Active Viscoelastic Matter: from Bacterial Drag Reduction to Turbulent Solids

TL;DR

This paper investigates the complex behaviors of active nematic fluids coupled with viscoelastic polymers, revealing enhanced flow dynamics, drag reduction, and the emergence of active turbulence in soft solids.

Contribution

It introduces a coupled model of active nematics and polymer rheology, demonstrating novel flow phenomena and turbulence in active viscoelastic materials.

Findings

Polymer coupling increases flow complexity.

Polymer can reduce flow resistance ('drag reduction').

Active turbulence can occur in soft elastomeric solids.

Abstract

A paradigm for internally driven matter is the active nematic liquid crystal, whereby the equations of a conventional nematic are supplemented by a minimal active stress that violates time reversal symmetry. In practice, active fluids may have not only liquid crystalline but also viscoelastic polymer degrees of freedom. Here we explore the resulting interplay by coupling an active nematic to a minimal model of polymer rheology. We find that adding polymer can greatly increase the complexity of spontaneous flow, but can also have calming effects, thereby increasing the net throughput of spontaneous flow along a pipe (a 'drag-reduction' effect). Remarkably, active turbulence can also arise after switching on activity in a sufficiently soft elastomeric solid.