Dynamic clustering in active colloidal suspensions with chemical signaling

TL;DR

This study experimentally investigates the phase behavior of dense active colloidal suspensions, revealing a novel cluster phase driven by chemotactic aggregation due to chemical signaling, with cluster size increasing linearly with activity.

Contribution

It demonstrates that chemotactic aggregation explains the observed cluster phase in active colloids, extending understanding of phase behavior in active matter systems.

Findings

Identification of a novel cluster phase at intermediate densities.

Cluster size grows linearly with self-propelling velocity.

Chemotactic aggregation explains the phase behavior.

Abstract

In this paper, we explore experimentally the phase behavior of a dense active suspension of self- propelled colloids. In addition to a solid-like and a gas-like phase observed for high and low densities, a novel cluster phase is reported at intermediate densities. This takes the form of a stationary assembly of dense aggregates, with an average size which grows with activity as a linear function of the self-propelling velocity. While different possible scenarii can be considered to account for these observations - such as a generic velocity weakening instability recently put forward -, we show that the experimental results are reproduced by a chemotactic aggregation mechanism, originally introduced to account for bacterial aggregation, and accounting here for diffusiophoretic chemical interaction between colloidal swimmers.