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The film thickness dependence of surface structure for immiscible polystyrene/poly(methyl methacrylate) (PS/PMMA) films was investigated on the basis of atomic force microscopic observation and X-ray photoelectron spectroscopic measurement. In the case of the PS/PMMA film of 25 μm thickness, the air−polymer interfacial region was covered with a PS rich overlayer due to its lower surface free energy compared with that of PMMA and a well-defined macroscopic phase-separated structure was formed in the bulk phase. Also, in the case of the PS/PMMA thin film of 100 nm thickness, the phase-separated structure, in which the PMMA rich domains separated out of the PS rich matrix, formed at the film surface. The formation of the surface structure for the PS/PMMA thin film can be attributed to either the chain conformation or chain aggregation structure being frozen at the air−polymer interfacial region before the formation of a PS rich overlayer due to the fairly fast evaporation of solvent molecules. On the other h...
Tanaka et al. (Mon,) studied this question.