Electron Microscopy of Heterogeneous Elastomer Blends

Abstract

Abstract Microheterogeneity has been observed in several elastomer blends on thin frozen sections, microtomed in a nitrogen atmosphere to eliminate all surface oxidation and cracking, in both phase and electron microscopes. Phase photomicrographs and electron micrographs showing identical detail were obtained on sections swollen in a solvent. During sample preparation the swollen sections are stretched. Samples are examined, after solvent evaporation, in the stretched state. Stereomicrographs of palladium shadowed carbon replicas of the sections indicated that the contrast in electron microscopy corresponds to thickness differences in the sections. These thickness differences were shown to be directly related to the differences in swelling characteristics of the individual elastomer microphases. By using a nonswelling liquid, no phase differences could be observed. By allowing the stretched sections to retract, phase differences diminished to almost complete disappearance. Heterogeneity exists in many elastomer blends. In SBR blends with polybutadiene, however, heterogeneity was observed only in the initial mixing stage, but complete compatibility was found to exist upon continued mixing. The interpretation of electron micrographs of blends loaded with carbon blacks is more complex, since swelling characteristics of the elastomer phases are altered by the presence of a reinforcing filler. No evidence was found for large scale phase transfer of carbon black.