A combined rheometry and imaging study of viscosity reduction in bacterial suspensions.

Martinez, Vincent A; Clément, Eric; Arlt, Jochen; Douarche, Carine; Dawson, Angela; Schwarz-Linek, Jana; Creppy, Adama K; Škultéty, Viktor et al. · Proc Natl Acad Sci U S A · 2020

basic_science · Level V

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Abstract

Suspending self-propelled "pushers" in a liquid lowers its viscosity. We study how this phenomenon depends on system size in bacterial suspensions using bulk rheometry and particle-tracking rheoimaging. Above the critical bacterial volume fraction needed to decrease the viscosity to zero, [Formula: see text], large-scale collective motion emerges in the quiescent state, and the flow becomes nonlinear. We confirm a theoretical prediction that such instability should be suppressed by confinement. Our results also show that a recent application of active liquid-crystal theory to such systems is untenable.

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