Non-equilibrium pathways between cluster morphologies in active phase separation: necking, rupture and cavitation

TL;DR

This paper explores the non-equilibrium pathways of phase transitions in active matter, revealing how morphology changes depend on fluctuations and Peclet number, with implications for understanding active systems.

Contribution

It uncovers the mechanisms of morphological transitions in active phase separation, highlighting the role of non-equilibrium fluctuations and the suppression of equilibrium pathways at high Peclet numbers.

Findings

Droplet-to-slab transition follows equilibrium-like mechanism.

Slab-to-droplet transition depends on rare fluctuations.

High Peclet numbers suppress equilibrium pathways, favoring bubble mechanisms.

Abstract

We investigate the dynamical pathways of a geometric phase transition in a two-dimensional active lattice gas undergoing motility-induced phase separation. The transition is between metastable morphologies of the liquid cluster: a system-spanning "slab" and a compact "droplet". We generate trajectories of this transition in both directions using forward flux sampling. We find that the droplet-to-slab transition always follows a similar mechanism to its equilibrium counterpart, but the reverse (slab-to-droplet) transition depends on rare non-equilibrium fluctuations. At low Peclet numbers the equilibrium and non-equilibrium pathways compete, while at high Peclet numbers the equilibrium pathway is entirely suppressed, and the only allowed mechanism involves a large vapour bubble. We discuss the implications of these findings for active matter systems more generally.