RESLNOGKAPHY 





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Fig. 4. Polyacrylonitrile as thin, self-support- 

 ing film cast from dilute solution in ethylene 

 carbonate. Shadowed at 10° with U and electron 

 micrographed. Shows Type I particles some as 

 monolayers partially covering holes (broken bub- 

 bles) in the film. 72,000X 



ilarly in natural or synthetic latices, emul- 

 sions and suspensions, the colloidal particles 

 are involved in failures such as by freezing, 

 in consolidation such as by smoking natural 

 rubber latex or in performance such as in 

 painting or printing. Particles of Type II 

 may be perceptible light microscopically and 

 generally are perceptible electron micro- 

 scopically. 



Type III. These may be aggregates of 

 Type II particles. (Figure 7) More and more 

 resins are being formulated to meet useful 

 specifications by "alloying" two or more 

 phases of the same or different component 

 (monomer) in a system. For example, a latex 

 may be added sometime during the poly- 

 merization of styrene to make a more im- 

 pact-resistant material. (Figure 8). During 

 the consolidation with polystyrene the rub- 

 bery colloidal particles may be greatly en- 

 larged or a rubbery phase may be milled 

 into an adliesive to give resilience to the 

 finished joint. A crystalline phase may be 

 introduced to a system to give rigidity. 

 That is particles of Type III may be amor- 

 phous or crystalline and of the same or differ- 

 ent stereoisomer. The amorphous phase (s) 

 may be in the rubbery and/or glassy states 

 (Figure 9). 



Type III particles and parts are generally 

 visible in the light microscope. It should 

 provide illumination as bright-field or dark- 

 field, by transmitted or reflected light, 

 polarized or unpolarized, as needed. Ability 

 to change from one kind of illumination to 

 another should be quick and easy (1, 2). 



Figs. 5(A) Emulsion polymerized polyacrylo- 

 nitrile, as dried and electron micrographed. Type 

 II particles, useful as a latex or in consolidation. 

 34,000X . 



(B) Same polj^mer after pressure-molding and 

 fracturing. Positive electron micrograph of replica 

 shows that resin came apart between same type of 

 particles as were molded together. 34,000X . 



528 



