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Microdroplet formation in rounded flow-focusing junctions

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Abstract

Herein we report microfluidic droplet formation in flow-focusing geometries possessing varying degrees of rounding. Rounding is incorporated in all four corners (symmetric) or only in the two exit corners (asymmetric). The ratios of the radius of curvature, R, to channel width, w, are varied where R/w = 0, 0.5 and 1. In all cases, monodisperse droplets are produced, with the largest droplets being produced at the junctions with the largest rounding. Junctions without rounding are shown to produce droplets at higher frequencies than those with rounding. Droplet pinch-off position is found to be dependent on both geometry and volumetric flow rates; the location shifts toward the interior of the rounded junctions with increasing oil-to-water flow rate ratios. Accordingly, we find that rounding within microfluidic flow-focusing junctions strongly influences droplet formation. Junction rounding may be deliberate due to the selected fabrication method or occur as an unintended result of microfabrication processes not held to strict tolerances. Indeed, understanding droplet characteristics for those formed in such structures is critical for microfluidic applications where droplet volume or reagent mass must be well controlled. Thus, rounding can be a valuable design parameter when tuning the size and production frequency for emulsion collection or ensuing downstream operations such as chemical reactions.

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Acknowledgments

This work was supported in part by the RCUK Microdroplets Basic Technology Project (EP/D048664/1). The authors would like to thank Joshua B. Edel and Andrew J. deMello for useful discussions and the use of their cleanroom facilities to fabricate devices. SG and WG would like to acknowledge support from the School of Engineering and Computer Science at University of the Pacific.

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Authors and Affiliations

  1. School of Engineering and Computer Science, Bioengineering Program, University of the Pacific, Stockton, CA, USA

    Shelly Gulati, Wilson W. Good, Warren L. Tamayo & Akhil R. Patel

  2. Department of Chemistry, Imperial College London, London, UK

    Kalpana Vijayakumar

  3. Faculty of Engineering and the Environment, University of Southampton, Southampton, UK

    Xize Niu

Authors
  1. Shelly Gulati
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  2. Kalpana Vijayakumar
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  3. Wilson W. Good
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  4. Warren L. Tamayo
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  5. Akhil R. Patel
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  6. Xize Niu
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Correspondence to Shelly Gulati.

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Gulati, S., Vijayakumar, K., Good, W.W. et al. Microdroplet formation in rounded flow-focusing junctions. Microfluid Nanofluid 20, 2 (2016). https://doi.org/10.1007/s10404-015-1680-3

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  • DOI: https://doi.org/10.1007/s10404-015-1680-3

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