Monte Carlo simulation of polymer mixtures:: recent progress

The phase diagram of symmetrical polymer blends (A, B) confined into thin films is studied, considering both the effect of finite film thickness D and of surface forces at the confining walls that either prefer both the same species, or different species. In the case of "neutral" walls confinement enhances the compatibility of the blend. The critical temperature is depressed, the coexistence curve gets flattened (reflecting a crossover from 3-dimensional to 2-dimensional critical behavior). But if both walls preferentially attract species A, then also the critical composition of the blend is shifted to the A-rich side of the phase diagram, and the coexistence curve exhibits a bulge just above the wetting transition temperature. If one wail attracts A and the other B, lateral phase separation sets in via a first order transition. Above this transition, an interface parallel to the walls is stabilized in the system.