Dynamical Clustering and Phase Separation in Suspensions of Self-Propelled Colloidal Particles

TLDR

The study investigates the behavior of a quasi‑two‑dimensional suspension of self‑propelled spherical colloidal particles through experiments and simulations. The particles are carbon‑coated Janus spheres propelled by diffusiophoresis in a near‑critical water‑lutidine mixture, and the observed behavior is explained as a dynamical instability arising from self‑trapping of the particles. At low densities the propulsion stabilizes small clusters, whereas at higher densities the system phase‑separates into large clusters and a dilute gas, a behavior also reproduced by a minimal model of repulsive self‑propelled particles without alignment.

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.