Asymmetric fluctuations and self-folding of active interfaces

TL;DR

This paper investigates how active stresses in microtubule-based fluids cause asymmetric interface fluctuations, leading to self-folding and foam-like phases, combining experiments, simulations, and theory.

Contribution

It reveals the mechanisms behind asymmetric fluctuations and self-folding in active interfaces, highlighting the role of activity in interface dynamics and structure.

Findings

Active flows induce asymmetric interfacial fluctuations.

High activity causes the interface to self-fold and form foam-like phases.

Active stresses control the breakup and reconfiguration of the interface.

Abstract

We study the structure and dynamics of the interface separating a passive fluid from a microtubule-based active fluid. Turbulent-like active flows power giant interfacial fluctuations, which exhibit pronounced asymmetry between regions of positive and negative curvature. Experiments, numerical simulations, and theoretical arguments reveal how the interface breaks up the spatial symmetry of the fundamental bend instability to generate local vortical flows that lead to asymmetric interface fluctuations. The magnitude of interface deformations increases with activity: In the high activity limit, the interface self-folds invaginating passive droplets and generating a foam-like phase, where active fluid is perforated with passive droplets. These results demonstrate how active stresses control the structure, dynamics, and break-up of soft, deformable, and reconfigurable liquid-liquid interfaces.