EFFECT OF NANO- CONFINEMENT ON MOLECULAR MOTION OF FLUID

Theoretical results for the flow of fluid through a nano-channel with non-interacting walls are presented. Anisotropy in diffusion, arising due to the presence of walls has been studied by deriving fourth order sum rules of the velocity auto correlation function in direction perpendicular and parallel to walls. The effect of walls has been included by using a dynamical model that considers effect on the molecular motion only. It is shown that the local diffusion normal to the walls gets considerably reduced in the region adjacent to the walls. It has been found that when the width of the channel is of the order of twenty times of the atomic diameter, even the macroscopic diffusion coefficient is reduced due to the presence of walls. On the other hand, shear viscosity of the fluid is enhanced appreciably near the walls. These two transport coefficients approach their bulk values as the channel width increases, although the layers near the walls always have different behavior due to the effect of confmement of the molecular motion. The study finds importance in fundamental understanding of the flow of liquid in a narrow channel. As an example of its application, the relevance to the flow of blood in arteries has been discussed.