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

Vincent Martinez (1) , Eric Clément (2) , Jochen Arlt (1) , Carine C Douarche (3) , Angela Dawson (1) , Jana Schwarz-Linek (1) , Adama Creppy (3) , Viktor Škultéty (1) , Alexander A Morozov (4, 1) , Harold Auradou (3) , Wilson Poon (1)

1 SUPA School of Physics and Astronomy [Edinburgh]
2 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)
3 FAST - Fluides, automatique, systèmes thermiques
4 Edin. - University of Edinburgh

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, ϕc≈0.75%, 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.

Mots clés: particle tracking; rheology and imaging; Escherichia coli; particle image velocimetry; active matter

Domaines: Physique [physics]; Mécanique des fluides [physics.class-ph]

Vincent Martinez, Eric Clément, Jochen Arlt, Carine C Douarche, Angela Dawson, et al.. A combined rheometry and imaging study of viscosity reduction in bacterial suspensions. Proceedings of the National Academy of Sciences of the United States of America, 2020, 117 (5), pp.2326 - 2331. ⟨10.1073/pnas.1912690117⟩. ⟨hal-02487205⟩