PHASE TRANSITIONS IN NARROW PORES: THERMODYNAMICS, STATISTICAL MECHANICS, AND COMPUTER SIMULATION

The methods of thermodynamics, density functional theory, and grand canonical Monte Carlo computer simulation were used to study capillary condensation in a model of a narrow cylindrical pore. The predictions of the thermodynamic Kelvin equation were tested with the results of the theories and the simulations.;The simulations produce the structure of the confined fluid and gas-like and liquid-like phases were found. The transition between these two phases was determined by thermodynamic integrations. The transition was found to differ significantly from the Kelvin equation result for pores as wide as fifteen molecular diameters. Two versions of the density functional theory were also tested. The local density approximation gave only qualitative correspondence with the simulations for the phase behavior of the confined fluid and missed the local structure details produced by the simulation. The structure produced by the smoothed density approximation was in much better agreement with the simulations and the overall phase behavior was in semi-quantitative agreement.