Self-diffusiophoresis of Janus particles that release ions

Abstract

Catalytic Janus swimmers demonstrate a diffusiophoretic 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 the 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.