THERMODYNAMICS OF THIN FLUID FILMS

When fluids are confined within narrow spaces, their phase equilibria, structural, and dynamical properties become quantitatively and qualit atively different from their bulk values. The conditions obtained at t hermodynamic equilibrium between a thin film and bulk fluid are derive d in this paper. It is shown that the film thickness and film tension are new thermodynamic parameters. Because the thin film has properties distinct from that of the bulk fluid, it is possible for fluid to exi st along planar boundaries even for systems characterized by non zero dihedral angles. For a stable thin film to exist, it is necessary that the ''disjoining pressure'' be positive or replusive. An analysis of the disjoining pressure for a basalt melt-peridotite system indicates that a thin basalt liquid film may exist at interphase boundaries.