Role of geometry and fluid properties in droplet and thread formation processes in planar flow focusing

Wingki Lee, Lynn M. Walker, Shelley L. Anna

Research output: Contribution to journalArticlepeer-review

191 Scopus citations


Droplet formation processes in microfluidic flow focusing devices have been examined previously and some of the key physical mechanisms for droplet formation revealed. However, the underlying physical behavior is still too poorly understood to utilize it for generating droplets of precise size. In this work, we formulate scaling arguments to define dimensionless variables which capture all the parameters that control the droplet breakup process, including the flow rates and the viscosities of the two immiscible fluids, the interfacial tension between the fluids and the numerous dimensions in the flow focusing device. To test these arguments, we perform flow focusing experiments and systematically vary the dimensional parameters. Through these experiments, we confirm the validity of the scaling arguments and find a power law relationship between the normalized droplet size and the capillary number. We demonstrate that droplet formation can be separated into an upstream process for primary droplet formation and a downstream process for thread formation. These results are key to the ability to tune the flow focusing process for specific applications that require monodisperse micron and submicron droplets and particles.

Original languageEnglish (US)
Article number032103
JournalPhysics of Fluids
Issue number3
StatePublished - 2009
Externally publishedYes

Bibliographical note

Funding Information:
This research was supported by the National Science Foundation under Grant Nos. CBET-0608864 and CBET-0730727. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research.


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