Kinetics of motility-induced phase separation and swim pressure

TL;DR

This paper investigates the pressure behavior of active Brownian particles in two dimensions, revealing a nonmonotonic pressure response linked to phase separation dynamics and identifying distinct kinetic regimes.

Contribution

It provides a detailed analysis of pressure evolution and phase separation kinetics in active matter, highlighting the nonmonotonic pressure behavior as a robust feature.

Findings

Pressure exhibits nonmonotonic behavior with density.

Two dynamical regimes identified during phase separation.

Pressure overshoot is a distinctive feature of active systems.

Abstract

Active Brownian particles (ABPs) represent a minimal model of active matter consisting of self-propelled spheres with purely repulsive interactions and rotational noise. Here, we examine the pressure of ABPs in two dimensions in both closed boxes and systems with periodic boundary conditions and show that its nonmonotonic behavior with density is a robust feature, independent of system size. We correlate the time evolution of the mean pressure towards its steady state value with the kinetics of motility-induced phase separation. For parameter values corresponding to phase separated steady states, we identify two dynamical regimes. The pressure grows monotonically in time during the initial regime of rapid cluster formation, overshooting its steady state value and then quickly relaxing to it, and remains constant during the subsequent slower period of cluster coalescence and coarsening. The overshoot is a distinctive feature of active systems.