Abstract
The Monte Carlo simulation method in the grand canonical ensemble has been used to study the wetting behavior of highly non-additive symmetric mixtures in contact with selective walls. We have focused on the behavior of the mixtures, which exhibit closed immiscibility loops in the bulk, and have investigated the interplay between the surface selectivity and the wetting properties of the adsorbed mixtures. Different wetting behaviors has been found, depending on the values of the adsorption energies of the mixture components. We have considered the systems in which the wetting at non-selective walls occurs at the temperatures below the onset of the demixing transition in the bulk. When the average value of adsorption energies is fixed, the wetting temperature has been found to be unaffected by the weak selectivity of the wall. In this case, the reentrant mixing has been observed in thick adsorbed films. However, when the wall selectivity increases beyond a certain threshold value, the reentrant mixing in the film has been suppressed. This leads to the increase of the wetting temperature. In the case, when the adsorption energy of one component is fixed, while the adsorption energy of the second component changes, the wetting temperature has been found to exhibit non-monotonous changes with the difference between the adsorption energies of the mixture components.
Highlights
It has been demonstrated [8] that when the parameters e and s are both considerably smaller than unity, the symmetric mixtures may exhibit closed immiscibility loops in the liquid phase
The wetting temperature decreases when ε∗gs becomes larger, and for ε∗gs equal to and higher than about 6, the wetting has been found to be pinned in the triple point Tt∗r,v−ml−ms ≈ 0.865, in which the vapor coexists with the mixed liquid and the mixed solid phases
We have attempted to elucidate the interplay between the properties of bulk highly non-additive symmetric mixtures, with the parameter e = 0.6, and their wetting behavior at selective walls
Summary
It has been demonstrated [8] that when the parameters e and s are both considerably smaller than unity, the symmetric mixtures may exhibit closed immiscibility loops in the liquid phase. The study of wetting behavior of energetically and geometrically non-additive mixtures, with e < 1 and s < 1, at non-selective walls, has concentrated on the systems, which exhibit closed immiscibility loops in the bulk [32] In such cases, the vapor condenses into the mixed liquid at low temperatures, and into the demixed liquid at the temperatures above the triple point, Ttr,v−ml−dl, in which the vapor coexists with the mixed and demixed liquids. The AB pairs are preferred in particular when the density is high These two effects lead to the stabilization of mixed films, even when the chemical potential approaches the bulk coexistence, and the temperature is higher than Ttr,v−ml−dl.
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