Active Brownian particles driven by constant affinity

TL;DR

This paper develops a thermodynamically consistent model for active Brownian particles driven by a constant chemical affinity, resulting in variable propulsion speeds linked to potential energy, and captures entropy production without non-conservative forces.

Contribution

It introduces a novel modeling framework for active particles driven by a fixed chemical potential difference, extending standard models by incorporating energy-dependent propulsion speeds.

Findings

Derivation of equations of motion with constant chemical affinity

Demonstration of non-constant propulsion speed depending on potential energy

Modeling of entropy production without non-conservative forces

Abstract

Experimental realizations of self-propelled colloidal Janus particles exploit the conversion of free energy into directed motion. One route are phoretic mechanisms that can be modeled schematically as the interconversion of two chemical species. Here we consider the situation when the difference of chemical potential between the two species (the driving affinity) can be assumed to be constant, and we derive the thermodynamically consistent equations of motion. In contrast to the standard model of active Brownian particles parametrized by a constant self-propulsion speed, this yields a non-constant speed that depends on the potential energy of the suspension. This approach allows to consistently model the breaking of detailed balance and the accompanying entropy production without non-conservative forces.