Active suspensions have non-monotonic flow curves and multiple mechanical equilibria

Abstract

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 \textit{E.~Coli} effectively behaves, at steady-state, as a negative viscosity fluid and reach quantitative agreement with experimental measurements. Our theoretical analysis further shows that a negative apparent viscosity is due to a non-monotonic local velocity profile, and is associated with a non-monotonic stress vs. strain rate flow curve. This implies that fixed stress and fixed strain rate ensembles are not equivalent for active fluids.

arXiv comment5 pages, 4 figures

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Cited by in corpus (13)

• Lattice Boltzmann Methods and Active Fluids
• Cascade or not cascade? Energy transfer and elastic effects in active nematics
• Shear-induced first-order transition in polar liquid crystals
• Thin-Film Modelling of Resting and Moving Active Droplets
• Multi-scale control of active emulsion dynamics
• Tractionless Self-Propulsion of Active Drops
• Rheology of active polar emulsions: from linear to unidirectional and unviscid flow, and intermittent viscosity
• Stress relaxation in a dilute bacterial suspension: The active-passive transition
• Rheology of active emulsions with negative effective viscosity
• Stokes' second problem and reduction of inertia in active fluids
• Forced microrheology of active colloids
• Exact results for sheared polar active suspensions with variable liquid crystalline order
• Lattice Boltzmann simulations of self-propelling chiral active droplets