Self-diffusiophoresis of Janus particles that release ions

TL;DR

This paper develops a theoretical model for Janus particles that release both types of ions, accurately predicting their self-diffusiophoretic motion and explaining phenomena like motion reversal with salt concentration changes.

Contribution

It provides a simple, accurate expression for particle velocity considering both ion types, extending previous models limited to single ion release or low fluxes.

Findings

Derived an expression for particle velocity in the thin diffuse layer limit.

Explained motion reversal phenomena with salt concentration variations.

Predicted self-diffusiophoresis of uncharged particles.

Abstract

Catalytic Janus swimmers demonstrate a diffusio-phoretic motion by self-generating the gradients of concentrations and electric potential. Recent work has focused on simplified cases, such as a release of solely one type of ions or low surface fluxes of ions, with limited theoretical guidance. Here, we consider the experimentally relevant case of particles that release both types of ions, and obtain a simple expression for a particle velocity in the limit of thin electrostatic diffuse layer. Our approximate expression is very accurate even when ion fluxes and surface potentials are large, and allows one to interpret a number of intriguing phenomena, such as the reverse in the direction of the particle motion in response to variations of the salt concentration or self-diffusiophoresis of uncharged particles.