Rheology of Active Polymer-like T. Tubifex Worms

TL;DR

This study investigates the rheological behavior of living Tubifex worms as active polymers, revealing how their activity influences shear-thinning and viscosity, thus opening new avenues in active matter research.

Contribution

It introduces living worms as a novel active polymer system and explores how their activity modifies rheological properties compared to passive polymers.

Findings

Shear thinning is reduced by activity.

Characteristic shear rate relates to activity time scale.

Viscosity scaling differs from regular polymers.

Abstract

Of all complex fluids, it is probably the rheology of polymers we understand best. In-depth insight into the entanglement and reptation of individual polymers allows us to predict for instance the shear-thinning rheology and the behaviour in virtually any flow situation of practical importance. The situation is markedly different when we move from passive to active polymers where the coupling of filament activity, hydrodynamic interactions, and conformations open the way to a plethora of novel structural and dynamical features. Here we experimentally study the rheology of long, slender and entangled living worms (Tubifex tubifex) and propose this system as a new type of active polymer. Its level of activity can be controlled by changing the temperature or by adding small amounts of alcohol to make the worms temporarily inactive. We find that (i) shear thinning is reduced by activity, (ii) the characteristic shear rate for the onset of shear-thinning is given by the time scale of the activity, and (iii) the low shear viscosity as a function of concentration shows a very different scaling from that of regular polymers. Our study paves the way towards a new research field of `living polymers'.