Control of microswimmers by spiral nematic vortices: Transition from individual to collective motion and contraction, expansion, and stable circulation of bacterial swirls

Runa Koizumi, Taras Turiv, Mikhail M. Genkin, Robert J. Lastowski, Hao Yu, Irakli Chaganava, Qi Huo Wei, Igor S. Aranson, Oleg D. Lavrentovich

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Active systems composed of self-propelled units show fascinating transitions from Brownian-like dynamics to collective coherent motion. Swirling of swimming bacteria is a spectacular example. This study demonstrates that a nematic liquid crystal environment patterned as a spiral vortex controls individual-to-collective transition in bacterial swirls and defines whether they expand or shrink. In dilute dispersions, the bacteria swim along open spiral trajectories, following the preimposed molecular orientation. The trajectories are nonpolar. As their concentration exceeds some threshold, the bacteria condense into unipolar circular swirls resembling stable limit cycles. This collective circular motion is controlled by the spiral angle that defines the splay-to-bend ratio of the background director. Vortices with dominating splay shrink the swirls toward the center, while vortices with dominating bend expand them to the periphery. Spiraling vortices of 45ã with splay-bend parity produce the most stable swirls. All the dynamic scenarios are explained by hydrodynamic interactions of bacteria mediated by the patterned passive nematic environment and by the coupling between the concentration and orientation. The acquired knowledge of how to control individual and collective motion of microswimmers by a nematic environment can help in the development of microscopic mechanical systems.

Original languageEnglish (US)
Article number033060
JournalPhysical Review Research
Volume2
Issue number3
DOIs
StatePublished - Jul 2020

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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