# Thermodynamic Approach to the Self-Diffusiophoresis of Colloidal Janus Particles

## TL;DR

This paper introduces a thermodynamic framework for understanding self-diffusiophoresis in colloidal Janus particles, emphasizing entropy production and force asymmetries over traditional concentration gradient models.

## Contribution

It presents a novel thermodynamic approach linking dynamics to entropy production, revisiting propulsion mechanisms in binary solvents and catalytic swimmers.

## Key findings

- Propulsion arises from forces at the poles perpendicular to the surface.
- Asymmetric dissipation drives propulsion, not just solute concentration.
- The approach recovers known results for catalytic swimmers.

## Abstract

Most available theoretical predictions for the self-diffusiophoretic motion of colloidal particles are based on the hydrodynamic thin boundary layer approximation in combination with a solvent body force due to a self-generated local solute gradient. This gradient is enforced through specifying boundary conditions, typically without accounting for the thermodynamic cost to maintain the gradient. Here we present an alternative thermodynamic approach that exploits a direct link between dynamics and entropy production: the local detailed balance condition. We study two cases: First, we revisit self-propulsion in a demixing binary solvent. At variance with a slip velocity, we find that propulsion is due to forces at the poles that are perpendicular to the particle surface. Second, for catalytic swimmers driven through liberating chemical free energy we recover previous expressions. In both cases we argue that propulsion is due to asymmetric dissipation and not simply due to an asymmetric concentration of molecular solutes.