# Hydrodynamics defines the stable swimming direction of spherical squirmers in a nematic liquid crystal

## TL;DR

This study investigates how hydrodynamic interactions influence the orientation of spherical squirmers in nematic liquid crystals, revealing that swimmer type determines alignment with the nematic director.

## Contribution

It combines simulations and analytic calculations to show that hydrodynamic coupling causes specific orientation behaviors of squirmers in nematic environments, a novel insight.

## Key findings

- Pushers swim parallel to the nematic director.
- Pullers swim perpendicular to the nematic director.
- Hydrodynamic coupling drives orientation based on swimmer type.

## Abstract

We present a study of the hydrodynamics of an active particle, a model squirmer, in an envi- ronment with a broken rotational symmetry: a nematic liquid crystal. By combining simulations with analytic calculations, we show that the hydrodynamic coupling between the squirmer flow field and liquid crystalline director can lead to re-orientation of the swimmers. The preferred orientation depends on the exact details of the squirmer flow field. In a steady state, pushers are shown to swim parallel with the nematic director while pullers swim perpendicular to the nematic director. This behaviour arises solely from hydrodynamic coupling between the squirmer flow field and anisotropic viscosities of the host fluid. Our results suggest that an anisotropic swimming medium can be used to characterise and guide spherical microswimmers in the bulk.