Equilibrium correlations in interfaces between two immiscible liquids

Abstract

Static density and concentration correlations in momentum space are determined quantitatively in molecular dynamics computer experiments on the interface between two liquid phases of a binary mixture. The interaction between spherical particles of equal sizes is modeled by 6–12 Lennard-Jones potentials. The resulting four density-density correlations are inverted to four direct correlation functions. Transformation to density-concentration variables inspired by the Bhatia–Thornton transformation and the hitherto unknown characteristic shapes of their projections, including the generalization of the Yvon–Zwanzig–Triezenberg projection, are discussed in detail; it is demonstrated that the q4 coefficient again is negative. This precludes its interpretation as a rigidity coefficient. The interfacial contributions decay rather quickly with the momentum q, becoming totally submerged by short-range bulk and bulklike fluctuations at q-values of the order of 1/5 of the q-value of the nearest-neighbor (first) peak in the scattering factor.