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

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Original languageEnglish
Article number201912690
JournalProceedings of the National Academy of Sciences of the United States of America
Publication statusPublished - 21 Jan 2020


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, c 0.75%, large-scale collective motion
emerges in the quiescent state and the flow becomes non-linear. 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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