Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Focus: Rheology I (joint focus with DRG)

CPP 35.2: Vortrag

Donnerstag, 29. März 2012, 15:30–15:45, C 243

Active viscosity of bacterial suspensions — •Anke Lindner, Jeremie Gachelin, Helene Berthet, Annie Rousselet, Gaston Mino, and Eric Clement — PMMH-ESPCI, 10, rue Vauquelin, 75231 Paris Cedex 05, France

Active suspensions are fluids laden with self-swimming entities such as bacteria, algae or artificial swimmers. The self-propelled particles inject energy into the suspending fluid, leading to very different properties of active compared to passive suspensions. In particular, it has been predicted theoretically that the viscosity of suspensions of so called pushers can be reduced compared to the viscosity of the suspending fluid.

Pioneering experimental measurements have confirmed that finding, but no bulk rheological experiments at controlled shear rates exist up to date. Here we present experiments measuring the viscosity of a wild type E-Coli suspension. To this purpose, we use a Y shaped micro-fluidic channel as a rheometer allowing us to resolve small differences between the viscosity of the suspending fluid and the active suspension at low shear rates and with a high resolution. We systematically vary the shear rate and the bacterial density. In this way we show that in a specific range of parameters the viscosity of the active suspension is lower than the viscosity of the suspending fluid. We discuss our results in the perspective of recent theoretical and experimental works .