The density profile of a confined fluid

Abstract

The density profile of a liquid confined in a narrow capillary depends markedly on the ratio of capillary radius to molecular size σ. We present a direct comparison of the results of a non-local density functional theory (smoothed density approximation) for the profiles of coexisting ‘liquid’ and ‘gas’ phases of a Lennard-Jones fluid confined in a structureless cylindrical capillary with those of recent computer simulations. Good quantitative agreement is found for capillary radii in the range 3σ to 6σ, indicating that the theory yields an accurate description of packing effects. Taken with earlier results for other problems this suggests that the smoothed density approximation is a versatile theory of inhomogeneous fluids, providing a realistic account of both the phase equilibria and structure of a wide variety of fluid interfaces.