Dynamics of active liquid interfaces

TL;DR

This paper investigates how mechanical activity influences the behavior of liquid interfaces between active and passive fluids, revealing chaotic flows, active waves, droplet formation, and non-equilibrium wetting transitions, advancing soft active matter control.

Contribution

It introduces experimental and theoretical insights into mechanically driven active interfaces, highlighting phenomena like interfacial fluctuations, droplet generation, and wetting transitions not previously characterized.

Findings

Chaotic flows cause giant interfacial fluctuations.

High activity leads to droplet formation and emulsion states.

Active interfaces can climb walls against gravity.

Abstract

Controlling interfaces of phase separating fluid mixtures is key to creating diverse functional soft materials. Traditionally, this is accomplished with surface-modifying chemical agents. Using experiment and theory, we study how mechanical activity shapes soft interfaces that separate an active and a passive fluid. Chaotic flows in the active fluid give rise to giant interfacial fluctuations and non-inertial propagating active waves. At high activities, stresses disrupt interface continuity and drive droplet generation, producing an emulsion-like active state comprised of finite-sized droplets. When in contact with a solid boundary, active interfaces exhibit non-equilibrium wetting transitions, wherein the fluid climbs the wall against gravity. These results demonstrate the promise of mechanically driven interfaces for creating a new class of soft active matter.