Determination of particle size of soft polymer dispersions by electron microscopy

L E T T E R S TO T H E ED I TO RS interaction of cationics with pyrrolidone or hydroxy groups, but to that with acetate or butyral parts together with the hydrocarbon backbone. Thus it seems plausible that the hydrophobic bond between the acetate or butyral segments in water is weakened by introduction of the hydrophilic groups into the polymer chain, leading to over-all uncoiling of the copolymers even by the cationic surfactants. ACKNOWLEDGMENTS The authors wish to thank Nippon Synthetic Chem. Co. and Sekisui Chem. Ind. Co. for supply of the experimental materials. REFERENCES 1. SAITO, S., Kolloid-Z. 158, 120 (1958). 2. S~ITO, S., Kolloid-Z. Z. Polymere, 215, 16, (1967). 3. SAITO, S., J. Soc. Japan Oil Chemists, 12, 133 (1963). A review. 4. SATA, N., AND SAITO, S., Kolloid-Z. 128, 154 (1952). 5. PRINS, W., AND HERMANS,J. J., Koninkl. Ned. Akad. Wetenschap. Prec. Ser. B 59, 298 (1956). 6. ISEMURA, T., AND IMANISHI, A., J. Polymer Sci. 33, 337 (1958). 7. BOTI~:~, C., DE MAI~TIIS, F., AND SOLINAS,M., J. Phys. Chem. 68, 3624 (1964). 8. MARUTA, I., A ~ I , H., A~D hD~, A., J. Colloid and Interface Sci. 22, 294 (1966). 9. S~TO, S., Kolloid-Z. 133, 12 (1953). 1O. SAITO, S., J. Colloid Sci. 15, 283 (1960). SHUZI SAITO YOSHIO MIZUTA

Momotani Juntenkan, Ltd., Minato~u, Osaka, Japan Received January 3, I967

Determination of Particle Size of Soft Polymer Dispersions by Electron Microscopy Two years ago a technique was reported in this journal (1) for determining the particle size of film-forming latices by electron microscopy. The

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method is based on the sorption of a small amount of styrene monomer into the latex particles, followed by polymerization in situ with gamma radiation. I should like to report a modification of this technique that has been used successfully in our Laboratories. As in the original procedure, the latex is diluted to approximately 5% solids and a quantity of monomer is added and dispersed, which is equal to about 10% of the polymer weight. However, after the monomer has been sorbed into the latex particles, it is polymerized in situ, by using X-rays rather than by gamma radiation as originally reported. All samples, 20 ml. in size, were irradiated in a nitrogen atmosphere with a 50-kilovolt BrackeSeib X-ray machine. The samples were agitated with a magnetic stirrer to ensure uniform exposure. All samples were irradiated for 2 hr. at a dose rate of about 1.5 mega-roentgens per hour. The absorbed dose was not determined. This procedure was used in the study of a series of particularly soft acrylic polymer dispersions. Without treatment, these materials gave electron micrographs which were virtually useless for the determination of particle size. However, when the polymer samples were hardened, particles as small as 400A were well defined, and particles 100A to 200A in diameter were clearly visible. Both styrene and a styrene-divinylbenzene mixture were used as the added monomer, the latter giving slightly better results. The author wishes to acknowledge the assistance of Dr. J. L. Donovan, for the irradiation of various samples, and of Mr. C. F. Oster, Jr., who prepared the electron micrographs. REFERENCES

1. ¥-ANZO, E., MARCHESSAUL% R. M., AND STANNETT, V., J. Colloid Sci. 19, 578 (1964). NEAL E. ~ORGANSON Research Laboratories, Eastman Kodak Company, Rochester, New York 14650 Received January 26, 1967