CAPILLARY CONDENSATION IN THE LATTICE GAS-MODEL - A MONTE-CARLO STUDY

A three-dimensional lattice gas model with nearest-neighbor attractive interaction confined to a slitlike adsorbing capillary of thickness D is studied by computer simulation, varying the chemical potential mu, temperature, T, as well as the strength of the short-range interaction between the walls of the capillary and the gas. We show that the chemical potential mu(c) (D) at the condensation transition in the capillary is shifted relative to its bulk value mu(c) (infinity) according to the Kelvin equation, mu(c) (D) - mu(c) (infinity) is-proportional-to D-1, for large enough D. Deviations are found for small D, however (of the order of 10 lattice spacings), particularly under conditions where for mu = mu(c) (infinity) the surfaces of the capillary for D --> infinity are wet. For D = 16 lattice spacings we also locate a capillary condensation critical point, and study the distortion of the gas-fluid coexistence curve due to the attractive walls. Profiles of density and local energy across the capillary are studied, and data for the temperature dependence of the local density at the wall both in the gas and in the liquid phase are presented. It is shown that these quantities vary very smoothly near the wetting temperature T(w) of the bulk (D --> infinity) system.