Dewetting and Spreading Transitions for Active Matter on Random Pinning Substrates

TL;DR

This paper investigates how active particles interact with random substrates, revealing various phase transitions including wetting, clustering, and pinning, depending on activity, density, and substrate strength.

Contribution

It introduces a comprehensive phase diagram for active matter on disordered substrates, identifying new transitions and phases not previously characterized.

Findings

Identification of a wetting transition in active matter systems

Mapping of phase boundaries as a function of activity and substrate strength

Discovery of coexistence and pinned liquid phases

Abstract

We show that sterically interacting self-propelled disks in the presence of random pinning substrates exhibit transitions among a variety of different states. In particular, from a phase separated cluster state, the disks can spread out and homogeneously cover the substrate in what can be viewed as an example of an active matter wetting transition. We map the location of this transition as a function of activity, disk density, and substrate strength, and we also identify other phases including a cluster state, coexistence between a cluster and a labyrinth wetted phase, and a pinned liquid. These phases can be identified using the cluster size, which dips at the wetting-dewetting transition, and the fraction of sixfold coordinated particles, which drops when dewetting occurs.