Phase Behaviour of Confined Associating Fluid in a Functionalized Slit Pore: A Monte Carlo Study

Abstract Vapor-liquid phase equilibria of associating fluids under confinement are investigated using Grand-Canonical Transition Matrix Monte Carlo (GC-TMMC) method. Various properties of coexistence phases and critical properties are estimated for multiple associating fluids at different slit widths. The structural features of coexistence phases are examined through monomer fraction, density profile, and orientation profile. The role of surface sites on the phase behaviour under confinement is critically examined. It has a significant effect on the structural behaviour of coexistence phases, leading to a change in the properties of coexistence phases. In particular, the orientation of associating fluid molecules near the functionalized surface is entirely different than in the case of a smooth surface. The orientation of two sites associating (when sites are located oppositely to each other) fluid molecules is normal to surface, forming bonds with surface sites in one direction and another bond with molecules in an adjacent layer.