Diffusion of spherical particles in microcavities

TL;DR

This paper investigates how confinement within a small cylindrical cavity affects the diffusion of spherical particles, revealing reduced and anisotropic diffusion due to hydrodynamic wall interactions, supported by simulations and a simple predictive model.

Contribution

It provides a detailed analysis of particle diffusion in confined geometries, including a new model that matches simulation results for specific microcavity dimensions.

Findings

Diffusion is reduced compared to bulk fluid

Diffusion becomes anisotropic near walls

A simple model accurately predicts diffusion behavior

Abstract

The diffusive motion of a colloidal particle trapped inside a small cavity filled with fluid is reduced by hydrodynamic interactions with the confining walls. In this work, we study these wall effects on a spherical particle entrapped in a closed cylinder. We calculate the diffusion coefficient along the radial, azimuthal and axial direction for different particle positions. At all locations the diffusion is smaller than in a bulk fluid and it becomes anisotropic near the container's walls. We present a simple model which reasonably well desribes the simulation results for the given dimensions of the cylinder, which are taken from recent experimental work.