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arXiv · 1107.0347

Cooperative Self-Propulsion of Active and Passive Rotors

Yaouen Fily·Aparna Baskaran·M. Cristina Marchetti
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Abstract

Using minimal models for low Reynolds number passive and active rotors in a fluid, we characterize the hydrodynamic interactions among rotors and the resulting dynamics of a pair of interacting rotors. This allows us to treat in a common framework passive or externally driven rotors, such as magnetic colloids driven by a rotating magnetic field, and active or internally driven rotors, such as sperm cells confined at boundaries. The hydrodynamic interaction of passive rotors is known to contain an azimuthal component \sim 1/r^2 to dipolar order that can yield the recently discovered "cooperative self-propulsion" of a pair of rotors of opposite vorticity. While this interaction is identically zero for active rotors as a consequence of torque balance, we show that a \sim 1/r^4 azimuthal component of the interaction arises in active systems to octupolar order. Cooperative self-propulsion, although weaker, can therefore also occur for pairs of active rotors.

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Yaouen Fily, Aparna Baskaran, M. Cristina Marchetti. 2011-07-02. Cooperative Self-Propulsion of Active and Passive Rotors. https://doi.org/10.1039/c2sm06952k

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