Shear-induced bimodality and stability analysis of chiral spheroidal swimmers

TL;DR

This study investigates how shear flow influences the behavior and stability of chiral and nonchiral spheroidal swimmers in a channel, revealing mechanisms for flow-driven separation based on chirality and shape.

Contribution

It introduces a comprehensive probabilistic and stability analysis of active spheroidal swimmers under shear flow, highlighting the effects of chirality and shape on their dynamics.

Findings

Shear and chirality induce distinct swimmer accumulation patterns.

Prolate and oblate swimmers exhibit different shear-trapping behaviors.

Results suggest potential for flow-based separation of active particles.

Abstract

We study the shear-induced behavior of chiral (circle-swimming) and nonchiral swimmers in a planar channel subjected to Poiseuille (pressure-driven) flow. The swimmers are modeled as active Brownian spheroids, self-propelling with a fixed-magnitude velocity, pointing along their axis of symmetry. We consider both cases of prolate and oblate swimmers and focus primarily on swimmers that possess an intrinsic, or active, counterclockwise angular velocity, in addition to the shear-induced angular velocity they acquire within the channel flow (Jeffery orbits). The probabilistic results are established using a Smoluchowski equation within the position orientation phase space that is solved numerically. We show that the interplay between shear- and chirality-induced angular velocities, combined with the effects due to particle self-propulsion and steric particle-wall interactions, lead to an interesting range of effects, including pinning, off-centered and near-wall accumulation of swimmers within the channel. This is further accompanied by the linear stability analysis of swimmers, used to explain the probabilistic results. We discuss the qualitative differences of probabilistic results that emerge due to the different regimes of rotational dynamics of swimmers in channel flow, particularly the shear-trapping/-escaping of prolate/oblate swimmers and the difference in latitudes of fixed points associated with each swimmer shape. Our results point to possible mechanisms for flow-driven separation of active spheroidal particles based on their chirality strength.