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Issue 11, 2014
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Hydrodynamic capture of microswimmers into sphere-bound orbits

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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.

Graphical abstract: Hydrodynamic capture of microswimmers into sphere-bound orbits

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Article information

07 Nov 2013
20 Jan 2014
First published
22 Jan 2014

Soft Matter, 2014,10, 1784-1789
Article type

Hydrodynamic capture of microswimmers into sphere-bound orbits

D. Takagi, J. Palacci, A. B. Braunschweig, M. J. Shelley and J. Zhang, Soft Matter, 2014, 10, 1784
DOI: 10.1039/C3SM52815D

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