Hydrodynamic stresses in a multi-species suspension of active Janus colloids

TL;DR

This paper investigates how multi-species active Janus colloids influence hydrodynamic stresses in a fluid, revealing how activity types and interactions modify the stress tensor and induce non-reciprocal hydrodynamics.

Contribution

It provides a systematic coarse-grained calculation of the hydrodynamic stress tensor for multi-species active colloids, highlighting the effects of activity and non-reciprocity.

Findings

Stress strength depends on self-propulsion and chemotactic alignment.

Activity can produce contractile or extensile stresses.

Non-reciprocal hydrodynamic interactions emerge in active mixtures.

Abstract

A realistic description of active particles should include interactions with the medium, commonly a momentum-conserving simple fluid, in which they are suspended. In this work, we consider a multi-species suspension of self-diffusiophoretic Janus colloids interacting via chemical and hydrodynamic fields. Through a systematic coarse-graining of the microscopic dynamics, we calculate the multi-component contribution to the hydrodynamic stress tensor of the incompressible Stokesian fluid in which the particles are immersed. For a single species, we find that the strength of the stress produced by the gradients of the number density field is determined by the particles' self-propulsion and chemotactic alignment, and can be tuned to be either contractile or extensile. For a multi-species system, we unveil how different forms of activity modify the stress tensor, and how non-reciprocity in hydrodynamic interactions emerges in an active binary mixture.