Dynamics of Motility-Induced clusters: coarsening beyond Ostwald ripening

TL;DR

This paper investigates the complex dynamics of motility-induced clusters in active matter, revealing a novel aggregation mechanism that surpasses traditional Ostwald ripening and results in fractal structures with enhanced mobility.

Contribution

The study introduces a new algorithm for tracking cluster trajectories and uncovers a coarsening process beyond Ostwald ripening in active Brownian disks.

Findings

Active clusters exhibit self-propulsion with diffusivity scaling as Pe^2/√M.

Clusters form large fractal structures with diverse hexatic orders.

Active systems differ significantly from passive counterparts in cluster dynamics.

Abstract

We study the dynamics of clusters of Active Brownian Disks generated by Motility-Induced Phase Separation, by applying an algorithm that we devised to track cluster trajectories. We identify an aggregation mechanism that goes beyond Ostwald ripening but also yields $z=3$. Active clusters of mass $M$ self-propel with enhanced diffusivity $D\sim$ Pe$^2/\sqrt{M}$. Their fast motion drives aggregation into large fractal structures, which are patchworks of diverse hexatic orders, and coexist with regular, orientationally uniform, smaller ones. To bring out the impact of activity, we perform a comparative study of a passive system that evidences major differences with the active case.