Surface and bulk ordering in thin films

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Abstract
Recent experiments that probe the effect of confinement on the dynamical properties of thin liquid films have shown that these films undergo an abrupt transition to a solid below a critical thickness. To model this behavior, we present a mean-field theory for confinement-induced first-order phase transitions based on a Ginzburg-Landau type expression for the free-energy. We show how the equilibrium melting temperature increases as the film thickness is decreased; for thick films, the melting temperature approaches its bulk value. The predicted phase diagram includes three phases: an ordinary liquid (where both the surface layer and the bulk of the film are liquid), a crystalline solid phase (where both the surface layer and the bulk are ordered) and a quasi-liquid phase in which the bulk of the film is liquid-like but the surfaces are ordered. Transitions between the phases are always first order.