Impact of dipole-dipole interactions on motility-induced phase separation

TL;DR

This paper develops a hydrodynamic theory for dipolar active particles that predicts how dipole interactions influence motility-induced phase separation, aligning well with simulations and revealing microscopic mechanisms behind phase destabilization.

Contribution

The paper introduces a hydrodynamic framework for dipolar active particles that accurately predicts the suppression of MIPS due to dipolar interactions, validated by simulations.

Findings

Dipolar interactions hinder MIPS in active Brownian particles.

Hydrodynamic theory quantitatively matches particle simulations.

Microscopic mechanisms of phase destabilization are elucidated.

Abstract

We present a hydrodynamic theory for systems of dipolar active Brownian particles which, in the regime of weak dipolar coupling, predicts the onset of motility-induced phase separation (MIPS), consistent with Brownian dynamics (BD) simulations. The hydrodynamic equations are derived by explicitly coarse-graining the microscopic Langevin dynamics, thus allowing for a quantitative comparison of parameters entering the coarse-grained model and particle-resolved simulations. Performing BD simulations at fixed density, we find that dipolar interactions tend to hinder MIPS, as first reported in [Liao et al., Soft Matter, 2020, 16, 2208]. Here we demonstrate that the theoretical approach indeed captures the suppression of MIPS. Moreover, the analysis of the numerically obtained, angle-dependent correlation functions sheds light into the underlying microscopic mechanisms leading to the destabilization of the homogeneous phase.