Diffusion Transients in Motility-Induced Phase Separation

TL;DR

This study numerically explores how active particles in a two-dimensional suspension undergo motility-induced phase separation, revealing hysteresis in diffusion constants and non-Gaussian displacement distributions during phase transitions.

Contribution

It provides new insights into diffusion behavior and phase transition signatures in active matter systems with motility-induced phase separation.

Findings

Diffusion constant shows hysteresis with sharp jumps at phase boundaries.

Displacement distributions are non-Gaussian with transient tails during phase separation.

No hysteresis observed between dense phase spinodal and binodal, indicating phase overlap.

Abstract

We numerically investigate normal diffusion in a two-dimensional athermal suspension of active particles undergoing motility-induced phase separation. The particles are modeled as achiral Janus disks with fixed self-propulsion speed and weakly fluctuating orientation. When plotted versus the overall suspension packing fraction, the relevant diffusion constant traces a hysteresis loop with sharp jumps in correspondence with the binodal and spinodal of the gaseous phase. No hysteresis loop is observed between the spinodal and binodal of the dense phase, as they appear to overlap. Moreover, even under steady-state phase separation, the particle displacement distributions exhibit non-Gaussian normal diffusion with transient fat (thin) tails in the presence (absence) of phase separation.