Linear viscoelasticity of a dilute active suspension

Bechtel, Toni M.; Khair, Aditya S.

doi:10.1007/s00397-016-0991-y

Cited by 16 publications

(18 citation statements)

References 38 publications

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“…The authors verified the absence of collective motion at these volume fractions based on the velocity profile in the cone-plate rheometer being a simple shear. This decrease in the viscosity, in the absence of collective motion, has been explained based on both the Stokes–Smoluchowski (Bechtel & Khair 2017; Nambiar et al. 2017) and Landau–deGennes (Hatwalne et al.…”

Section: Resultsmentioning

confidence: 92%

“…The flow perturbation created by the tail-actuated swimming mechanism of the oriented bacteria (termed 'pushers') reinforces the fluid flow along the extensional axis of the imposed shear. Hence, the suspension viscosity is reduced below that of the solvent (Hatwalne et al 2004;Sokolov & Aranson 2009;Saintillan 2010;Gachelin et al 2013;López et al 2015;Bechtel & Khair 2017;Nambiar, Nott & Subramanian 2017;Saintillan 2018;Nambiar et al 2019b). This is in sharp contrast to suspensions with passive microstructural elements which always resist the imposed shear, leading to an enhanced viscosity (Batchelor 1970).…”

Section: Introductionmentioning

confidence: 96%

“…2013; López et al. 2015; Bechtel & Khair 2017; Nambiar, Nott & Subramanian 2017; Saintillan 2018; Nambiar et al. 2019 b ).…”

Section: Introductionmentioning

confidence: 99%

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Concentration banding instability of a sheared bacterial suspension

2020

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Section: Resultsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 96%

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Concentration banding instability of a sheared bacterial suspension

2020

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“…Later theory by Giomi et al revealed even richer dynamics and predicted the existence of shear banding, yield stress, and "superfluidity" of active fluids (22). Unusual rheology of active fluids has also been studied based on the microhydrodynamics of microswimmers at low concentrations (23)(24)(25)(26)(27), swimming pressures (28) and gener-alized Navier-Stokes equations (29). Experimentally, Sokolov et al and Gachelin et al showed the low viscosity of bacterial suspensions in thin films (30,31).…”

mentioning

confidence: 99%

Symmetric shear banding and swarming vortices in bacterial superfluids

Guo

Samanta

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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Bacterial suspensions-a premier example of active fluids-show an unusual response to shear stresses. Instead of increasing the viscosity of the suspending fluid, the emergent collective motions of swimming bacteria can turn a suspension into a superfluid with zero apparent viscosity. Although the existence of active superfluids has been demonstrated in bulk rheological measurements, the microscopic origin and dynamics of such an exotic phase have not been experimentally probed. Here, using high-speed confocal rheometry, we study the dynamics of concentrated bacterial suspensions under simple planar shear. We find that bacterial superfluids under shear exhibit unusual symmetric shear bands, defying the conventional wisdom on shear banding of complex fluids, where the formation of steady shear bands necessarily breaks the symmetry of unsheared samples. We propose a simple hydrodynamic model based on the local stress balance and the ergodic sampling of nonequilibrium shear configurations, which quantitatively describes the observed symmetric shear-banding structure. The model also successfully predicts various interesting features of swarming vortices in stationary bacterial suspensions. Our study provides insights into the physical properties of collective swarming in active fluids and illustrates their profound influences on transport processes.

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“…Such an effect, first explained by Hatwalne et al (Hatwalne et al 2004), leads to a reduction of the resistance of pusher suspensions to shear and the decrease of suspension viscosity. Incorporating further orientational dynamics of bacteria, continuum kinetic theories have been constructed based on the above picture, which quantitatively explained the rheology of dilute bacterial suspensions (Haines et al 2009;Saintillan 2010;Ryan et al 2011;Moradi and Najafi 2015;Alonso-Matilla, Ezhilan, and Saintillan 2016;Bechtel and Khair 2017). Hydrodynamic models have also been developed along a similar line (Cates et al 2008;Giomi, Liverpool, and Marchetti 2010;Slomka and Dunkel 2017), which successfully predicted the existence of bacterial superfluids with zero apparent viscosity (Marchetti 2015).…”

Section: Introductionmentioning

confidence: 99%

Rheology of bacterial suspensions under confinement

2019

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As a paradigmatic model of active fluids, bacterial suspensions show intriguing rheological responses drastically different from their counterpart colloidal suspensions. Although the flow of bulk bacterial suspensions has been extensively studied, the rheology of bacterial suspensions under confinement has not been experimentally explored. Here, using a microfluidic viscometer, we systematically measure the rheology of dilute E. coli suspensions under different degrees of confinement. Our study reveals a strong confinement effect: the viscosity of bacterial suspensions decreases substantially when the confinement scale is comparable or smaller than the run length of bacteria. Moreover, we also investigate the microscopic dynamics of bacterial suspensions including velocity profiles, bacterial density distributions and single bacterial dynamics in shear flows. These measurements allow us to construct a simple heuristic model based on the boundary layer of upstream swimming bacteria near confining walls, which qualitatively explains our experimental observations. Our study sheds light on the influence of the boundary layer of collective bacterial motions on the flow of confined bacterial suspensions. Our results provide a benchmark for testing different rheological models of active fluids and are useful for understanding the transport of microorganisms in confined geometries.

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Linear viscoelasticity of a dilute active suspension

Cited by 16 publications

References 38 publications

Concentration banding instability of a sheared bacterial suspension

Concentration banding instability of a sheared bacterial suspension

Symmetric shear banding and swarming vortices in bacterial superfluids

Rheology of bacterial suspensions under confinement

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