The wetting of planar solid surfaces by symmetric binary mixtures near bulk gas–liquidcoexistence

Abstract

We investigate the wetting of planar, nonselective solid substrates by symmetric binary mixtureswhere the attraction strength between like molecules of components A and B is the same, that isϵAA = ϵBB<0. Mixture properties come about by varying , that is by varying the attraction between a pair of unlike molecules. By means of mean-field latticedensity functional calculations we observe a rich wetting behaviour as a result of the interplay betweenϵAB and the attraction of fluid molecules by the solid substrateϵW. In accord with previous studies we observe complete wetting only above the critical endpoint if the bulk mixture exhibits a moderate to weak tendency to liquid–liquid phaseseparation even for relatively strong fluid–substrate attraction. However, in this caselayering transitions may arise below the temperature of the critical end point. For stronglyphase separating mixtures complete wetting is observed for all temperatures along the line of discontinuous phase transitions in the bulk.