Wetting at a fluid–wall interface. Computer simulation and exact statistical sum rules

Abstract

We report on a search by computer simulation to locate an example of a wetting transition at a fluid–wall interface, namely, the transition between partial wetting and complete ‘wetting’ by vapour at a weakly attractive wall in the presence of bulk liquid–vapour coexistence, for a system with strictly finite-range interactions. In addition, general statistical-mechanical theory with direct application to wetting phenomena is described and used to interpret simulation results. Our data clearly show the presence of a first-order wetting transition at a moderately attractive wall, particularly when analysed with the help of statistical-mechanical sum rules. Both theory and simulation indicate that our type of wetting transition is qualitatively influenced by the local fluid structure at the wall. We also find that simple fluctuation theory yields a semi-quantitative description of our results. In the partial wetting region, the surface tension data are consistent with a first-order wetting transition at the point indicated by the adsorption results and with the prediction of an exact statistical sum rule for the variation of the contact angle with wall strength.