Viscotaxis of chiral microswimmer in viscosity gradients

TL;DR

This paper investigates how chiral microswimmers navigate viscosity gradients, revealing their tendency to follow spiral paths due to their orientation dynamics modeled by spin system equations, with implications for understanding microscale navigation.

Contribution

It introduces a novel application of Landau-Lifshitz-Gilbert equations to describe microswimmer orientation in viscosity gradients and uncovers the negative viscotaxis behavior of chiral squirmers.

Findings

Chiral squirmers exhibit negative viscotaxis, moving along spiral trajectories.

Misaligned dipoles induce steady-state spiral motion.

Orientation dynamics can be modeled using spin system equations.

Abstract

Microswimmers display an intriguing ability to navigate through fluids with spatially varying viscosity, a behavior known as viscotaxis, which plays a crucial role in guiding their motion. In this study, we reveal that the orientation dynamics of chiral squirmers in fluids with uniform viscosity gradients can be elegantly captured using the Landau-Lifshitz-Gilbert equations, originally developed for spin systems. Remarkably, we discover that chiral swimmers demonstrate negative viscotaxis, tracing spiral trajectories as they move. Specifically, a chiral squirmer with a misaligned source dipole and rotlet dipole exhibits a steady-state spiral motion-a stark contrast to the linear behavior observed when the dipoles are aligned. This work provides fresh insights into the intricate interplay between microswimmer dynamics and fluid properties.