Superparamagnetic particle dynamics and mixing in a rotating capillary tube with a stationary magnetic field

Jun Tae Lee, Aamir Abid, Ka Ho Cheung, L. Sudheendra, Ian M. Kennedy

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


The dynamics of superparamagnetic particles subject to competing magnetic and viscous drag forces have been examined with a uniform, stationary, external magnetic field. In this approach, competing drag and magnetic forces were created in a fluid suspension of superparamagnetic particles that was confined in a capillary tube; competing viscous drag and magnetic forces were established by rotating the tube. A critical Mason number was determined for conditions under which the rotation of the capillary prevents the formation of chains from individual particles. The statistics of chain length was investigated by image analysis while varying parameters such as the rotation speed and the viscosity of the liquid. The measurements showed that the rate of particle chain formation was decreased with increased viscosity and rotation speed; the particle dynamics could be quantified by the same dimensionless Mason number that has been demonstrated for rotating magnetic fields. The potential for enhancement of mixing in a bioassay was assessed using a fast chemical reaction that was diffusion-limited. Reducing the Mason number below the critical value, so that chains were formed in the fluid, gave rise to a modest improvement in the time to completion of the reaction.

Original languageEnglish (US)
Pages (from-to)461-468
Number of pages8
JournalMicrofluidics and Nanofluidics
Issue number3
StatePublished - Sep 2012


  • Magnetic particles
  • Mason number
  • Particle chains
  • Rotating capillary

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials
  • Materials Chemistry


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