Structural diversity in electrohydrodynamically driven active and organized liquid states

TL;DR

This paper demonstrates that simple biphasic liquids under electrohydrodynamic shear can spontaneously form a wide variety of organized non-equilibrium states, revealing complex pattern formation and active behaviors.

Contribution

It uncovers the diverse range of dissipative organized states emerging in a biphasic system driven by electrohydrodynamic shear, linking phenomena across multiple fields.

Findings

Emergence of 1D corrugation patterns at low shear

Formation of active self-propulsive filaments and networks

Transition to chaotic active emulsions

Abstract

Spontaneous emergence of organized states in materials driven by non-equilibrium conditions is of significant fundamental and technological interest. In many cases, the organized states are complex, hence, with some well-studied exceptions, their emergence is challenging to predict. In this article, we show that an unexpectedly diverse collection of dissipative organized states can emerge in a simple biphasic system consisting of two liquids under planar confinement. We drive the liquid-liquid interface, which is held together by capillary forces, out of thermodynamic equilibrium using DC electrohydrodynamic shearing. As a result, the interface goes through multiple spontaneous symmetry breakings, leading to various organized non-equilibrium states. First, at low shearing, the shear-deformed interface becomes unstable and a 1D quasi-static corrugation pattern emerges. At slightly higher shearing, we observe topological changes that lead to emergence of active self-propulsive fluidic filaments and filament networks, as well as ordered bicontinuous fluidic lattices. Finally, the system transitions into active self-propulsive droplets, quasi-stationary dissipating polygonal and toroidal droplets, and ultimately to a chaotic active emulsion of non-coalescing droplets with complex interactions. Interestingly, this single system captures many features from continuum non-equilibrium pattern formation and discrete active particles, which are often considered separate fields of study. The diversity of observed dissipative organized states is exceptional and points towards many new avenues in the study of electrohydrodynamics, capillary phenomena, non-equilibrium pattern formation, and active materials.