Inertial Effects on Kinetics of Motility-Induced Phase Separation

TL;DR

This study reveals that inertia significantly alters the kinetics of motility-induced phase separation, changing the phase transition nature and cluster formation process, even at very low inertia levels.

Contribution

It demonstrates how inertia transforms MIPS from a continuous to a discontinuous transition and introduces a nucleation-like clustering process, expanding understanding of active system dynamics.

Findings

Phase transition becomes discontinuous with inertia.

Cluster formation shifts from spinodal decomposition to nucleation-like process.

Discontinuity persists even at very low inertia ratios.

Abstract

Motility-induced phase separation (MIPS) is of great importance and has been extensively researched in overdamped systems, nevertheless, what impacts inertia will bring on kinetics of MIPS is lack of investigation. Here, we find that, not only the phase transition changes from continuous to discontinuous, but also the formation of clusters exhibits a nucleation-like process without any coarsening regime, different from spinodal decomposition in the overdamped case. This remarkable kinetics stems from a competition between activity-induced accumulation of particles and inertia-induced suppression of clustering process. More interestingly, the discontinuity of MIPS still exists even when the ratio of particle mass to the friction coefficient reduces to be very small such as 0.0001. Our findings emphasize the importance of inertia in kinetics of MIPS, and may open a new perspective on understanding the nature of MIPS in active systems.