Brownian motion of a charged colloid in restricted confinement

TL;DR

This study investigates how electrostatic interactions and hydrodynamic forces influence the Brownian motion of a charged colloid confined between charged walls, revealing how ionic strength controls diffusion behavior.

Contribution

It provides a detailed analysis of the combined electrostatic and hydrodynamic effects on colloid diffusion in confined geometries, introducing a controllable parameter affecting motion.

Findings

Diffusion coefficient follows a sigmoid curve with respect to the dimensionless parameter.

Low ionic strength leads to faster, localized colloid motion.

High ionic strength results in slower movement with wider exploration.

Abstract

We study the Brownian motion of a charged colloid, confined between two charged walls, for small separation between the colloid and the walls. The system is embedded in an ionic solution. The combined effect of electrostatic repulsion and reduced diffusion due to hydrodynamic forces results in a specific motion in the direction perpendicular to the confining walls. The apparent diffusion coefficient at short times as well as the diffusion characteristic time are shown to follow a sigmoid curve as function of a dimensionless parameter. This parameter depends on the electrostatic properties and can be controlled by tuning the solution ionic strength. At low ionic strength, the colloid moves faster and is localized, while at high ionic strength it moves slower and explores a wider region between the walls, resulting in a larger diffusion characteristic time.