Physics-Biology interface seminar: Aurore Loisy


11:00 - 12:00

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Active fluids under confinement: spontaneous flow and negative viscosity

Aurore Loisy (School of Mathematics, University of Bristol)

Seminar hosted by Harold Auradou

It has been known for a long time that adding motile bacteria to a liquid lowers the viscosity of the mixture. But only recently came the experimental evidence that this phenomenon can continue until a zero viscosity is reached (Lopez, Gachelin, Douarche, Auradou, & Clément, Phys. Rev. Lett. 115, 028301 (2015)). An even more intriguing result in this experiment was the (single) data point located below the zero-viscosity threshold. So, how is it possible to observe a steady state with a negative viscosity? In this talk I will use a simple model of an active liquid and propose an explanation to this peculiar phenomenon.

Time permitting, I will then consider a drop of active liquid (a minimal model for the actomyosin cytoskeleton) and show how the same physics allows this drop to propel itself on a substrate without the need to exert any traction locally on the surface. This mode of self-propulsion, which does not rely on adhesion, may be relevant to cell motility in crowded environments.

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