title: Rapid expulsion of microswimmers by a vortical flow.
abstract: Interactions of microswimmers with their fluid environment are exceptionally complex. Macroscopic shear flow alters swimming trajectories in a highly nontrivial way and results in dramatic reduction of viscosity and heterogeneous bacterial distributions. Here we report on experimental and theoretical studies of rapid expulsion of microswimmers, such as motile bacteria, by a vortical flow created by a rotating microparticle. We observe a formation of a macroscopic depletion area in a high-shear region, in the vicinity of a microparticle. The rapid migration of bacteria from the shear-rich area is caused by a vortical structure of the flow rather than intrinsic random fluctuations of bacteria orientations, in stark contrast to planar shear flow. Our mathematical model reveals that expulsion is a combined effect of motility and alignment by a vortical flow. Our findings offer a novel approach for manipulation of motile microorganisms and shed light on bacteria-flow interactions.
authors.affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Andrey
authors.initials: A
authors.lastname: Sokolov
authors.affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.|Department of Engineering Sciences and Applied Mathematics, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60202, USA.
authors.forename: Igor S
authors.initials: IS
authors.lastname: Aranson
mesh_terms: D000465:Algorithms; D001412:Bacillus subtilis; D001419:Bacteria; D057446:Hydrodynamics; D008124:Locomotion; D008962:Models, Theoretical; D013314:Stress, Mechanical; D014783:Viscosity