Phase separation in a two-dimensional binary colloidal mixture by quorum sensing activity

TL;DR

This study uses Langevin dynamics simulations to explore how quorum sensing activity induces phase separation and affects glassy behavior in a two-dimensional binary colloidal mixture, revealing distinct regimes of active glass, phase separation, and active liquid.

Contribution

It introduces a novel simulation approach to study quorum sensing activity effects on phase behavior and glassy dynamics in active-passive colloidal mixtures.

Findings

Passive particles form stable phases due to limited momentum transfer from active particles.

Phase separation occurs at intermediate persistence times of active force.

Multiple regimes (active glass, phase separation, active liquid) are identified as persistence time varies.

Abstract

We present results from Langevin dynamics simulations of a glassy active-passive mixture of soft-repulsive binary colloidal disks. Activity on the smaller particles is applied according to the quorum sensing scheme, in which a smaller particle will be active for a persistence time if its local nearest neighbors are equal to or greater than a certain threshold value. We start with a passive glassy state of the system and apply activity to the smaller particles, which shows a nonmonotonous glassy character of the active particles with the persistence time of the active force, from its passive limit (zero activity). On the other hand, passive particles of the active-passive mixture phase separate at the intermediate persistence time of the active force, resulting in the hexatic-liquid and solid-liquid phases. Thus, our system shows three regimes as active glass, phase separation, and active liquid, as the persistence time increases from its smaller values. We show that the solidlike and hexatic phases consisting of passive large particles are stable due to the smaller momentum transfer from active to passive particles, compared to the higher persistence time where the positional and orientational ordering vanishes. Our model is relevant to active biological systems, where glassy dynamics is present, e.g., bacterial cytoplasm, biological tissues, dense quorum sensing bacteria, and synthetic smart amorphous glasses.