Molecular theory of fluid interfaces

Abstract

A new description of fluid interfaces, the local correlation model, is developed in a gradient approximation to the interfacial density distribution but otherwise rests on fewer assumptions than either the modified Van der Waals model or Toxvaerd's mean field perturbation theory, with both of which it is compared. Its numerical predictions agree quantitatively with those of the modified Van der Waals model for a Lennard-Jones fluid. The differential equation for the density profile, which results from the gradient approximation, provides a particularly simple description of an interface: the intermolecular contributions to interface structure are divided among (1) interactions occurring in homogeneous fluid, and (2) interactions peculiar to inhomogeneous fluid, the latter being represented by an influence factor c and the total thermodynamic potential density ω of inhomogeneous fluid. Numerical results indicate that for a wide range of temperatures the differential equation gives interfacial density profiles and tensions in good agreement with the more rigorous integral equations.