Using Activity to Compartmentalize Binary Mixtures

TL;DR

This study investigates how mixtures of active particles with different speeds behave at steady state, revealing unique phase behaviors and fluctuations driven by their activity ratios, with implications for various complex systems.

Contribution

We introduce a computational framework to analyze binary mixtures of active particles with varying activity ratios, uncovering new emergent behaviors and physical mechanisms.

Findings

Non-monotonic macroscopic properties with activity ratio

Microphase separation of particle domains

Enhanced fluctuations and avalanche events

Abstract

We computationally study suspensions of slow and fast active Brownian particles that have undergone motility induced phase separation and are at steady state. Such mixtures, of varying non-zero activity, remain largely unexplored even though they are relevant for a plethora of systems and applications ranging from cellular biophysics to drone swarms. Our mixtures are modulated by their activity ratios ($\mathrm{Pe}^\mathrm{R}$), which we find to encode information by giving rise to three regimes, each of which display their unique emergent behaviors. Specifically, we found non-monotonic behavior of macroscopic properties, e.g. density and pressure, as a function of activity ratio, microphase separation of fast and slow particle domains, increased fluctuations on the interface and severe avalanche events compared to monodisperse active systems. Our approach of simultaneously varying the two activities of the particle species allowed us to discover these behaviors and explain the microscopic physical mechanisms that drive them.