Surface Phase Transition of Associating Fluids on Functionalized Surfaces

Abstract

Surface phase transitions are studied for Lennard-Jones (LJ) based dimer forming associating fluids on modified surfaces with active sites for various association strengths using grand-canonical transition matrix Monte Carlo. We examine adsorption isotherm, density, energy, and monomer profiles to differentiate layering, quasi-2D vapor–liquid and prewetting transitions. Prewetting transition is found for association strengths: εaf = 8 and 10, whereas, for weaker associating fluids, εaf = 4 and 6, we observe quasi-2D vapor–liquid transition. The growth of thick films in the case of quasi-2D vapor liquid transitions is found to suppress with decrease in temperature and eventually splits in layering transitions. For systems exhibiting prewetting transition, wetting temperature and prewetting critical temperature increase with increasing association strength. In addition, we examine boundary tension of quasi-2D and prewetting transitions using finite size scaling formalism of Binder. Our results indicate that the quasi-2D boundary tension is lower than that of the prewetting transition. Surface sites are found to reduce the boundary tension; however, the effect of active sites diminishes with stronger fluid–fluid associating strength.