Lamellar ordering, droplet formation and phase inversion in exotic active emulsions

TL;DR

This study numerically explores how active forces influence the formation and morphology of emulsions in mixtures of passive fluids and active gels, revealing activity-dependent phase behaviors and structures.

Contribution

It demonstrates how activity can be used as a control parameter to engineer diverse and exotic emulsion morphologies in active-passive fluid mixtures.

Findings

Moderate activity enhances lamellar ordering.

Strong activity creates passive droplets in active matrices.

Switching activity induces phase inversion.

Abstract

We study numerically the behaviour of a mixture of a passive isotropic fluid and an active polar gel, in the presence of a surfactant favouring emulsification. Focussing on parameters for which the underlying free energy favours the lamellar phase in the passive limit, we show that the interplay between nonequilibrium and thermodynamic forces creates a range of multifarious exotic emulsions. When the active component is contractile (e.g., an actomyosin solution), moderate activity enhances the efficiency of lamellar ordering, whereas strong activity favours the creation of passive droplets within an active matrix. For extensile activity (occurring, e.g., in microtubule-motor suspensions), instead, we observe an emulsion of spontaneously rotating droplets of different size. By tuning the overall composition, we can create high internal phase emulsions, which undergo sudden phase inversion when activity is switched off. Therefore, we find that activity provides a single control parameter to design composite materials with a strikingly rich range of morphologies.