Dynamic clustering of passive colloids in dense suspensions of motile bacteria

TL;DR

This paper investigates a novel dynamic clustering phase in mixtures of passive colloids and motile bacteria, revealing how active motion and alignment torques lead to phase behavior in dense suspensions.

Contribution

It introduces the concept of a dynamic clustering phase driven by a balance of active motion and alignment torques in colloid-bacteria mixtures.

Findings

Clustering results from a balance between bond breaking and stabilization.

Dynamic clustering occurs over a broad regime of motility parameters.

The phase spans from diffusivity-based to motility-induced phase separation.

Abstract

Mixtures of active and passive particles are predicted to exhibit a variety of nonequilibrium phases. Here we report a dynamic clustering phase in mixtures of colloids and motile bacteria. We show that colloidal clustering results from a balance between bond breaking due to persistent active motion and bond stabilization due to torques that align active particle velocity tangentially to the passive particle surface. Furthermore, dynamic clustering spans a broad regime between diffusivity-based and motility-induced phase separation that subsumes typical bacterial motility parameters.