  We study the interplay between wetting and miscibility of a symmetric polymer
mixture via MC simulations and SCF calculations. The film surfaces interact
with the monomers via short ranged potentials and the wetting transition is of
first order. If both surfaces in a film attract the same component, capillary
condensation occurs and the critical point is close to the critical point of
the bulk. If surfaces attract different components, an interface localization
occurs which gives rise to phase diagrams with two critical points in the
vicinity of the pre-wetting critical point. The crossover between these two
types of phase diagrams as a function of the surface field asymmetry is
studied. We investigate the dependence of the phase diagram on the film
thickness D 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 D_tri there remains only a single
critical point at symmetric composition. This corresponds to a second order
interface localisation transition even though the wetting transition is of
first order. At a specific film thickness, D_tri, tricritical behavior is
found. The behavior of antisymmetric films is compared with the phase behavior
in an antisymmetric double wedge. While the former is the analogon of the
wetting transition of a planar surface, the latter is the analogon of the
filling behavior of a single wedge. We present evidence for a second order
interface localization transition in an antisymmetric double wedge and relate
its unconventional critical behavior to the predictions of Parry et al. PRL 83
5535 (1999) for wedge filling. The critical behavior differs from the Ising
universality class and is characterized by strong anisotropic fluctuations.
