Structure and Dynamics of a Phase-Separating Active Colloidal Fluid

TL;DR

This study investigates a minimal model of active colloidal fluids composed of self-propelled particles, revealing phase separation, anomalous fluctuations, and a novel active hexatic phase with unique structural and rheological properties.

Contribution

Introduces a minimal model of active colloids showing phase separation and characterizes a new active hexatic phase with unique properties.

Findings

System exhibits phase separation and anomalous fluctuations.

Dense phase identified as an active hexatic with crystalline and viscoelastic features.

Quantified phase diagram and separation kinetics.

Abstract

We examine a minimal model for an active colloidal fluid in the form of self-propelled Brownian hard spheres that interact purely through excluded volume. Despite the absence of an aligning interaction, this system shows the signature behaviors of an active fluid, including anomalous number fluctuations and phase separation behavior. Using simulations and analytic modeling, we quantify the phase diagram and separation kinetics. The dense phase is a unique material that we call an active hexatic, which exhibits the structural signatures of a crystalline solid near the crystal-hexatic transition point, but the rheological and transport properties associated with a viscoelastic fluid.