(175d) Phase Behavior of Associating Fluids in Contact with a Solid Surface

Interaction of fluids with solids in terms of confinement or near the surface is natural phenomena in our daily life. Influence of solid interaction not only change the fluid properties(critical properties, free energies etc) but also induce different phase transitions such as layering, prewetting and capillary condensation. The occurrence of these phases depends on relative strength of fluid-fluid and fluid-solid interaction.

In this work, we present a systematic study of the prewetting behavior of Lennard-Jones based dimer forming associating fluids on a model solid CO₂ surface for various associating strengths using grand-canonical transition matrix Monte Carlo (GC-TMMC) and histogram reweighting techniques. Occurrences of prewetting transition is observed for associating strengths ranging from ε_af =2.0, 4.0, 6.0, 8.0 and 10.0. Wetting temperature, T_w, increases with associating energy and attains a maxima at a moderate associating strength. Further increase in associating energy decreases the wetting temperature, which is in contrast to the DFT prediction. Critical prewetting temperature, Tpwc, on the other hand, always increase with association energy. Boundary tension of thin-thick film via GC-TMMC and finite size scaling is found to increase at a constant T/T_pwc with increasing association strength up to 8.0. Subsequent increase in associating strength decreases the boundary tension, which is akin to the behavior of the vapor-liquid surface tension of bulk associating fluids. We also report structural, orientation order and monomer fraction of the thin and thick films of associating fluids.