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Abstract

Self-assembled monolayer chemistry was used in combination with either multistream laminar flow or photolithography to pattern surface free energies inside microchannel networks. Aqueous liquids introduced into these patterned channels are confined to the hydrophilic pathways, provided the pressure is maintained below a critical value. The maximum pressure is determined by the surface free energy of the liquid, the advancing contact angle of the liquid on the hydrophobic regions, and the channel depth. Surface-directed liquid flow was used to create pressure-sensitive switches inside channel networks. The ability to confine liquid flow inside microchannels with only two physical walls is expected to be useful in applications where a large gas-liquid interface is critical, as demonstrated here by a gas-liquid reaction.
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Hexadecane and the solution of trichlorosilane in hexadecane [0.5 weight-to-volume percent (w/v %)] were pumped into channels by two syringe pumps (Harvard Apparatus PHD 2000 Programmable). Syringes were connected to pipette tips fixed to channels by silicone tubing (Helix Medical, 0.040" ID/0.085" OD). Because the reactivity of trichlorosilanes is high, solvent was always introduced into the channel before the silane solution to eliminate the formation of SAMs in unwanted areas. At the end of the process, flow of the silane solution was always halted before stopping the flow of pure solvent. The flow rates of solvent and solution were usually the same, either 1 or 2 ml/min; the flow time was 2 to 3 min. The channels were cleaned by sequentially flushing with 10 ml of hexane and 10 ml of methanol followed by drying with a stream of clean air or nitrogen.
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Supported by a grant from the Defense Advanced Research Projects Agency (MTO F30602-00-1-0570) (A. Lee, Program Manager). We acknowledge J. Orlicki for assisting with the images and Q. Yu for help in generating the photomasks.

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Published In

Science
Volume 291 | Issue 5506
9 February 2001

Submission history

Received: 8 November 2000
Accepted: 4 January 2001
Published in print: 9 February 2001

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Authors

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Bin Zhao
The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Jeffrey S. Moore*
The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
David J. Beebe
Department of Biomedical Engineering, University of Wisconsin–Madison, Madison, WI 53706, USA.

Notes

*
To whom correspondence should be addressed. E-mail: [email protected]

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