Clustering and phase separation of circle swimmers dispersed in a monolayer

TL;DR

This study uses simulations to explore how circle swimmers in a monolayer behave collectively, revealing how active rotation influences clustering, phase separation, and vortex formation.

Contribution

It introduces a detailed simulation analysis of circle swimmers, highlighting the impact of active rotation on collective behaviors and proposing a gear-like model for vortex formation.

Findings

Active rotation narrows the phase coexistence region.

Clockwise vortices emerge at specific propulsion torques.

A gear-like model explains vortex mechanisms.

Abstract

We perform Brownian dynamics simulations in two dimensions to study the collective behavior of circle swimmers, which are driven by both, an (effective) translational and rotational self-propulsion, and interact via steric repulsion. We find that active rotation generally opposes motility-induced clustering and phase separation, as demonstrated by a narrowing of the coexistence region upon increase of the propulsion angular velocity. Moreover, although the particles are intrinsically assigned to rotate counterclockwise, a novel state of clockwise vortices emerges at an optimal value of the effective propulsion torque. We propose a simple gear-like model to capture the underlying mechanism of the clockwise vortices.