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

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 t...

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Bibliographic Details
Published in:Physics of fluids (1994) 2009-03, Vol.21 (3), p.032103-032103-14
Main Authors: Lee, Wingki, Walker, Lynn M., Anna, Shelley L.
Format: Article
Language:English
Subjects:
Applied fluid mechanics
Drops and bubbles
Exact sciences and technology
Fluid dynamics
Fluidics
Fundamental areas of phenomenology (including applications)
Nonhomogeneous flows
Physics
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Summary: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.
ISSN:1070-6631
1089-7666
DOI:10.1063/1.3081407