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Active Suspensions have Nonmonotonic Flow Curves and Multiple Mechanical Equilibria

Research output: Contribution to journalArticle

Original languageEnglish
Article number018001
Number of pages5
JournalPhysical Review Letters
Issue number1
Early online date3 Jul 2018
DateSubmitted - 1 Mar 2018
DateAccepted/In press - 4 Jun 2018
DateE-pub ahead of print - 3 Jul 2018
DatePublished (current) - 6 Jul 2018


We point out unconventional mechanical properties of confined active fluids, such as bacterial suspensions, under shear. Using a minimal model of an active liquid crystal with no free parameters, we predict the existence of a window of bacteria concentration for which a suspension of E. Coli effectively behaves, at steady-state, as a negative viscosity fluid and reach a quantitative agreement with experimental measurements. Our theoretical analysis further shows that a negative apparent viscosity is due to a nonmonotonic local velocity profile, and it is associated with a nonmonotonic stress versus strain rate flow curve. This implies that fixed stress and fixed strain rate ensembles are not equivalent for active fluids.

    Structured keywords

  • BrisSynBio
  • Bristol BioDesign Institute

    Research areas

  • Escherichia coli/chemistry, Liquid Crystals/chemistry, Models, Biological, Models, Chemical, Models, Theoretical, Suspensions, Synthetic biology

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