Fluid behaviour in narrow pores

Abstract

The behaviour of a Lennard-Jones fluid confined within a straight cylindrical pore has been studied using mean-field theory. The fluid potential parameters were chosen to model argon, and a range of wall–fluid parameters, including values approximating carbon dioxide and graphite walls, was investigated. We calculated the density profile and grand potential of the fluid, and examined the effect of varying the pore radius, pressure, temperature, and strength of the wall–fluid forces on these properties, and especially on the gas–liquid phase transitions that occur. We found that the gas–liquid transition occurs at pressures below the bulk fluid vapour pressure in all cases studied. For a fixed temperature, when the pore radius is decreased the gas–liquid coexistence curve ends in a critical point, as has been observed for fluids between parallel plates. The strength of the wall–fluid forces had a dramatic effect on the phase diagram, changing both the range of pore sizes in which phase transitions occur, and the effect of temperature on them.