Hydrodynamic suppression of phase separation in active suspensions

TL;DR

This study demonstrates through simulations that hydrodynamic interactions significantly suppress motility-induced phase separation in active suspensions of squirming disks, contrasting with previous findings in active Brownian particles.

Contribution

It provides the first detailed numerical evidence that hydrodynamics can suppress phase separation in active matter, challenging prior assumptions about its universality.

Findings

Hydrodynamic interactions strongly suppress MIPS in active suspensions.

Simulations show differences between hydrodynamic and active Brownian particle behaviors.

Hydrodynamics alter the phase behavior of active disks across various densities.

Abstract

We simulate with hydrodynamics a suspension of active disks squirming through a Newtonian fluid. We explore numerically the full range of squirmer area fractions from dilute to close packed and show that "motility induced phase separation" (MIPS), which was recently proposed to arise generically in active matter, and which has been seen in simulations of active Brownian disks, is strongly suppressed by hydrodynamic interactions. We give an argument for why this should be the case and support it with counterpart simulations of active Brownian disks in a parameter regime that provides a closer counterpart to hydrodynamic suspensions than in previous studies.