Surface-Directed Liquid Flow Inside Microchannels
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.
Get full access to this article
View all available purchase options and get full access to this article.
Already a Subscriber?Sign In
REFERENCES AND NOTES
1
M. Freemantle, Chem. Eng. News 77 (no. 8), 27 (1999).
2
Unger M. A., et al., Science 288, 113 (2000);
Fahrenberg J., et al., J. Micromech. Microeng. 5, 169 (1995);
Goll C., et al., J. Micromech. Microeng. 6, 77 (1996);
Yang X., Grosjean C., Tai Y. C., Ho C. M., Sens. Actuators A 64, 101 (1998).
3
Harrison D. J., et al., Science 261, 895 (1993).
4
Salimi-Moosavi H., Tang T., Harrison D. J., J. Am. Chem. Soc. 119, 8716 (1997).
5
Beni G., Tenan M. A., J. Appl. Phys. 52, 6011 (1981).
6
Gallardo B. S., et al., Science 283, 57 (1999).
7
Kataoka D. E., Troian S. M., Nature 402, 794 (1999).
8
Burns M. A., et al., Proc. Natl. Acad. Sci. U.S.A. 93, 5556 (1996).
9
A. W. Adamson, Physical Chemistry of Surfaces (Wiley, New York, ed. 5, 1990).
10
Mcdonald J. C., et al., Electrophoresis 21, 27 (2000).
11
Handique K., Gogoi B. P., Burke D. T., Mastrangleo C. H., Burns M. A., Proc. SPIE 3224, 185 (1997).
12
Delamarche E., Bernard A., Schmid H., Michel B., Biebuyck H., Science 276, 779 (1997).
13
Ichimura K., Oh S.-K., Nakagawa M., Science 288, 1624 (2000).
14
Gau H., Herminghaus S., Lenz P., Lipowsky R., Science 283, 46 (1999).
15
Darhuber A. A., Troian S. M., Miller S. M., J. Appl. Phys. 87, 7768 (2000).
16
Strook A. D., et al., Phys. Rev. Lett. 84, 3314 (2000).
17
G. T. A. Kovacs, Micromachined Transducer Sourcebook (McGraw-Hill, Boston, 1998).
18
Weigl B. H., Yager P., Science 283, 346 (1999).
19
Kenis P. J. A., Ismagilov R. F., Whiteside G. M., Science 285, 83 (1999).
20
Takayama S., et al., Proc. Natl. Acad. Sci. U.S.A. 96, 5545 (1999).
21
A. Ulman, An Introduction to Ultrathin Organic Films (Academic Press, Boston, 1991).
22
Ulman A., Chem. Rev. 96, 1533 (1996).
23
Zhao B., Mulkey D., Brittain W. J., Chen Z., Foster M. D., Langmuir 15, 6856 (1999).
24
We used hexadecane (Aldrich, 99%) as a solvent to form SAMs of trichlorosilanes on silica substrates. Contact angle measurement showed that SAMs with full coverages were formed on glass substrates in less than 2 min.
25
Beebe D. J., et al., Nature 404, 588 (2000).
26
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.
27
A pipette tip with inner diameters of 8 mm at the bottom and 6 mm at the top was fixed onto the channels. The maximum pressure that virtual walls can withstand was determined by gradually adding deionized water into the pipette and then measuring water height when a bulge developed.
28
The surface free energy of Rhodamine B dilute solution is lower than that of deionized water, resulting in a lower maximum pressure.
29
Rich D. H., Gurwara S. K., J. Am. Chem. Soc. 97, 1575 (1975);
; V. N. R. Pillai, Synthesis (Germany) (1980), p. 1.
30
Jacobson S. C., Ramsey M., Electrophoresis 16, 481 (1995).
31
Oleschuk R. D., Shultz-Lockyear L. L., Ning Y., Harrison D. J., Anal. Chem. 72, 585 (2000).
32
Beebe D. J., et al., Proc. Natl. Acad. Sci. U.S.A. 97, 13488 (2000).
33
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.
Information & Authors
Information
Published In

Science
Volume 291 | Issue 5506
9 February 2001
9 February 2001
Submission history
Received: 8 November 2000
Accepted: 4 January 2001
Published in print: 9 February 2001
Authors
Metrics & Citations
Metrics
Article Usage
Altmetrics
Citations
Export citation
Select the format you want to export the citation of this publication.
Cited by
- Microfluidic Control Using Colloidal Devices, Science, 296, 5574, (1841-1844), (2021)./doi/10.1126/science.1072133
- Under oil open-channel microfluidics empowered by exclusive liquid repellency, Science Advances, 6, 16, (2020)./doi/10.1126/sciadv.aay9919
Loading...
View Options
Get Access
Log in to view the full text
AAAS login provides access to Science for AAAS Members, and access to other journals in the Science family to users who have purchased individual subscriptions.
- Become a AAAS Member
- Activate your AAAS ID
- Purchase Access to Other Journals in the Science Family
- Account Help
Log in via OpenAthens.
Log in via Shibboleth.
More options
Purchase digital access to this article
Download and print this article for your personal scholarly, research, and educational use.
Buy a single issue of Science for just $15 USD.
View options
PDF format
Download this article as a PDF file
Download PDF





