Nat~onal Aeronautics and 

Space Adm~n~strat~on 

NASA TM -86487 

January 1985 

George C. Marshall Space Flight Center 

bldrshall Space Fl~ght Gel rrer, Alabama 35812 . -: 

Monodisperse 

' r a atex Reactor 

A Materials Processing 

Space Shuttle 

Mid-Deck Payload 

By Dale M. Kornfeld 

Space Science Laboratory 

(NASA-TPlwE6487) BONODISPBf SE LATEX REACTOR 

(IJLR) : A WATBBIALS FfiOCBSSING SPACE SHUTTLE 

MID-EYCR FAYLOAD (NASA) 16 p tic AOZ/flP A01 

CSCL 22A 

G3/12 - . -,.. . * - . ." . C1 ----. -. 2 .. 

Uncla s 

14542 
TECHNICAL REPORT STANDARD TITLE PAG 

fl. REPORT NO. 12. OaVRNYMT etSSION NO. 1 b. RECIPILIFt'S CATALOG 110. 

NASA TM-86487 I 

4. TlTLL AM0 SWTITLC 

Monodisperse Latex Reactor (MLR) - A Materials Processing 

Space Shuttle Mid-Deck Payload 

I George C. Marshai! Space Flight Center 

Marshall Space FligSt Center, Alabama 35812 

8. REPO(l1 DATE 

January 1985 

6. PERFMMING ORGANlZATlOW COaE 

Dale M. Kornfeld 

@. PERFORMING ORGANIZATION NW WO ABMCSS 

12. SPONSORING MitlKY MA- AN0 lOOMU I 

10. WORK ~~11 NO. 

I National Aeronautics and Space Admini strat ion 

Washington, D.C. 20546 

15. SUPPLEMLWTUY MOTES I 

Prepared by Space Science Laboratory, Science and Engineering Directorate. I 

18. ABSTRACT 

The Monodilperse Latex Reactor experiment has flown five times on the space 

shuttle, with three more flights currently planned. The objective of this project is 

to manufacture, in the microgravity environment of space, large part icle-size monodisperse polystyrene latexes in particle sizes larger and more uniform than can be 

manufactured on Earth. Historically it has been extremely difficult, if not impossible 

to manufacture in quantity very high quality monodisperse latexes on Earth in particle 

sizes much above several micrometers in diameter due to buoyancy and sedimentation 

problems during the polymerization reaction. However the MLR project has succeeded 

in manufacturing in microgravity monodisperse latex particles as large as 30 micrometers in diameter with a standard deviation of 1.4 percent. It is expected that 100 

micrometer particles will have been produced by the completion of the the three 

reiaaining flights. 

These tiny, highly uniform istex microspheres have become the "FIRST SPACE 

PRODUCT," that is, the first material ever to be commercially marketed that was 

manufactured in space. The U.S. National Bureau of Standards has certified the 

first batch of "space latex," which was transferred to NBS by NASA in July 1984, and 

they will begin marketing this material in mid-1985 as the U.S. national 10-micrometer Standard Reference Nater id. 

17. KEY WORDS 18. DISTRIBUTION STATEMENT I 

M~r~odisperse Latex Reactor (MLR) , Polystyrene Latex, Monodisperse Latex, 

Space Latex: Latex Microspheres. Space 

Processing, Microgravity Research 

Unclassified -- Unlimited 

'19. SECURITY CL \551f. (of :M. -part) 

I 

20. SECURITY CLASSIF. (of turn paw) 22. PRICE 

Unclassified Unclassified 15 NTIS + 

nFc - Form 3292 (Wr : W@) 

by pjauod T~e~~ Infonnatton Sarvlcc. S~rin~fi*idq VwLa SS161 

21. NO. OF PAGES 
TECHNICAL MEMORANDUM 

MONODISPERSE LATEX REACTOR (MLR) 

A Materials Processing Space Shuttle 

Mid-Deck Payload 

The Monodisperse Latex Reactor (MLR) is a Microgravity Science and Applications experiment, the purpose of which is to produce large particle-size monodisperse 

polystyrene latexes in microgravity in sizes larger than can be manufactured on Earth. 

A latex is a suspension of very tiny (micrometer-size) plastic spheres in water, 

stabilized by emulsifiers. The objective of this experiment is to grow llbillionsll of 

these microspheres to sizes larger than can be grown on Earth, while keeping all the 

spheres within the batch the same size and "perfectly" spherical. The word "monodisperse" means exactly the same size, and it is defined in this experiment as maintaining a standard deviation of diameter of less than 2 percent for all mAcrospheres 

in the batch. Thus far, latex batches have been returned to Earth after several 

shuttle flights with standard deviations better than 1.4 percent. 

The reason that high-quality monodisperse latex is so desirable is because a 

researcher need only examine or measure one particle at random from any batch and 

yet have confidence that all the other particles in the batch will be exactly the same 

size and will not need to be measured. This would be very important when the latex 

particles are used as size standards against which other objects in the same general 

size range are compared, or when they are used as membrane probes or as carriers 

for drugs or biological species that require extremely accurate knowledge of the 

voiume or surface area of the particles. 

A typical MLR latex reactor batch, such as that carried aboard its most recent 

shuttle flight (STS- 11) , produces 1.7 billion microspheres of 30 micrometers diameter, 

or 45 billion microspheres of 10 micrometers diameter; the difference in numbers is 

due to each latex recipe being held constant at about 25 percent total solids content 

by weight. The microspheres comprising these latexes can only be grown in quantity 

on Earth up to about 5 micrometers in diameter while remaining monodisperse due to 

buoyancy and sedimentation effects. They cannot be stirred sufficiently to maintain . the suspension during polymerization because stirring causes shear-induced coagulation which destroys the latex's monodisperse qualities and produces mostly coagulum. 

However, in microgravity the absence of buoyancy effects has thus far allowed growth 

of the spheres to 30 micrometers in diameter, and hopefully to much larger sizes in 

later flights. The MLR has now flown five times on the space shuttle (STS-3, -4, 

-6, -7, and -11), and three more flights are presently scheduled to be completed by 

mid-1986 (Table 1). 

This experiment has now produced the first commercial space product; i.e., the 

first commercial material ever to be marketed that has been manufactured in space. 

The 10 micrometer particle-size latex manufactured during the STS-6 shuttle mission 

was officially accepted by the U.S. National Bureau of Standards (NBS) on July 17, 

1984. After NBS completes certification of this latex in early 1985, they plan to 

market it to research workers worldwide as the United States national 10 micrometer 

Standard Reference Material. NASA transferred 15 grams of this 10 micrometer latex 

to NBS where it was diluted and packaged by NBS into 600 vials of 4 ml each. 
Each of these vials was priced by NBS at $384, thus giving the batch of 15 grams a 

total market value of $230,000. This computes to about $15,300 per gram of solid 

polymer, or some $434,000 per ounce. il^ the chemistry and all four reactors operate 

properly, about $2 to $3 million worth of latex can be manufactured during each 

space shuttle flight. NBS has also officially requested that NASA produce for them 

30 grams of 30 micrometer latex and 80 grams of 100 micrometer latex which they also 

plan to market. This is expected to be accomplished by the end of the next three 

flights. 

The MLR flight hardware is mounted in the shuttle mid-deck in place of three 

storage lockers as shown in Figure 1. The rectangular apparatus shown in Figure 2 

is the Support Electronics Package (SEP), and the round drum is called the Experiment Apparatus Container (EAC). Figure 3 shows the E-4C with its protective dome 

removed to display how the four separate independent chemical reactors are carried 

during each MLR flight. Each of these four reactors can produce a batch of 100 ml 

of latex by a process called seeded emulsion polymerization. The reactors are loaded - 

3 d,tys before launch with 100 ml each of the latex recipe, that is, the chemicals calculated to grow the desired large-size latex particles when the hardware is activated 

in space. A reactor consists of a small hollow steel cylinder with a stirrer at the 

bottom and a pistorl at the top. The piston moves to allow expansion and contraction 

of the latex as a function of temperature and conversion, and an LVDT monitors this 

movement. Heating tape is wrapped around the cylinder, and four thermocouples are 

mounted in it. Pre-programmed microprocessors within each reactor control its time 

and temperature profile. Once in space, the crew turns on the reactors and everything else is automatic. The reactors heat up and then stabilize at the desired hold 

temperature of 70°C, the chemicals inside slowly polymerize, and the temperature and 

volume-change data is read out as a function of time to a tape recorder inside the 

SEP. After 20 hours of operation the reactors turn themselves off. However, the 

crew must manually turn off the power supply and tape recorder. 

THE CHEMICAL PROCESS 

The MLR space latexes are manufactured by using as starting material the 

largest particle-size monodisperse latex that can be made on Earth, and then taking 

this "seed1' latex into the microgravity environment of space and doubling the diameter 

of each existing microsphere ir the latex without allowing any new microspheres to 

form. This product latex is then returned to Earth and examined microscopically to 

verify that the chemicals reacted as expected to generate the desired new larger-size 

monodisperse latex. If this new latex is determined to be of high quality - meaning a 

all the existing microspheres grew exactly the same amount - then this new product 

latex is taken back into space again and each microsphere is doubled in diameter 

again. Thus, the microspheres are doubled in diameter repeatedly during each 

succeeding flight until the final desired size is reached. See Figure 4 for transmission 

electron photomicrographs of the seed and product latexes from the STS-3 and -6 

missions, and Figure 5 for scanning electron photomicrographs of the seed and product i latexes from the STS-7 and - 11 missions. 

i It has not been possible so far to grow the seed spheres larger on each flight 

than a doubling of their diameter, because of current hardware and timeline limitations, without also producing large amounts of coagulum. However, it is expected 

that later improved hardware would be able to overcome this problem and allow 

increased seed growth in fewer steps. 
The original small-size seed particles are made on Earth by mixing together 

chemicals known as the monomer, the initiator, the emulsifier, and the inhibitors. 

The nonomer is the repeating unit of the chemical molecule styrene that links together 

end-to-end to polymerize into the long chain polystyrene polymer. The initiator is 

the chemical species that breaks down upon heating and causes the styrene monomer 

units to link together. The emulsifier is a soap-like material that stabilizes the particles by preventing them from sticking to:.:ether, and the inhibitors help to prevent 

the reaction from starting prematurely or new particles from forming in the water 

phase. When this mixture is heated, with gentle stirring, up to 70°C, the reaction 

starts and the latex particles begin to grow. Growth ceases when all the monomer in 

the system is converted to polymer. At this point each microsphere is usually about 

0.4 micrometers in diameter. 

To obtain larger particles, a carefully calculated amount of additional monomer 

is added at room temperature to the seed latex which has been prepc;ed as described 

above. The added monomer is absorbed equally by each of the existing seed particles, 

as if they were tiny sponges, causing them to swell to over twice their original 

diameter and become soft and sticky. Additional initiators, inhibitors, and emulsifiers 

are then added to this monomer-swollen latex, and it is heated again with gentle 

stirring to 70t'C. Once hot, the monomer inside each swollen seed particle begins to 

polymerize, causing each latex particle to actually shrink slightly as low-density 

monomer is being converted into high-density polymer, but resulting in each particle 

achieving a final net size increase to approximately twice its original diameter. 

Several of these sequential seeding steps can be performed on Earth with the product 

latexes remaining very monodisperse, until the particles grow to sizes above about 

2 or 3 micrometers. 

The process becomes very difficult, however, when larger sizes are attempted. 

High-quality monodisperse polystyrene latexes with particle sizes up to several 

micrometers in diameter are relatively easy to prepare on Earth; however, when the 

particles exceed this size range they tend to become polydisperse (all different sizes), 

or to coagulate, or both. This is due to various physical and chemical processes 

inherent in seeded emulsion polymerization systems. These include the sensitivity of 

the latexes to emulsifier concentration and mechanical shear (stirring). If the added 

emulsifier is insufficient to stabilize the growing latex particles, they will flocculate 

to form coagulum. If too much emulsifier is added, a new crop of tiny particles will 

be formed, along with the main crop of large ones, and the latex particle-size distribution will be bimodal (two different sizes) rather than monodisperse. 

At particle sizes well below 1 micrometer, the emulsifier concentration range is 

rather forgiving, but at larger sizes this operable range becomes smaller and smaller, 

until at sizes above 1 micrometer it becomes "knife-edge," meaning the reaction can go 

either way - make a good-quality monodisperse latex one time, and make a poorquality polydisperse latex usually with lots of coagulum the next time it is performed. 

As even larger sizes are attempted, the reaction always fails and gives only poorqu~lity polydisperse latexes. As one attempts to manufacture particles in sizes significantly larger than % 2 micrometers, the monomer- swollen particlzs have an increasing tendency to cream (rise to the top of the reaction pot) et the beginning of the 

reaction, and the partially-polymerized particles to settle out during the later stages 

of the reaction. This is due to the density difference between the particles and the 1 

water in which they are suspended, and because Brownian motion can no longer hold 1 them in suspension due to their large size. According to Stokes law, the terminal 

velocity of a sphere falling (or rising) through a fluid is directly proportional to the 

square of its radius and the difference in density between it and the fluid. As the 
3 polymerization proceeds, low-density styrene monomer (density = 0.905 glcm ) with 

which each seed sphere is saturated is converted into high density polystyrene poly3 mer (density = 1.05 glcm ). Since the polystyrene seed particles are swollen with at 

least six times their weight with additional monomer and thus their average density 

3 (ranging from about 0.95 to 0.92 glcm is now less than that of water, the swollen 

particles tend to cream before and during the early stages of the reaction (while they 

are full of monomer and thus lighter than water) and to settle during the later stages 

(when most of the monomer has been converted to polymer and they are heavier than 

water). Of course, stirring can be increased to oIfset this ?reaming and settling, 

but stirring at a rate sufficient to keep the particles in suspension usually results in 

coagulation because the large particles are very sensitive to mechanical shear. This 

means that if the particles are stirred too rapidly while they are polymerizing, they 

will hit each other and stick to form bunches or even huge lumps of coagulum. 

However, if the average density of the monomer-swollen particles were the same 

as that of the fluid they were suspended in, then creaming or settling would not 

occur. It would be possible to match the densities of the particles and the water 

phase at either end of the reaction by changing the monomer composition, such as by 

substituting a heavier monomer like p-chlorostyrene or vinyltoluene-t-butylstyrene 

mixtures for pure styrene, or by adding electrolytes or non-electrolytes to the water 

phase, but particle and fluid densities cannot be matched at the beginning, the end, 

aid continuously throughout the reaction due to the continuous change in density of 

the particles as they polymerize. If a heavier monomer is used for swelling, the 

particles could be made more closely neutrally buoyant at the beginning of the 

reaction, but being heavier, would settle more rapidly during the middle and later 

stages of the polymerization. 

Al! the particles must also be held at a constant and uniform temperature 

throughout the entire course of the reaction or, again, a poor-quality polydisperse 

product will be produced. If one portion of the latex reaction vessel varies more 

than 1 or 2OC, the particles in the hotter portion will grow slightly faster and therefore slightly larger than the particles in the cooler portion. The hottr , fastergrowing particles will actually rob monomer from the cooler, slower-growing particles. 

Therefore, due to these and other difficulties inherent in producing these 

large-particle monodisperse latexes on Earth, it was decided to perform the polymerization in microgravity where stirring could be held to the absolute minimum 

required for good heat transfer within the reactor. 

The series of chemical reactions by which liquid styrene monomer is converted 

into hard colorless polystyrene polymer can be shown as follows: When the initiator, 

Azobisisobutyronitrile (AIBN) in this case, is heated to 70°C it decomposes into two 

radicals (symbolized by R*) plus a molecule of nitrogen gas (N2) according to the 

equation : 

CH3 I CH3 I HEAT CH3 I 

AIBN 2 (R*) 
1 

One of the radicals (Re) then initiates the chain-building process, adding to a styrene 

monomer molecule 

by attacking its double bond. 

\ / I I R* + C=C - R-C-C* 

I 

The secondary carbon atom -C* is now highly reactive due to this attack and adds 

I 

another styrene molecule; and then this one adds another, and so on, building a long 

linear chain of styrene units 

H H 

R-C-C- + n L R-C-C 

I I 

H 4 H n 

until this growing chain meets another growing chain, or another (Re) and they join, 

thus stopping the growth and forming a molecule of polystyrene. 

Billions of these long chains of polystyrene are formed inside each existing latex seed 

particle, increasing its diameter to the desired new larger size. This can be represenied in the following drawing in which additional styrene monomer (M) and initiator 

(I) is dissolved inside the existing polystyrene seed particles and then polymerized 

by heating to increase the size of the particles: 

SEED PARTICLE SEED PARTICLE PRODUCT PARTICLE 
Note that each final product latex particle shrinks slightly from its monomer-swollen 

. . diameter, after all the monomer has been converted to polymer, but still exhibits a 

net increase of doubling its seed diameter if a ratio of about 611 monomer to polymer 

is used. 

Figure 6 graphically illustrates the difference in quality between the space-made 

latex (top photo) which was transferred to NBS, and the remaining portion of the 

same seed latex from the same bottle which was polymerized on Earth under identical 

conditions except for microgravity as a ground control (bottom photo). 

Once it is demonstrated that these large-size monodisperse latexes can be 

routinely produced in quantity and high quality, they can be marketed for many types 

of scientific applications. Biomedical research applications include such things as drug 

carriers and tracers in the body, human and animal blood flow studies, membrane and 

pore sizing in the body, and medical diagnostic tests. Other applications include use 

as calibration standards for ~pticiil and electron microscopes, Coulter counters, laser 

light-scattering equipment, and for many other types of laboratory equipment. 

This project was directed by Dr. John W. Vanderhoff, Principal Investigator 

(Lehigh University, Bethlehem, PA) along with Co-Investigators, Drs. Fortunato J. 

Micale and Mohamed S. El-Aasser (also of Lehigh University) and Dale M. Kornfeld 

(NASA/Marshall Space Flight Center). Two former graduate student research assistants, Drs. E. David Sudol and Chi-Ming Tseng, received their Ph.D. degrees at 

Lehigh University during the course of this program; and a third student, Mr. 

Anthony Silwanowicz, received his M.S. degree as part of this program. Their theses 

work represents all the chemical latex recipe research carried out during this program. 

This effort was sponsored by the Microgravity Sciences and Applications Division of 

the Office of Space Science and Applications, NASA Headquarters. The Prin.;ipl 

Investigator team research program was managed by NASAIMSFC , Huntsville, AL , under contract NAS8- 32951, initiated on February 22, 1978. Flight hardware development was also manage6 by NASAIRISFC. The MLR reactors and ground support equipment were decigned and manufactured by General Electric Company Space %vision, 

Philadelphia, PA, and the SEP and EAC cannister were designed and manufactured by 

Rockwell Internati~ilal Space Operations and Satellite Systems Division, Downey , CA. 
PUBLICATIONS 

U. S. Patent No. 4,247,434; issued January 27, 1981, llProcess for Preparation of 

Large-Particle-Size Monodisperse Latexes. l1 Inventors : J . W . Vanderhoff , F . J . Micale, M. S. El-Aasser, and D. M. Kornfeld. 

J. W. Vanderhoff, M. S. El-Ansser, F. J. Micale, E. D. Sudol, C. M. Tseng, A. 

Silwanowicz , and D . M. Kornfeld: Preparation of Large-Particle-Size Monodisperse 

Latexes in Space: The STS-6 and STS-7 Mission Reslts. Presented at AICHE 1984 

Summer Natic-lal Meeting, Philadelphia, Pennsylvania, August 19-22, 1984. 

J. W. Vanderhoff, M. S. El-Aasser, F. ,1 Micale, E. D. Sudol, C. M. Tseng, A. 

Silwanowicz, and D. M. Kornfeld: Preparation of Large-Particle-Size Monodisperse 

Latexes in Space: The STS-3, STS-4, STS-6, and STS-7 Mission Result:. Ir, Pmceedings of the Second Symposium on Space Industrialization, NASA CP- 231 3, er 

Camille M. Jernigaa (Huntsville, Alabama, February 13- 15, 19841, October 1984. 

J. W. Vanderhoff, M. S. El-Aasser, P. J. Micale, E. D. Sudol, C. M. Tseng, A. 

Silwanowicz , D . M . Kornfeld, and F . A. Vicente: Preparation of Large-Particle-Size 

Monodisperse Latexes in Space: Polymerization Kinetics and Process Development. 

Journsl of Dispersion Science and Technology, 5(3&4), 231-246 (1984). - 

Figure 1. STS accommodations for MLR. 
om.".?. :.. . . -# 

OF ROCR QilL';l! i % 
x 5 

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2~ 

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UW 

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a $ us z 

$3 g, E" v, 

m 0 

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35c 
2.5 p SEED 

3.4 )1 PRODUCT 4.1 P PRODUCT 5.0 p PRODUCT 

Recipe # 1 Recipe # 2 Recipe # 3 

-- --- 

5.b p SEED 

7.9 1 PRODUCT 10.0 p PRODUCT 

Recipc # 9 Recipe # 11 

Figure 4. Transmission electron photomicrographs of the MLR wed and pmduct 

latexes from thc STS-3 and STS-6 shuttle missions. 
7.9 )1 SEED 

. . 

13.1 p PRODUCT 16.6 p PRODUCT 17.88 PRODUCT 18.2~ PRODUCT 

Recipe # 13 Recipe # 14 Recipe # 15 Recipe # 16 

19.4 p PRODUCT 

Recipe # 20 

4 4 b4 

10.3 p SEED , , b4b4 1 17.8 p SEED 

30.4 p PRODUCT ,we9 p PRODUCT 

Recipe # 17 Recipe f 18 

Figure 5. Scanning electron photomicrographs of the MLH seed and product 

latexes from the STS-7 and STS-11 sh~ttle missions. 
Figure 6. Scanning electron photornict*ogt-;~p tls( 8005) of the 10 micrometer 

high-quality latex mnnubcturcrl in sp:~ cr ( tc 1) 1 ;I nd the corresponding 

ground-control latex (bottom) nit~nuf:ac:tz~rud on Earth under 

iden tical conditions I'rorn t hr! s:lrnc seed. except 

for * 1icrngr;nrity. 
TABLE 1. MLR FLIGHT SUMMARY 

Monomer / Pre /Process 

Flight No. Seed Product Polymer Stir Speed 

(Date) Recipe No. Size (p ) Size (\I ) Swell Ratio (rprn) Remar

STS-3 1 2.5 3.4 2 / 1 13/13 Very good prod

March 22, 1982 2 2.5 4.1 411 13/13 Very good prod

3 2.5 5.0 1011 13/13 Very good prod

4 0.19 0.26 211 13/13 Latex polymeriz

maturely; no 

recorded 

STS-4 5 5.5 7.5 211 13/13 An electrical fe

June 27, 1982 6 5.5 9.0 411 13/13 SEP prevented 

7 5.5 9.3 5.711 13/13 reactors from h

8 5.5 10.8 6.211 13/13 perly and all f

were only parti

merized ; theref

usable product 

STS-6 9 5.6 7.9 211 13/13 Excellent produ

April 4, 1983 as seed for R

10 5.6 4 / 1 13/13 This reactor fa

-- 

thus no prod

ll* 5.6 10.0 611 13/13 Excellent produ

FIRST SPACE 

12 0.19 0.26 211 13/13 Repeat of Recip

duct not full

STS- 7 13 7.9 13.1 611 13/13 Excellent produ

June 18, 1983 14 10.3 16.6 411 13/13 Excellent produ

15 10.3 17.8 611 1316 Excellent produ

as seed for R

16 10.3 18.2 611 613 Excellent produ

new slower stir 

r 

STS-11 17 17.8 30.4 5 / 1 1316 Excellent produ

February 3, 1984 18 17.8 30.9 511 613 Excellent produ

19 10.3 18 611 Reactor appare

tamined; mos

20 10.3 19.4 6 / 1 6 / 3 

*The 10 micrometer product latex from Recipe #11 was transferred to the National Bureau o

Standards on July 17, 1984, and certified for sale in April 1985, thus becoming the fir

"product" to be manufactured in space and marketed on Earth. NBS determined this latex 

to have 1.1% std. dev. of diameter. 
APPROVAL 

MONODISPERSE LATEX REACTOR (MLR) 

A Materials Processing Space Shuttle 

Mid-Deck Payload 

By Dale M. Kornfeld 

The information in this report has been reviewed for technical content. Review 

of any information concerning Department of Defense or nuclear energy activities or 

programs has been made by the hlSFC Security Classification Officer. This report, 

in its entirety, has been determined to be unclassified. 

Director ,upace Science Laboratory 

*u.S. GOVERNMENT PRINTING OFFICE 1981-W4-WEI10114 

a ~-*Pv./