Phase transitions of adsorbed fluids computed from multiple-histogram reweighting

Abstract

This paper demonstrates the effectiveness of using multiple-histogram reweighting (MHR) to study phase transitions in confined fluids by examining capillary condensation, prewetting, and layering transitions for different systems. A comparison is made with previously published simulations, where available, to establish the accuracy of MHR as applied to inhomogeneous systems. Overlap between adjacent state points is assessed through single-histogram reweighting. Capillary condensation for methane adsorption in slit-like graphite pores exhibits 2D behaviour. Crossover of the effective exponent for the width of the coexistence curve from 2D Ising-like (1/8) further away from the critical point to mean-field (1/2) near the critical point is observed. The reduced critical temperature, the density and the effective value of the exponent for the model system are 0.77, 0.482, and 0.119, respectively, based on a fit to the simulation data. Prewetting transitions are observed for adsorption of Ar on solid CO₂ using model potentials. The wetting temperature is estimated based on the intersection of the pre-wetting and bulk vapour-liquid lines, and also by extrapolation to zero of the difference between the saturation and prewetting chemical potentials. The reduced wetting temperature is estimated to be around 0.69. The reduced prewetting critical temperature, calculated from the disappearance of the two peaks in the density probability distribution, is estimated to be 0.92. The monolayer to bilayer (1-2) transition for propane on graphite is computed over a range of temperatures. Results for the 1–2 layering transition computed from MHR from a small system are in good agreement with grand canonical Monte Carlo simulations for a much larger system.