Interplay between wetting and miscibility in thin binary polymer films Original Research Article

We study the interplay between wetting and miscibility of a symmetric AB polymer mixture via Monte Carlo simulations and numerical self-consistent field calculations. The crossover between capillary condensation in films with symmetric surface fields and interface localization/delocalization transition in films with antisymmetric boundaries is studied. In the latter case the phase diagram exhibits two critical points which correspond to the prewetting critical points of the semi-infinite system. The crossover between these qualitatively different limiting behaviours occurs gradually; however, the critical temperature and the critical composition exhibit a non-monotonic dependence on the surface field. We study the dependence of the phase diagram on the film thickness Δ for antisymmetric surface fields. Upon decreasing the film thickness the two critical points approach the symmetry axis of the phase diagram, and below a certain thickness Δtri, there remains only a single critical point at symmetric composition. This corresponds to a second order interface localization/delocalization transition. At Δtri tricritical behaviour is found and the rich crossover behaviour is investigated by Monte Carlo simulations.