Robust boundary flow in chiral active fluid

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 φ); peak strength appears around a density φ = 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. *

Oscillating collective motion of active rotors in confinement

“…The magnitude of the oscillation decays substantially as r decreases and vanishes far away from the boundary, indicating that the edge flow is localized near the boundary. Previous studies on the confined spinners also reveal the emergence of the edge flow, but with no oscillation (12,32,33).…”

“…Nevertheless, as a representative chiral active matter that breaks both parity and time-reversal symmetries, the active-rotor systems have recently been the subject of fundamental theoretical interest (30,31). It has been reported that a fluid of interacting rotors in confinement yields a collective edge flow parallel to the boundary (12,32,33), which is proven to be even topologically protected (34). In this case, the steric particle-boundary interactions impose a boundary condition that allows the conversion of spin-angular momentum into "orbital" angular momentum.…”

Sorting and Extraction of Self-Propelled Chiral Particles by Polarized Wall Currents

“…A recent development in active matter concerns the use of chiral particles. Two classes of chiral particles may be identified with, first, the spinners [7][8][9][10][11][12][13][14], meaning rotating elements without directional motion, and second, the circling particles [15][16][17][18][19][20][21][22][23][24] combining directional and rotational activity.…”

Exceptional non-Hermitian topological edge mode and its application to active matter

“…Furthermore, we explicitly show the existence of exceptional edge modes in a more realistic system based on active matter 46 , which is a collection of self-propelled particles and has recently attracted much interest as a useful platform to study biological and out-of-equilibrium physics. Recent studies [47][48][49][50][51][52] have explored the existence of the edge modes in active matter protected by the bulk topology. Some of them 49,50,52 have utilized chiral active matter, which moves in a circular path or self-rotates.…”

“…Recent studies [47][48][49][50][51][52] have explored the existence of the edge modes in active matter protected by the bulk topology. Some of them 49,50,52 have utilized chiral active matter, which moves in a circular path or self-rotates. Chiral active matter has been experimentally realized, for example, in bacteria 53 and artificial L-shaped particles 54 .…”