Locomotion and transport in a hexatic liquid crystal

TL;DR

This study investigates how hexatic liquid-crystalline order influences the swimming behavior of a model microorganism, revealing that anisotropic fluid properties can significantly alter swimming speed and direction.

Contribution

It provides a theoretical analysis of swimmer dynamics in a hexatic liquid crystal, highlighting the effects of anisotropy and boundary conditions on propulsion.

Findings

Large rotational viscosity can reverse swimming direction.

Anisotropic properties significantly affect power dissipation and flux.

Weak anchoring enhances departure from isotropic behavior.

Abstract

The swimming behavior of bacteria and other microorganisms is sensitive to the physical properties of the fluid in which they swim. Mucus, biofilms, and artificial liquid-crystalline solutions are all examples of fluids with some degree of anisotropy that are also commonly encountered by bacteria. In this article, we study how liquid-crystalline order affects the swimming behavior of a model swimmer. The swimmer is a one-dimensional version of G. I. Taylor's swimming sheet: an infinite line undulating with small-amplitude transverse or longitudinal traveling waves. The fluid is a two-dimensional hexatic liquid-crystalline film. We calculate the power dissipated, swimming speed, and flux of fluid entrained as a function of the swimmer's waveform as well as properties of the hexatic film, such as the rotational and shear viscosity, the Frank elastic constant, and the anchoring strength. The departure from isotropic behavior is greatest for large rotational viscosity and weak anchoring boundary conditions on the orientational order at the swimmer surface. We even find that if the rotational viscosity is large enough, the transverse-wave swimmer moves in the opposite direction relative to a swimmer in an isotropic fluid.