The local structure factor near an interface; beyond extended capillary-wave models

We investigate the local structure factor S (z;q) at a free liquid-gas interface in systems with short-ranged intermolecular forces and determine the corrections to the leading-order, capillary-wave-like, Goldstone mode divergence of S(z;q) known to occur for parallel (i.e. measured along the interface) wavevectors q -> 0. We show from explicit solution of the inhomogeneous Ornstein-Zernike equation that for distances z far from the interface, where the profile decays exponentially, S (z;q) splits unambiguously into bulk and interfacial contributions. On each side of the interface, the interfacial contributions can be characterised by distinct liquid and gas wavevector dependent surface tensions, sigma(l)(q) and sigma(g)(q), which are determined solely by the bulk two-body and three-body direct correlation functions.

statistical mechanics; capillary waves; fluid interfaces; surface tension; liquid-vapor interface; der-waals model; fluctuation theory; surface-tension; wetting transitions; density profile; critical-point; length scales; fluids; approximation

The local structure factor near an interface; beyond extended capillary-wave models Articles