Abstract
Within self-consistent field theory we study the phase behaviour of a symmetric binary AB polymer blend confined into a thin film. The film surfaces interact with the monomers via short-range potentials. One surface attracts the A component and the corresponding semi-infinite system exhibits a first-order wetting transition. The surface interaction of the opposite surface is varied as to study the crossover from capillary condensation for symmetric 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 case the phase diagram exhibits two critical points which correspond to the prewetting critical points of the semi-infinite system. The cross over 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.