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Mechanisms of rectangular groove-induced multiple-microdroplet coalescences

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Abstract

The mechanism of microdroplet coalescence is a fundamental issue for droplet-based microfluidics. We developed an asymmetric expansion (a rectangular groove) along one side of a microchannel to achieve multiple-microdroplet trapping, collision, and coalescence. Compared with reported symmetric expansions, this asymmetric groove could easily trap microdroplets and control two or three microdroplet coalescences precisely without a requirement for temporal and spatial synchronization. To reveal the mechanisms of multiple-droplet coalescences in a groove, we observed five different coalescence patterns under different flow conditions. Moreover, we characterized the flow behavior quantitatively by simulating the velocity vector fields in both the microdroplets and continuous phase, finding good agreement with experiments. Finally, a map of coalescence forms with different capillary numbers (\(0.001< {Ca} <0.016\)) and flow ratios (\(0.1<e<0.9\)) was obtained. The results could provide a useful guidance for the design and application of droplet-based microfluidic devices.

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Acknowledgements

This work was supported by the Beijing Municipal Natural Science Foundation (Grant 7152012), the General Program of Science and Technology Development Project of the Beijing Municipal Education Commission (Grant KM201610005002), the National Natural Science Foundation of China (Grant 11572013), the China Scholarship Council (Grant 201406545031), and the Training Plan of New Talent of Beijing University of Technology (Grant 2015-RX-L02).

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Authors and Affiliations

  1. College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing, 100124, China

    Feng Shen, Yi Li & Zhaomiao Liu

  2. Department of Mechanical Engineering and Biomedical Engineering Program, University of South Carolina, Columbia, SC, 29208, USA

    Feng Shen & Guiren Wang

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  1. Feng Shen
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  2. Yi Li
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  3. Guiren Wang
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  4. Zhaomiao Liu
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Correspondence to Feng Shen or Zhaomiao Liu.

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Shen, F., Li, Y., Wang, G. et al. Mechanisms of rectangular groove-induced multiple-microdroplet coalescences. Acta Mech. Sin. 33, 585–594 (2017). https://doi.org/10.1007/s10409-016-0623-x

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