Enhancement of microorganism swimming speed in active matter

TL;DR

This paper investigates how activity in an active nematic liquid crystal enhances microorganism swimming speed, showing that activity can significantly increase speed near a critical activity level.

Contribution

It introduces a perturbative approach to analyze swimming in active nematics and reveals a substantial speed increase near the activity threshold.

Findings

Effective shear viscosity decreases with activity, reaching zero at a critical point.

Swimming speed is inversely proportional to the effective shear viscosity.

Numerical simulations show activity can boost swimming speed by an order of magnitude.

Abstract

We study a swimming undulating sheet in the isotropic phase of an active nematic liquid crystal. Activity changes the effective shear viscosity, reducing it to zero at a critical value of activity. Expanding in the sheet amplitude, we find that the correction to the swimming speed due to activity is inversely proportional to the effective shear viscosity. Our perturbative calculation becomes invalid near the critical value of activity; using numerical methods to probe this regime, we find that activity enhances the swimming speed by an order of magnitude compared to the passive case.