  When systems that can undergo phase separation between two coexisting phases
in the bulk are confined in thin film geometry between parallel walls, the
phase behavior can be profoundly modified. These phenomena shall be described
and exemplified by computer simulations of the Asakura-Oosawa model for
colloid-polymer mixtures, but applications to other soft matter systems (e.g.
confined polymer blends) will also be mentioned. Typically a wall will prefer
one of the phases, and hence the composition of the system in the direction
perpendicular to the walls will not be homogeneous. If both walls are of the
same kind, this effect leads to a distortion of the phase diagram of the system
in thin film geometry, in comparison with the bulk, analogous to the phenomenon
of "capillary condensation" of simple fluids in thin capillaries. In the case
of "competing walls", where both walls prefer different phases of the two
phases coexisting in the bulk, a state with an interface parallel to the walls
gets stabilized. The transition from the disordered phase to this "soft mode
phase" is rounded by the finite thickness of the film and not a sharp phase
transition. However, a sharp transition can occur where this interface gets
localized at (one of) the walls. The relation of this interface localization
transition to wetting phenomena is discussed. Finally, an outlook to related
phenomena is given, such as the effects of confinement in cylindrical pores on
the phase behavior, and more complicated ordering phenomena (lamellar
mesophases of block copolymers or nematic phases of liquid crystals under
confinement).

Soft Condensed Matter;Materials Science