Adsorption and capillary condensation of fluids in cylindrical pores by Monte Carlo simulation in the Gibbs ensemble

A recently proposed technique [1] for the direct determination of phase coexistence properties of fluids by simulation was extended for the prediction of adsorption and capillary condensation of simple fluids in narrow cylindrical pores. Two variations of the technique were developed, the first for equilibrium between a bulk fluid phase and the interior of a pore, and the second for the determination of capillary condensation points. The metholology was applied for the calculation of equilibria for the pure Lennard-Jones (6, 12) fluid in a structureless cylindrical pore that interacts with the fluid via an integrated Lennard-Jones potential. The potential parameters were chosen to approximate fluid Ar in a pore of solid CO₂. The phase diagram of the fluid was determined as a function of temperature and pore radius. The gas/liquid critical temperature decreases as the pore radius is reduced. The results from the proposed technique were found to be in good agreement with recent results from independent molecular dynamics calculations. The new method, however, has significant advantages in terms of speed over previously available techniques.