Dynamical clustering and phase separation in suspensions of self-propelled colloidal particles

TL;DR

This study combines experiments and simulations to explore how self-propelled colloidal particles undergo clustering and phase separation, revealing a dynamical instability driven by self-trapping mechanisms.

Contribution

It provides new experimental and simulation evidence of phase separation in self-propelled colloids without alignment interactions, highlighting a dynamical instability mechanism.

Findings

Small clusters stabilized at low densities.

Phase separation into large clusters and dilute gas at higher densities.

Behavior explained by a self-trapping dynamical instability.

Abstract

We study experimentally and numerically a (quasi) two dimensional colloidal suspension of self-propelled spherical particles. The particles are carbon-coated Janus particles, which are propelled due to diffusiophoresis in a near-critical water-lutidine mixture. At low densities, we find that the driving stabilizes small clusters. At higher densities, the suspension undergoes a phase separation into large clusters and a dilute gas phase. The same qualitative behavior is observed in simulations of a minimal model for repulsive self-propelled particles lacking any alignment interactions. The observed behavior is rationalized in terms of a dynamical instability due to the self-trapping of self-propelled particles.