Reentrant miscibility in two-dimensional symmetrical mixtures

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.

Effects of geometrical and energetic nonadditivity on the phase behavior of two-component symmetric mixtures

Using Monte Carlo simulation methods in the grand-canonical ensemble, we have studied the phase behavior of three-dimensional symmetric binary mixtures of Lennard-Jones particles. We have also elucidated the effects of geometric and energetic nonadditivity on the phase behavior. Phase diagrams for several systems have been evaluated. We have demonstrated that in completely miscible mixtures the geometrical nonadditivity (negative as well as positive) stabilizes a liquid phase leading to a gradual increase of the critical temperature. The mechanism leading to such behavior is different when the system shows negative and positive geometrical nonadditivity. In the case of systems with negative energetic nonadditivity, which may exhibit demixing transition in the liquid phase, their phase behavior is also strongly affected by the geometric non-additivity. The systems with negative geometric nonadditivity have been demonstrated to show reentrant miscibility, while those with positive geometric nonadditivity show enhanced tendency toward mixing at sufficiently high temperatures. We have evaluated phase diagrams for several systems.