Velocity alignment promotes motility-induced phase separation

¹ CECAM Centre Européen de Calcul Atomique et Moléculaire, École Polytechnique Fédérale de Lausanne, Batochimie - Avenue Forel 2, 1015 Lausanne, Switzerland
² Departament de Física de la Matèria Condensada, Universitat de Barcelona - Martí i Franqués 1, E-08028 Barcelona, Spain
³ UBICS University of Barcelona Institute of Complex Systems - Martí i Franquès 1, E-08028 Barcelona, Spain

Received: 10 July 2018
Accepted: 2 November 2018

Abstract

We study the phase behavior of polar active Brownian particles moving in two-spatial dimensions and interacting through volume exclusion and velocity alignment. We combine particle-based simulations of the microscopic model with a simple mean-field kinetic model to understand the impact of velocity alignment on the motility-induced phase separation of self-propelled disks. We show that, as the alignment strength is increased, approaching the onset of collective motion from below, orientational correlations grow, rendering the diffusive reorientation dynamics slower. As a consequence, the tendency of particles to aggregate into isotropic clusters is enhanced, favoring the complete de-mixing of the system into a low and high-density phase.