Rapid expulsion of microswimmers by a vortical flow

Sokolov, Andrey; Aranson, Igor S.

doi:10.1038/ncomms11114

Cited by 40 publications

(72 citation statements)

References 38 publications

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“…It drags the swimmer radially outwards. Related effects are reported in recent experimental studies [104]. As a consequence, the active 2-BS is safe from getting drowned in the swirl.…”

Section: Deformable Two-bead Microswimmer In the Swirlsupporting

confidence: 62%

“…Variations of our simplified approach can serve to effectively and economically describe basic properties of microorganisms in external flows. In fact, aspects of the behavior predicted below have just been found for the motion of bacteria in imposed swirl flows [104]. Even the properties of whole colonies of connected microorganisms, such as Volvox colonies [105,106], may be characterized accordingly.…”

Section: Introductionmentioning

confidence: 81%

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Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

2016

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Deformability is a central feature of many types of microswimmers, e.g. for artificially generated self-propelled droplets. Here, we analyze deformable bead-spring microswimmers in an externally imposed solvent flow field as simple theoretical model systems. We focus on their behavior in a circular swirl flow in two spatial dimensions. Linear (straight) two-bead swimmers are found to circle around the swirl with a slight drift to the outside with increasing activity. In contrast to that, we observe for triangular three-bead or square-like four-bead swimmers a tendency of being drawn into the swirl and finally getting drowned, although a radial inward component is absent in the flow field. During one cycle around the swirl, the self-propulsion direction of an active triangular or square-like swimmer remains almost constant, while their orbits become deformed exhibiting an "egg-like" shape. Over time, the swirl flow induces slight net rotations of these swimmer types, which leads to net rotations of the egg-shaped orbits. Interestingly, in certain cases, the orbital rotation changes sense when the swimmer approaches the flow singularity. Our predictions can be verified in real-space experiments on artificial microswimmers.

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“…It drags the swimmer radially outwards. Related effects are reported in recent experimental studies [104]. As a consequence, the active 2-BS is safe from getting drowned in the swirl.…”

Section: Deformable Two-bead Microswimmer In the Swirlsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 81%

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

2016

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“…Furthermore, these defects can be guided by applied electric or magnetic fields, surface anchoring, light, or chemical and temperature gradients. These findings extend our scope of tools to control and manipulate microscopic objects in active matter [33,36,50,51]. Moreover, with the recent progress in the lithographic design of light-sensitive surface anchoring patterns, topological defects can be created on demand and guided by light [52].…”

Section: Discussionmentioning

confidence: 55%

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

et al. 2017

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Active matter exemplified by suspensions of motile bacteria or synthetic self-propelled particles exhibits a remarkable propensity to self-organization and collective motion. The local input of energy and simple particle interactions often lead to complex emergent behavior manifested by the formation of macroscopic vortices and coherent structures with long-range order. A realization of an active system has been conceived by combining swimming bacteria and a lyotropic liquid crystal. Here, by coupling the well-established and validated model of nematic liquid crystals with the bacterial dynamics, we develop a computational model describing intricate properties of such a living nematic. In faithful agreement with the experiment, the model reproduces the onset of periodic undulation of the director and consequent proliferation of topological defects with the increase in bacterial concentration. It yields a testable prediction on the accumulation of bacteria in the cores of þ1=2 topological defects and depletion of bacteria in the cores of −1=2 defects. Our dedicated experiment on motile bacteria suspended in a freestanding liquid crystalline film fully confirms this prediction. Our findings suggest novel approaches for trapping and transport of bacteria and synthetic swimmers in anisotropic liquids and extend a scope of tools to control and manipulate microscopic objects in active matter.

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“…Examples range from bird flocks [2], fish schools [3], bacteria suspensions [4,5], microtubules-molecular motors assays [6][7][8] to colloidal rollers [9] and Janus floaters [10]. Active systems often exhibit properties not present at their dynamic counterparts, such as viscosity reduction [11,12], enhanced mixing [13,14], rectification of chaotic motion [15,16], active concentration depletion [17,18] and many others.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous topological charging of tactoids in a living nematic

2018

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Living nematic is a realization of an active matter combining a nematic liquid crystal with swimming bacteria. The material exhibits a remarkable tendency towards spatio-temporal self-organization manifested in formation of dynamic textures of self-propelled half-integer topological defects (disclinations). Here we report on the study of such living nematic near normal inclusions, or tactoids, naturally realized in liquid crystals close to the isotropic-nematic (I-N) phase transition. On the basis of the computational analysis, we have established that tactoid's I-N interface spontaneously acquire negative topological charge which is proportional to the tactoid's size and depends on the concentration of bacteria. The observed negative charging is attributed to the drastic difference in the mobilities of +1/2 and −1/2 topological defects in active systems. The effect is described in the framework of a kinetic theory for point-like weakly-interacting defects with different mobilities. Our dedicated experiment fully confirmed the theoretical prediction. The results hint into new strategies for control of active matter.

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Rapid expulsion of microswimmers by a vortical flow

Cited by 40 publications

References 38 publications

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

Topological Defects in a Living Nematic Ensnare Swimming Bacteria

Spontaneous topological charging of tactoids in a living nematic

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