Rheology of Entangled Active Polymer-Like T. Tubifex Worm

We propose a new 'active particle' system in which the particles are in fact polymer-like. We experimentally study the rheology of long, slender, and entangled living worms (Tubifex Tubifex, or 'sludge worms'). Performing classical rheology experiments on this entangled polymer-like system, we find that the rheology is qualitatively similar to that of usual polymers, but, quantitatively, (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. The level of activity can be controlled by changing the temperature but also by adding small amounts of alcohol to make the worms temporarily inactive.