

shifted so that the number average diameter is close to the TEM

result. The reduced size distribution in figure 3 must be

divided by a scale factor of 0.026 Mm to obtain 1/N AN/AD in

units of Mm *. The space-shuttle size distribution is seen to

have a narrow peak. The rather spiky appearance of the TEM size

distribution is a result of the relatively large statistical

uncertainty resulting from the small number of particles in each

channel. The population of each channel is typically ten times

greater for the APS.

10
(paonpay) ay/NV NOlinsidlSIQ 3ZIS

Fig.

3

Size

Distribution

of

5.0

Polystyrene

Spheres

Grown

in

Space

and

on

the

Ground.
The character! zat i on of the size distribution by an average

particle size and standard deviation is not adequate for the

ground sample because of the complex structure in this histogram.

The broad shoulder, which actually has one or two minor peaks,

may provide a clue to the difference in the growth of the ground

and space shuttle spheres. Also, one can detect a low amplitude

shoulder of the main peak in the small particle region. This is

more apparent in the APS results, although a suggestion of this

structure is also seen in all three of the TEM ground samples.

4 = Average Particle Size and Analysis of Off—Size Spheres

Our most accurate measurement of the number—average sphere

size is based on optical array-si z i ng . By smearing a drop of the

PSL suspension over a microscope slide, one obtains a thin film

of liquid which rapidly dries, leaving regions of hexagonally—

close—packed 2-dimensional arrays. The regularity of the arrays

depends in part on the monodi spersi ty of the spheres. As seen in

figure 4, the array made from the space shuttle spheres is

clearly more regular than that made from the ground spheres.

To determine the number-average sphere size, the center—to—

center distance for a row of particles is measured from a micrograph. While the edge of the particle cannot be accurately

defined by optical microscopy, the position of its center can be

determined to an accuracy cf about 0.05 ,um. The average diameter

is then simply determined by dividing the length of the row by

one less than the number of spheres in the row. The subtraction

of one results from using the cen t er-to—cen ter row length rather

than edge—to—edge row length. A grand average is obtained by

analyzing several different rows. As indicated in table 1 the

12
(B)

Ground Run

Material

Fig. 4

2-D Hexagonal Arrays of 5.0 ium Polystyrene Spheres, Grown in

Space (A) and on the Ground (B).

13
space shuttle spheres have a number average diameter o-f 5.04 Mm

and the ground spheres, 5.2S Mm. A careful error estimate for

this technique has been made including magnif ication distortion,

which is much smaller for optical microscopes than for electron

microscopes, and the systematic error caused by small particles

in the array not touching neighbors. The magnification of the

microscope is accurately determined using an i nterf erometr i cal 1 y—

calibrated line scale standard. As indicated in table 1 the

overall uncertainty is on the order of 0.1 to 0.2 Mm.

We have estimated the percentage of off—size large spheres

with diameters 30% greater than the average diameter by surveying

almost 7,000 spheres by optical microscopy. The space—shut tl

e

sample was found to have a slightly lower percentage of off-size

large spheres than the ground sample? 1.2 to 1.6% respectively

(see table 2). By observing the spheres in suspension with the

optical microscope we found that less than 0.1% of the spheres

were aggregated as doublets. Measurements with an electrical

sensing zone instrument (E-SZI) yielded the percentage of larger

particles, but this technique does not distinguish between 1 arge

Samp 1 e

Table 2. Number of Off—Size Particles

Large Part i cl es

a Large Particles S< b Aggregated*- Aggregated Doublets Doublets

Space 45/3612 1 . 2±0. 2% 1.9±0.7% <0.3%

Gr oun d 48/ 3048 1 . 6±0 . 2% 8 1 0/49600 1 . 6±0 . 1 % <0.1

%

a Large particles include all spherical particles with diameters

30% greater than the average size (approximately twice the

volume) as determined by optical microscopy,

b Results based on electrical sensing zone instrument,

c Results based on optical microscopy of spheres in suspension,

spherical particles and aggregated doublets. The results

14
obtained with the ESZI agree reasonably well with those tor the

optical microscope except that there appears to be slightly (nor

1 arge particles in the space shuttle sample. Because of the

experimental uncertainties and because of the small differences

in the percentage of off—size large spheres for the two samples

we can only say that both samples have about 1,5% (1 in 67

particles) off-size large spheres. For the optical case, the

limitation is the qualitative "eyeball" estimate of large spher

from low magni f i cat i on micrographs. Excellent statistics are

obtained by the ESZI with close to 50,000 spheres sized, but th

instrument uncertainty is much broader than the width of the si

distribution and there is some possibility of aggregates being

induced by the use of an electrolyte.

In addition to the off—size large spheres, we observe a large number of off—size small spheres with diameters in the

range 0,2—0.4 urn on many of the TEM micrographs (see fig. 2),

The relative percentage is not known. The particles seem to be

concentrated in certain regions. In some micrographs there are

as many off—size small spheres as average spheres.

5. Comparison with the Lehigh Results

The number—average size for the space shuttle sample, as

determined by V'anderhoff et a^, Ell, agrees quite well with the

NBS result (1,1% difference). However, the V’anderhoff et al^.

result for the ground sample is 10% low compared to our result.

Furthermore, while we find the average size of the groundproduced spheres to be about 0.2-0. 3 ym larger than the space

shuttle spheres by three independent techniques, the Vanderhcf t

15
et al_. results have the ground sample being smaller, not larger,

by about 0.3 ym.

Another difference between the results of the two

laboratories is in the value of the standard deviation for the

size distribution of the space-shuttle sample. The size

distribution obtained at NBS by TEM measurements is about two and

a half times smaller than the value obtained at Lehigh (see table

3). We believe that one reason for the discrepancy is that no

magnification distortion correction was made for the measurements

at Lehigh. We estimate the magnification distortion to be about

0.5% for diameter measurements made in the tangential direction

and 1.5% for measurements made in the radial direction. For an

area measurement, which is the basis of the Lehigh measurements,

we estimate the distortion to be the average, 1% or 0.050 ym.

Assuming the true <r to be 0.028 ym and using Vanderhoff et airs

estimate of the uncertainty in measuring the sphere’s image,

0.016 ym, we estimate sigma measured by the Lehigh method, s\ ,

Table 3. Comparison with Lehigh Resul t

s

Laboratory/Method Sample D (ym)

n

c (ym) ff / D (’ n

NBS/TEM

NBS/APS3 Space

Space

(5. 02) C

( 5 . 33

)

C

0.033

0.042

0.66

0.80

NBS/Opt i cal

Space 5.04

Lehi gh/TEM Space 4. 98 0. 082 1 . 64

NBS/TEM Ground (5. 18)

C

0. 151 2. 90

NBS/APS Ground (5. 55) C 0.201 3. 62

NBS/Opt i cal Ground 5.28

Lehi gh/TEM Ground 4.74 0. 167 3. 51

a Aerodynamic particle si zer

b Array sizing by optical mi croscopy

c Values for comparison purposes only

16
to be g 1 ven by the -foil owi ng -Formal a:

cr

! = l ( 0

.

050 )

(

0 . 028 ) ( 0 , 0

1

6) ^1

1 / ^ = 0 , 059 jum .

So it the magni f i cati on distortion of the Lehigh microscope is

similar to that of the NBS microscope, over half of the

difference between the Lehigh resalt and the NBS result can be

accounted for. We expect that part of the remaining discrepancy

results from the different criteria for excluding off-size

cl 95. We observed a decrease in when we started using a

5t I Col d i scor d an c y test. The differen c e i

n

rj between the

two laboratories for the ground sample is slight. This is to be

expected because the effect of the magni f i cat i on distortion

correction is not significant for the measurement of such a broad

size distribution.

In regard to the off—size spheres, our results agree

qualitatively with those of Lehigh. Both laboratories octal

n

about one large sphere per 70 average spheres for both samples.

Vanderhof f et a !_ at Lehigh find a slightly greater percentage of

1 ar ge part i cl es i n the ground samp 1 e. In our case the d i f f er ence

is not significant relative to our experimental errors. We also

observe off-size small particles smaller than the seed particles.

The presence of such particles is not discussed by Vanderhof

f

et al_.

o . L-Oncl usl o

n

it is pQSSi bis to d et er mi n e the sigma of a size distribut.

of 5 urn spheres with an uncertainty of about 0.006 urn by TEM.

this requires expertise in the use of the TEM, careful

17
magni f i cati on calibration, and careful diameter measurements.

This is time consuming and expensive.

On the other hand, we have demonstrated that the Aerodynami

Particle Sizer (APS) can size about 4,000 spheres in two minutes

with the statistics and plotting completed in another two

minutes. The resolution is almost as good as -for electron

microscopy for 5 ym spheres; in fact, it is twice as good as the

electron microscopy sizing method being used at Lehigh. We show

in Figure 5 the size distribution of nominal 10 and 15 urn PSL

spheres manufactured by Dvno (distributed by Dow), The increasein noise is probably due to water droplets that have not

evaporated. We believe that good results can be obtained for

particles at least as large as 15 ym by the proper selection of

nebulizer or sprayer together with an improved design of the

drying tube.

18
Number/Channel

Number/Channel

40

Nominal 10/im PSL

D n = 11.4,um

O! D n =1.1%

Diameter,//m

Diameter,^ m

Figure 5.

APS Size Distribution of PSL Spheres

19
Ref erences

Vanderhof -f , J. j El-fiasser, M, S, ; Micale, F, Ji Sudol , E.

D. j Tseng, C. M. ; Siluanowicz, A.; Kornfeld, D. M. ? and

Vicente, J. A. Preparation of large—particle-sizs

monod i sparse polystyrene latexes in microgravity. Submitte

for publication in Science.

Barnett, V.; Lewis, T. Outliers in statistical data. New

York, Wileyj 1973. p. 101.

J* Zelen, M. ; Severo, N. C. Probability functions. Chapter 26

in Handbook of hath emati cal Functions, M> Abramowitz and I.

Stegun, ed., New York, NY, Dover Publications, Inc. : 1965,

p. 941.

Remiarz, R. J,; Agarwal , J. K. ; Quant, F.

J. , Aerodynamic particle size analyzer, i mining and industrial work environments,

edited by V. A, iiarple and B. Y. H. Liu,

Publisher, Ann Arbor, Michigan (1933) p.

R« ; Si sd Bern, G, n Aerosols in the

V3 I nstr umentat i on

Ann Arbor Science

879-S95.

20
NBS-114A (REV. 2-«C> U.S. DEPT. OF COMM. 1. PUBLICATION OR

REPORT NO.

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

SHEET (See instructions) NBSIR 84-2914 JULY 1985

4. TITLE AND SUBTITLE

Sizing of Polystyrene Spheres Produced in Micrograyity

5. AUTHOR(S)

George Mulholland, Gary Hembree, and Arie Hartman

6. PERFORMING ORGANIZATION (If joint or other than N BS. see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9.

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

10.

SUPPLEMENTARY NOTES

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

11.

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

bibliography or literature survey, mention it here)

The standard deviation of the size distribution was determined for a polystyrene

latex produced in a space shuttle experiment and in an earth-bound control

experiment. Values determined from direct measurement of transmission electron

micrographs, corrected for magnification distortion, were 0.035 ym for the space

grown material and 0.15 ym for the control. The standard deviations obtained from

an aerodynamic particle sizer were only slightly greater than those obtained by

TEM; 0.042 ym and 0.20 ym for the shuttle and ground material respectively.

However these values were produced in a few hours versus the several weeks it took

for the electron microscopy. Both of the techniques used here resulted in

measured standard deviations significantly smaller than those previously reported

for this material.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by ->e~ :z aerodynamic particle sizing; particle counting; particle sizing; polystyrene latex;

optical array sizing; size distribution; size resolution; transmission electr n microscopy

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