Static and dynamic effects of confinement on self-diffusion

Abstract

Expressions for second and fourth sum rules of velocity autocorrelation function have been derived for fluid confined to a rectangular nanotube. Expressions obtained for these sum rules involve density profiles which vary with distance from walls of the tube. These sum rules, incorporating the effect of static changes made due to confinement, and the model which involves dynamical effect have been coupled to study the self-diffusion coefficient. By considering model density profiles, it is found that the self-diffusion coefficient in a direction perpendicular to the wall behaves differently from that in a direction parallel to the wall. The perpendicular diffusion coefficient is found to be more strongly dependent on the width of the tube than the parallel diffusion. It is found that dynamical effects are more in the region that is near to the confining wall than the static effects which track density profile.