Non-monotonous crossover between capillary condensation and interface localisation/delocalisation transition in binary polymer blends

Within self-consistent field theory we study the phase behaviour of a symme tric binary AB polymer blend confined into a thin film. The film surfaces i nteract with the monomers via short-range potentials. One surface attracts the A. component and the corresponding semi-infinite system exhibits a firs t-order wetting transition. The surface interaction of the opposite surface is varied as to study the crossover from capillary condensation for symmet ric surface fields to the interface localisation/delocalisation transition for antisymmetric surface fields. In the former case the phase diagram has a single critical point close to the bulk critical point. In the latter cas e the phase diagram exhibits two critical points which correspond to the pr ewetting critical points of the semi-infinite system. The crossover between these qualitatively different limiting behaviours occurs gradually; howeve r, the critical temperature and the critical composition exhibit a non-mono tonic dependence on the surface field.