Density functional study of non-isothermal hard sphere fluids

Abstract

ABSTRACT Using a version of dynamical density functional theory, we explore a microscopic structure of hard-sphere fluids in the presence of a temperature gradient. When combined with the assumption of local equilibrium, this approach predicts the density profile in confinement and in bulk both in very good overall agreement with the results from the reverse non-equilibrium molecular dynamics simulation, which we used to impose a temperature gradient. Thus, the assumption of local equilibrium is found to be surprisingly accurate down to a microscopic scale even under a large temperature gradient. An oscillatory density profile, indicating the layering of particles, was observed in bulk as well as in confinement. This behaviour in the latter is well known and results from packing of hard spheres next to a wall. In the former, the oscillation is seen to emanate from the point of sharp change in temperature. However, our theoretical predictions greatly exaggerate the amplitude of oscillation when the temperature exhibits a sharp change over a very small distance.