Dynamical clustering and wetting phenomena in inertial active matter

TL;DR

This paper investigates how inertia influences clustering and wetting behaviors in active matter, revealing new phenomena such as phase transitions and boundary effects in macroscopic inertial active particles.

Contribution

It presents experimental evidence on inertial effects in active granular particles, highlighting phenomena absent in overdamped microswimmers.

Findings

Inertia causes a transition from liquid-like to crystal-like cluster structures.

Inertia suppresses boundary nucleation and wetting phenomena.

Inertial active particles do not favor boundary clustering, unlike microswimmers.

Abstract

Dynamical clustering represents a characteristic feature of active matter consisting of self-propelled agents that convert energy from the environment into mechanical motion. At the micron scale, typical of overdamped dynamics, particles with opposite motility block each other and show transient dynamical arrest that can induce cluster nucleation and motility-induced phase separation. However, for macroscopic agents, inertia plays a leading role, and clustering is strongly affected by bounce-back effects during collisions that could inhibit cluster growth. Here we present an experiment on the clustering of active granular particles, in which inertia can be systematically tuned. A plethora of new phenomena impacted severely by inertia is presented. Clusters display an inertia-induced transition from liquid-like to crystal-like inner structures that is accompanied by the suppression of cluster nucleation at system boundaries due to particle inertia. In contrast to microswimmers, where active particles wet the boundary by primarily forming clusters attached to the container walls, in an underdamped inertial active system, walls do not favor cluster formation and effectively annihilate motility-induced wetting phenomena.