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Issue 7, 2008
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Interfacial instabilities in a microfluidic Hele-Shaw cell

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This paper describes surfactant-sensitive, dynamic instabilities that occur to aqueous droplets translating in a continuous flow of hexadecane in a microfluidic Hele-Shaw cell (HSC). A very low interfacial tension (on the order of 0.01 mN m−1) between water and hexadecane allowed for deformation of the droplets along the fields of flow and tip-streaming from moving droplets. In the system of water and hexadecane that we investigated, the use of surfactants in both fluids was necessary to achieve interfacial tension sufficiently low for the instabilities to occur. The droplets entering the HSC stretched orthogonally to the main direction of flow into elongated shapes, with aspect ratios greater than ten to one (width to length). These droplets exhibited two types of instabilities. The first included elongation of droplets, and Rayleigh–Plateau instabilities in the stretched droplets. Arrays of these stretched droplets formed three characteristic patterns that depended on the rates of flow of water and hexadecane. The second was driven by the shear stress exerted on the interface between the two fluids by the top and bottom boundaries of the HSC; this instability is named a “shear-driven instability” (SDI). Our observations supported that the SDI—an effect similar to tip-streaming—resulted from a redistribution of surfactants at the interface between the two fluids.

Graphical abstract: Interfacial instabilities in a microfluidic Hele-Shaw cell

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The article was received on 15 Oct 2007, accepted on 14 Apr 2008 and first published on 08 May 2008

Article type: Paper
DOI: 10.1039/B715867J
Citation: Soft Matter, 2008,4, 1403-1413
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    Interfacial instabilities in a microfluidic Hele-Shaw cell

    M. Hashimoto, P. Garstecki, H. A. Stone and G. M. Whitesides, Soft Matter, 2008, 4, 1403
    DOI: 10.1039/B715867J

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