Activity-induced Nonequilibrium Vaporization Leads to Reentrant Phase Separation

TL;DR

This paper reveals that activity-induced vaporization in active Brownian particles can hinder phase separation, leading to reentrant behavior, and provides a theoretical framework supported by simulations to understand this nonequilibrium phenomenon.

Contribution

The study introduces a kinetic theory explaining how activity-induced vaporization causes reentrant phase separation in active particles, a novel insight into nonequilibrium effects.

Findings

Activity-induced vaporization can prevent dense phase formation at high activity levels.

Reentrant phase separation occurs due to the interplay of effective attraction and vaporization.

Simulations confirm the theoretical predictions about phase behavior dependence on activity and interaction strength.

Abstract

Active Brownian particles (ABPs) with pure repulsion is an ideal model to understand the effect of nonequilibrium on collective behaviors. It has long been established that activity can create effective attractions leading to motility-induced phase separation (MIPS), whose role is similar to that of (inverse) temperature in the simplest equilibrium system with attractive inter-particle interactions. Here, our theoretical analysis based on a kinetic theory of MIPS shows that a new type of activity-induced nonequilibrium vaporization is able to hinder the formation of dense phase when activity is large enough. Such nonequilibrium vaporization along with the activity-induced effective attraction thus lead to a MIPS reentrance. Numerical simulations verify such nonequilibrium effect induced solely by activity on phase behaviors of ABPs, and further demonstrate the dependence of MIPS on activity and the strength of inter-particle interaction predicted by our theoretical analysis. Our findings highlight the unique role played by the nonequilibrium nature of activity on phase behaviors of active systems, which may inspire deep insights into the essential difference between equilibrium and nonequilibrium systems.