Bicontinuity in active phase separation

TL;DR

This study investigates how active fluids can create stable, reconfigurable bicontinuous structures through chaotic flows, contrasting with passive phase separation, and highlights the role of activity and surface tension in controlling morphology.

Contribution

It introduces the concept of active bicontinuous structures formed by active phase separation, showing their unique morphology and stability driven by active stresses, unlike passive systems.

Findings

Active flows induce giant interfacial deformations.

Active bicontinuous structures are dominated by sheet-like interfaces.

Activity suppresses coarsening, maintaining steady-state morphologies.

Abstract

We study phase separation between coexisting active and passive fluids in three-dimensions, using numerical simulation and experiments. Chaotic flows of the active phase drive giant interfacial deformations, causing the co-existing phases to interpenetrate and generate a continuously reconfiguring bicontinuous morphology which persists over the lifetime of the active fluid. Active bicontinuous structures are dominated by sheet-like interfaces, in marked difference from passive liquid-liquid phase separation which is controlled by saddle-like surfaces. Activity and surface tension control the length scale of the bicontinuous structure. These results demonstrate how active stresses suppress the coarsening of conventional phase separation, generating steady-state reconfigurable morphologies not accessible with conventional surface-modifying agents or through quenching of transient phase separated structures.