Leopold Infeld Colloquium

The equilibrium structure and phase behaviour of fluids in confining geometries are significantly richer than in the corresponding bulk system. Combined effects of finite size and substrate-fluid interactions can lead to a variety of phenomena including capillary condensation and evaporation (associated with shifting of bulk first order transitions), layering and pre-wetting, as well as phenomena associated with bulk critical fluctuations such as the critical Casimir effect. This lecture will focus mainly on the simplest geometry :simple fluids confined in open slits where the two parallel walls are either (i) identical or (ii) exert different external fields so that one wall is attractive and is wet by liquid (solvophilic) while the other is repulsive and may be dry i.e. wet by the gas phase (solvophobic). In case (ii) a 'delocalized interface phase' can form which exhibits striking fluctuations. We investigate the properties of this unusual phase using an effective interfacial Hamiltonian approach and a microscopic (classical) density functional theory of inhomogeneous liquids. We mention recent work on other types of confinement.