A combined rheometry and imaging study of viscosity reduction in bacterial suspensions
Vincent A. Martinez, Éric Clément, Jochen Arlt, Carine Douarche, Angela Dawson, Jana Schwarz‐Linek, Adama Creppy, Viktor Škultéty, Alexander N. Morozov, Harold Auradou, Wilson C. K. Poon
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.