Cooperative self-propulsion of active and passive rotors

Yaouen Fily, Aparna Baskaran, M. Cristina Marchetti

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


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 ∼1/r 2 to dipolar order that can yield the recently studied "cooperative self-propulsion" of a pair of rotors of opposite vorticity. It is also known, although not widely appreciated, that this interaction is identically zero for active rotors as a consequence of torque balance. In this paper we show that a ∼1/r 4 azimuthal component of the interaction arises in active systems to octupolar order. This is a new result that allows us to discuss the dynamic behavior of pairs of passive and active interacting rotors in a unified manner and to show that cooperative self-propulsion, although weaker, can also occur for pairs of active rotors.

Original languageEnglish (US)
Pages (from-to)3002-3009
Number of pages8
JournalSoft Matter
Issue number10
StatePublished - Mar 14 2012

ASJC Scopus subject areas

  • General Chemistry
  • Condensed Matter Physics


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