# Active particles in viscosity gradients

## TL;DR

This paper develops a theoretical framework for understanding how active particles, modeled as squirmers, behave in viscosity gradients, revealing mechanisms for control and sorting based on swimming style.

## Contribution

It introduces a model for active particles in viscosity gradients, demonstrating viscotaxis and proposing a method to control and sort microswimmers by their gait.

## Key findings

- Viscotaxis occurs in squirmers due to viscosity gradients.
- The swimming gait influences how particles respond to viscosity changes.
- Viscosity gradients can be used to control and sort active particles.

## Abstract

Microswimmers in nature often experience spatial gradients of viscosity. In this work we develop theoretical results for the dynamics of active particles, biological or otherwise, swimming through viscosity gradients. We model the active particles using the squirmer model, and show how viscosity gradients lead to viscotaxis for squirmers, and how the effects of viscosity gradients depend on the swimming gait of the microswimmers. We also show how such gradients in viscosity can be used to control active particles and suggest a mechanism to sort them based on their swimming style.