Hydrodynamic capture of microswimmers into sphere-bound orbits

Daisuke Takagi; Jeremie Palacci; Adam B. Braunschweig; Michael J. Shelley; Jun Zhang

doi:10.1039/c3sm52815d

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arXiv · 1309.5662

Hydrodynamic capture of microswimmers into sphere-bound orbits

Daisuke Takagi·Jeremie Palacci·Adam B. Braunschweig·Michael J. Shelley·Jun Zhang

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Abstract

Self-propelled particles can exhibit surprising non-equilibrium behaviors, and how they interact with obstacles or boundaries remains an important open problem. Here we show that chemically propelled micro-rods can be captured, with little change in their speed, into close orbits around solid spheres resting on or near a horizontal plane. We show that this interaction between sphere and particle is short-range, occurring even for spheres smaller than the particle length, and for a variety of sphere materials. We consider a simple model, based on lubrication theory, of a force- and torque-free swimmer driven by a surface slip (the phoretic propulsion mechanism) and moving near a solid surface. The model demonstrates capture, or movement towards the surface, and yields speeds independent of distance. This study reveals the crucial aspects of activity-driven interactions of self-propelled particles with passive objects, and brings into question the use of colloidal tracers as probes of active matter.

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Daisuke Takagi, Jeremie Palacci, Adam B. Braunschweig, Michael J. Shelley, Jun Zhang. 2013-09-22. Hydrodynamic capture of microswimmers into sphere-bound orbits. https://doi.org/10.1039/c3sm52815d

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