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Electropermanent magnet-driven droplet size modulation for two-phase ferromicrofluidics

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Abstract

A new ferrofluidic droplet generator is demonstrated using an electropermanent magnet to change the viscosity of the ferrofluid oil phase in a flow-focusing junction, which enables control of the aqueous droplet size. Electropermanent magnets are capable of fast switching (< 100 \(\upmu\)s) and have magnetic field strengths comparable to those of permanent magnets. When switched on, the magnetoviscous effect increases the viscosity of the ferrofluid, thus increasing the channel’s fluidic resistance, slowing the flow rate of the oil-based phase and changing the droplet diameter. We have demonstrated on-demand droplet size modulation as large as 44% at speeds fast enough to modulate the size of a single droplet in a stream. Due to compliance in the supply tubing and Polydimethylsiloxane (PDMS) microfluidic channels, the change in droplet size relaxes with a time scale of seconds. An application of droplet size modulation was demonstrated by integrating a passive size-based magnetic droplet sorting stage.

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Acknowledgements

The authors thank Karlheinz Merkle for the wire electro-discharge machining of the EPM pole pieces. The microfabrication was performed in the Stanford Nanofabrication Facility, supported by the National Science Foundation under award ECS-1542152.

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Author notes

  1. Jose I. Padovani

    Present address: Medtronic, Sunnyvale, CA, 94085, USA

  2. Ali M. Ibrahim

    Present address: McGill University, Montreal, QC, H3A 0G4, Canada

Authors and Affiliations

  1. Department of Electrical Engineering, School of Engineering, Stanford University, Stanford, CA, 94305, USA

    Jose I. Padovani & Roger T. Howe

  2. Mechanical Design and Production Department, Faculty of Engineering, Cairo University, Giza, 12316, Egypt

    Ali M. Ibrahim & Yasser H. Anis

  3. Department of Surgery, School of Medicine, Stanford University, Stanford, CA, 94305, USA

    Stefanie S. Jeffrey

Authors
  1. Jose I. Padovani
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  2. Ali M. Ibrahim
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  3. Stefanie S. Jeffrey
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  4. Yasser H. Anis
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  5. Roger T. Howe
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Correspondence to Yasser H. Anis.

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The authors declare that they have no conflict of interest.

Funding

This work was supported in part by NIH-P01HG000205 (RTH, JIP) and NIH-R21CA177447 (SSJ).

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Padovani, J.I., Ibrahim, A.M., Jeffrey, S.S. et al. Electropermanent magnet-driven droplet size modulation for two-phase ferromicrofluidics. Microfluid Nanofluid 24, 93 (2020). https://doi.org/10.1007/s10404-020-02398-4

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