Patterning liquid flow on the microscopic scale

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Abstract

Microscopic fluidic devices, ranging from surgical endoscopes1 and microelectromechanical systems2 to the commercial ‘lab-on-a-chip’ (ref. 29), allow chemical analysis and synthesis on scales unimaginable a decade ago. These devices transport miniscule quantities of liquid along networked channels. Several techniques have been developed to control small-scale flow, including micromechanical3 and electrohydrodynamic4 pumping, electro-osmotic flow5, electrowetting6,7 and thermocapillary pumping8,9,10. Most of these schemes require micro-machining of interior channels and kilovolt sources to drive electrokinetic flow. Recent work8,9,10 has suggested the use of temperature instead of electric fields to derive droplet movement. Here we demonstrate a simple, alternative technique utilizing temperature gradients to direct microscopic flow on a selectively patterned surface (consisting of alternating stripes of bare and coated SiO2). The liquid is manipulated by simultaneously applying a shear stress at the air–liquid interface and a variable surface energy pattern at the liquid–solid interface. To further this technology, we provide a theoretical estimate of the smallest feature size attainable with this technique.

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Figure 1: Schematic diagrams of the experimental apparatus (a) and the orientation of the patterned Si wafer (b).
Figure 2: Time series of a silicone-oil film spreading on a patterned silicon wafer.
Figure 3: Comparison between the location of the liquid front for spreading on a patterned and an homogeneous surface.

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Acknowledgements

We thank G. D. Barriac for assisting with the photolithographic patterning of the silicon wafers. This work was supported by the National Science Foundation through a graduate fellowship (D.E.K.) and a CAREER award (S.M.T.).

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Correspondence to Sandra M. Troian.

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Kataoka, D., Troian, S. Patterning liquid flow on the microscopic scale. Nature 402, 794–797 (1999) doi:10.1038/45521

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