Robust boundary flow in chiral active fluid

TL;DR

This study demonstrates that boundary flow in active chiral fluids of self-spinning rotors is robust and topologically protected, influenced by rotor density and boundary shape, and can be modeled with a simple continuum theory.

Contribution

It provides experimental evidence and a continuum model showing boundary flow robustness in active chiral fluids, highlighting topological protection mechanisms.

Findings

Flow strength peaks at rotor density of 0.65

Boundary curvature significantly affects flow strength

A continuum theory with a single parameter accurately reproduces experimental results

Abstract

We perform experiments on an active chiral fluid system of self-spinning rotors in confining boundary. Along the boundary, actively rotating rotors collectively drives a unidirectional material flow. We systematically vary rotor density and boundary shape; boundary flow robustly emerges under all conditions. Flow strength initially increases then decreases with rotor density (quantified by area fraction $\phi$); peak strength appears around a density $\phi=0.65$. Boundary curvature plays an important role: flow near a concave boundary is stronger than that near a flat or convex boundary in the same confinements. Our experimental results in all cases can be reproduced by a continuum theory with single free fitting parameter, which describes the frictional property of the boundary. Our results support the idea that boundary flow in active chiral fluid is topologically protected; such robust flow can be used to develop materials with novel functions.