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Control of Initiation, Rate, and Routing of Spontaneous Capillary-Driven Flow of Liquid Droplets through Microfluidic Channels on SlipChip

Pompano, Rebecca R. and Platt, Carol E. and Karymov, Mikhail A. and Ismagilov, Rustem F. (2012) Control of Initiation, Rate, and Routing of Spontaneous Capillary-Driven Flow of Liquid Droplets through Microfluidic Channels on SlipChip. Langmuir, 28 (3). pp. 1931-1941. ISSN 0743-7463. PMCID PMC3271727. doi:10.1021/la204399m.

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This Article describes the use of capillary pressure to initiate and control the rate of spontaneous liquid–liquid flow through microfluidic channels. In contrast to flow driven by external pressure, flow driven by capillary pressure is dominated by interfacial phenomena and is exquisitely sensitive to the chemical composition and geometry of the fluids and channels. A stepwise change in capillary force was initiated on a hydrophobic SlipChip by slipping a shallow channel containing an aqueous droplet into contact with a slightly deeper channel filled with immiscible oil. This action induced spontaneous flow of the droplet into the deeper channel. A model predicting the rate of spontaneous flow was developed on the basis of the balance of net capillary force with viscous flow resistance, using as inputs the liquid–liquid surface tension, the advancing and receding contact angles at the three-phase aqueous–oil–surface contact line, and the geometry of the devices. The impact of contact angle hysteresis, the presence or absence of a lubricating oil layer, and adsorption of surface-active compounds at liquid–liquid or liquid–solid interfaces were quantified. Two regimes of flow spanning a 104-fold range of flow rates were obtained and modeled quantitatively, with faster (mm/s) flow obtained when oil could escape through connected channels as it was displaced by flowing aqueous solution, and slower (micrometer/s) flow obtained when oil escape was mostly restricted to a micrometer-scale gap between the plates of the SlipChip (“dead-end flow”). Rupture of the lubricating oil layer (reminiscent of a Cassie–Wenzel transition) was proposed as a cause of discrepancy between the model and the experiment. Both dilute salt solutions and complex biological solutions such as human blood plasma could be flowed using this approach. We anticipate that flow driven by capillary pressure will be useful for the design and operation of flow in microfluidic applications that do not require external power, valves, or pumps, including on SlipChip and other droplet- or plug-based microfluidic devices. In addition, this approach may be used as a sensitive method of evaluating interfacial tension, contact angles, and wetting phenomena on chip.

Item Type:Article
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URLURL TypeDescription CentralArticle
Ismagilov, Rustem F.0000-0002-3680-4399
Additional Information:© 2012 American Chemical Society. Received: November 8, 2011. Revised: December 19, 2011. Publication Date (Web): January 10, 2012. T his work was supported by DARPA Grant No. 11-39-DxODLRS-FP-016 and NIH Grant No. 1R01 EB012946 administered by the National Institute of Biomedical Imaging and Bioengineering. We thank Liang Li for discussions of chip design and oil rupture, Tom Witten for discussions of fluid instabilities, Stefano Begolo for discussions of pressures vs forces, and for considering the Cassie−Wenzel transition and means to test it, and Toan Huynh for developing the FEP dipping protocol. We thank Heidi Park for contributions to writing and editing this manuscript. R.F.I. has a financial interest in SlipChip LLC.
Funding AgencyGrant Number
Defense Advanced Research Projects Agency (DARPA)11-39-DxOD-LRS-FP-016
NIH1R01 EB012946
Issue or Number:3
PubMed Central ID:PMC3271727
Record Number:CaltechAUTHORS:20120222-071637506
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Official Citation:Control of Initiation, Rate, and Routing of Spontaneous Capillary-Driven Flow of Liquid Droplets through Microfluidic Channels on SlipChip Rebecca R. Pompano, Carol E. Platt, Mikhail A. Karymov, and Rustem F. Ismagilov Langmuir 2012 28 (3), 1931-1941
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29400
Deposited By: Ruth Sustaita
Deposited On:22 Feb 2012 15:43
Last Modified:09 Nov 2021 17:06

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