Hydrodynamic instabilities in driven chiral suspensions

TL;DR

This paper reveals a new mechanism for chaotic flow in suspensions of torque-driven chiral particles, driven by self-propulsion and coupling of nematic and polar order, distinct from traditional dipolar active matter instabilities.

Contribution

It introduces a novel instability route in chiral suspensions driven by torque monopoles and self-propulsion, expanding understanding of active fluid dynamics.

Findings

Chaotic flows driven by torque monopoles and self-propulsion.

Distinct from dipolar alignment instability.

Coupling between nematic and polar order is key.

Abstract

Active Stokesian suspensions are conventionally understood to generate dipolar stresses that destabilize aligned states in the bulk and drive system-wide spatiotemporally chaotic flows. Here, we report dynamics in suspensions of torque-driven spinning chiral particles that exhibit a distinct and previously unrecognized route to collective dynamics. Using a mean-field kinetic theory, stability analysis, and nonlinear simulations, we demonstrate how flows driven by torque monopoles and self-propulsion resulting from microscopic chirality drive chaotic flows in three dimensions. Unlike the well-known alignment instability of dipolar active matter, the present dynamics is intrinsically tied to self-propulsion and relies on the emergent coupling between nematic and polar order. Our results establish a novel route to pattern formation, suggest strategies for designing torque-driven active suspensions, and provide a mechanistic framework to probe the rheology of chiral fluids.