Highly non-additive symmetric mixtures at a wall.

This paper discusses the results of the grand canonical ensemble Monte Carlo simulation of the wetting behavior of non-additive symmetric mixtures at non-selective walls. We have focused on the mixtures that exhibit closed immiscibility loops in the bulk, and the results obtained have demonstrated that such systems show a rather complex wetting behavior. In particular, such mixtures may exhibit a complete wetting at temperatures below the bulk demixing point, and an incomplete wetting at higher temperatures. Such a situation occurs when the adsorbed film remains mixed up to the bulk coexistence. However, close to the bulk tricritical point, being the onset of the continuous demixing transition (λ-line), a second wetting transition takes place. On the other hand, in the systems in which the adsorbed films undergo the demixing transition, a complete wetting may occur below as well as at and above the bulk demixing transition temperature. It has also been demonstrated that the wetting behavior depends strongly on the strength of the surface-fluid interaction.