Synthetic Quorum Sensing and Absorbing Phase Transitions in Colloidal Active Matter

TL;DR

This paper introduces colloidal active rods capable of quorum sensing, revealing how density-dependent motility regulation induces phase transitions and heterogeneous pattern formation in active matter systems.

Contribution

The study demonstrates for the first time how quorum sensing in synthetic colloids influences phase behavior and pattern formation, combining experiments, simulations, and theory.

Findings

Quorum sensing induces an absorbing phase transition where particles freeze.

Density-dependent motility leads to atypical phase separation with flat interfaces.

Heterogeneous patterns emerge from the competition between quorum sensing and mechanical interactions.

Abstract

Unlike biological active matter that constantly adapt to their environment, the motors of synthetic active particles are typically agnostic to their surroundings and merely operate at constant force. Here, we design colloidal active rods capable of modulating their inner activity in response to crowding, thereby enforcing a primitive form of quorum sensing interactions. Through experiments, simulations, and theory we elucidate the impact of these interactions on the phase behavior of isotropic active matter. We demonstrate that, when conditioned to density, motility regulation can either lead to an absorbing phase transition, where all particles freeze their dynamics, or to atypical phase separation, where flat interfaces supporting a net pressure drop are in mechanical equilibrium. Fully active and fully arrested particles can then form heterogeneous patterns ruled by the competition between quorum sensing and mechanical interactions. Beyond the specifics of motile colloids, we expect our findings to apply broadly to adaptive active matter assembled from living or synthetic units.