Structure of the liquid/vapour and liquid/solid interfaces

Abstract

A theoretical method of determining the density profile ρ⁽¹⁾(z) at liquid/vapour and liquid/solid interfaces is developed, based on a procedure of Helfand, Frisch and Lebowitz. The density profile for a given fluid is shown to be related to the value of the pair distribution function g₁₂ ⁽²⁾(r) for a two component fluid in the limit that the molecular radius of the second component becomes infinitely large (i.e. macroscopic) and its density vanishes. The density profile for hard spheres against a hard interface is obtained in the P.Y. approximation. The extension to the liquid/vapour interface is discussed and the free-interfacial density profile for a fluid with an attractive inverse sixth power pair potential is displayed. A comparison is made with other modern theories.