Wetting behavior of associating binary mixtures at attractive walls: a lattice Monte Carlo study

The lattice gas model is used to study the effects of molecular association on the wettability of surfaces with attractive walls by binary symmetric associating mixtures. The model assumes that the adsorbate particles occupy a regular cubic lattice of sites and that the interactions between adsorbate particles involve only the first nearest neighbors. The energies of interaction between the pairs of like particles are the same, while the only interaction between a pair of unlike particles is due to association. Only the formation of dimers is allowed and the energy of association is finite. The particles are subject to the surface, van der Waals-like potential, assumed to be the same for both components. The model is studied with the help of the Monte Carlo simulation method in the grand canonical ensemble. Only the ground state properties are treated analytically. It is demonstrated that, in general, molecular association hinders wetting. In particular, in the systems with nonzero wetting temperature, the increase of the association energy leads to the increase of the wetting temperature and for sufficiently high energy of association the mixture does not wet the surface at all. When the system is expected to exhibit complete wetting at the ground state, the film formed by strongly associating mixtures wets the surface only at sufficiently low temperatures, below the dewetting temperature. It is demonstrated that the dewetting temperature increases with the strength of the surface potential as well as with the increase of the association energy.