Layering and position-dependent diffusive dynamics of confined fluids

TL;DR

This study investigates how confinement affects the diffusion of hard-sphere fluids, revealing that local density and available volume influence diffusivity, with local and global diffusivities linked through a master curve.

Contribution

It provides new insights into position-dependent diffusion in confined fluids and establishes a relationship between local packing, volume, and diffusivity.

Findings

Normal diffusion coefficient varies with position and density.

Local and global diffusivities follow a master curve when scaled.

Diffusivity deviates from bulk behavior under confinement.

Abstract

We study the diffusive dynamics of a hard-sphere fluid confined between parallel smooth hard walls. The position-dependent diffusion coefficient normal to the walls is larger in regions of high local packing density. High density regions also have the largest available volume, consistent with the fast local diffusivity. Indeed, local and global diffusivities as a function of the Widom insertion probability approximately collapse onto a master curve. Parallel and average normal diffusivities are strongly coupled at high densities and deviate from bulk fluid behavior.