The liquid–vapor interface of simple polar fluids. I. Integral equation and perturbation theories

Abstract

The structure and surface tension of the liquid–vapor interface of a polar fluid are investigated using integral equation and perturbation theories. A recently introduced integro-differential equation and a perturbation theory are employed to determine the extent to which purely multipolar anisotropies in the pair potential induce orientational ordering. Both of these theories agree that orientational ordering can be induced at the liquid–vapor interface by purely multipolar anisotropies in the intermolecular potential. The Yvon–Born–Green equation and the virial equation for the surface tension are written in terms of the spherical harmonic coefficients of the one and two particle distributions, and simple expressions are obtained for the density profile and the anisotropic contribution to the surface tension for molecular models of multipolar symmetry. The density profiles, density-orientation profiles, surface thickness, and surface tension are calculated for the Stockmayer fluid for a range of temperatures and dipole moments.