Physics / ChBE Guest Seminar

Abstract

We propose a new 'active particle' system in which the particles are in fact polymer-like: the Tubifex tubifex or 'sludge' worm. I will discuss three recent experiments that highlight the richness of this active system. In the first experiment, we perform 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.

In a second experiment, we disperse the worm in a quasi-2D aquarium and observe their spontaneous aggregation to compact, highly entangled blobs; a process similar to polymer phase separation, and for which we observe power-law growth kinetics. We find that the phase separation of active polymer-like worms does not occur through Ostwald ripening, but through active motion and coalescence of the phase domains. Interestingly, the growth mechanism differs from conventional growth by droplet coalescence: the diffusion constant characterizing the random motion of a worm blob is independent of its size, a phenomenon that can be explained from the fact that the active random motion arises only from the worms at the surface of the blob. This leads to a fundamentally different phase-separation mechanism, that may be unique to active polymers. Finally, in the remaining time, I will briefly show that we can efficiently separate by size and activity these living polymers using hydrodynamic chromatography technics.

Bio

Antoine Deblais is an assistant professor at the University of Amsterdam since 2021. Before that, he spent two years as a Postdoctoral researcher at the University of Amsterdam (UvA), Netherlands(2017-2019). He worked on many problems involving flows and instabilities of complex fluids in different situations. With the obtention of an individual Marie-Curie Fellowship, he pursued his independent research between Unilever research centre in Wageningen (Netherlands) and UvA on the relationship between rheology of complex fluids and mouthfeel. He completed his PhD at the University of Bordeaux in France in 2016. His research interests span on the flow of complex fluids, capillarity, and active matter.