Clustering and pattern formation in chemorepulsive active colloids

TL;DR

This paper explores how chemorepulsion in active colloids leads to clustering and pattern formation, revealing mechanisms that could inform the design of synthetic swimmers and biological systems.

Contribution

It introduces a generic route to clustering via chemorepulsion, highlighting effects of anisotropic chemical production and delayed responses in active colloids.

Findings

Clusters grow linearly with self-propulsion speed.

Chemorepulsion induces a clustering instability.

Results align with observations of dynamic clusters in Janus colloids.

Abstract

We demonstrate that migration away from self-produced chemicals (chemorepulsion) generates a generic route to clustering and pattern formation among self-propelled colloids. The clustering instability can be caused either by anisotropic chemical production, or by a delayed orientational response to changes of the chemical environment. In each case, chemorepulsion creates clusters of a self-limiting area which grows linearly with self-propulsion speed. This agrees with recent observations of dynamic clusters in Janus colloids (albeit not yet known to be chemorepulsive). More generally, our results could inform design principles for the self-assembly of chemorepulsive synthetic swimmers and/or bacteria into nonequilibrium patterns.