Rotating colloids in rotating magnetic fields: Dipolar relaxation and hydrodynamic coupling

Anna C. H. Coughlan and Michael A. Bevan
Phys. Rev. E 94, 042613 – Published 26 October 2016
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Abstract

Video microscopy (VM) experiments and Brownian dynamics (BD) simulations were used to measure and model superparamagnetic colloidal particles in rotating magnetic fields for interaction energies on the order of the thermal energy, kT. Results from experiments and simulations were compared for isolated particle rotation, particle rotation within doublets, doublet rotation, and separation within doublets vs field rotation frequency. Agreement between VM and BD results was obtained at all frequencies and amplitudes only by including exact two-body hydrodynamic interactions and relevant relaxation times of magnetic dipoles. Frequency-dependent particle forces and torques cause doublets to rotate at low frequencies via dipolar interactions and at high frequencies via hydrodynamic translation-rotation coupling. By matching measurements and simulations for a range of conditions, our findings unambiguously demonstrate the quantitative forms of dipolar and hydrodynamic interactions necessary to capture nonequilibrium, steady-state dynamics of Brownian colloids in magnetic fields.

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  • Received 5 July 2016
  • Revised 16 August 2016

DOI:https://doi.org/10.1103/PhysRevE.94.042613

©2016 American Physical Society

Physics Subject Headings (PhySH)

Fluid DynamicsStatistical Physics & ThermodynamicsPolymers & Soft Matter

Authors & Affiliations

Anna C. H. Coughlan and Michael A. Bevan*

  • Chemical & Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA

  • *mabevan@jhu.edu

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Issue

Vol. 94, Iss. 4 — October 2016

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