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Published September 1, 2001 | public
Journal Article Open

Dynamics of capillary spreading along hydrophilic microstripes


We have studied the capillary spreading of a Newtonian liquid along hydrophilic microstripes that are chemically defined on a hydrophobic substrate. The front of the spreading film advances in time according to a power law x=Bt1/2. This exponent of 1/2 is much larger than the value 1/10 observed in the axisymmetric spreading of a wetting droplet. It is identical to the exponent found for wicking in open or closed microchannels. Even though no wicking occurs in our system, the influence of surface curvature induced by the lateral confinement of the liquid stripe also leads to an exponent of 1/2 but with a strongly modified prefactor B. We obtain excellent experimental agreement with the predicted time dependence of the front location and the dependence of the front speed on the stripe width. Additional experiments and simulations reveal the influence of the reservoir volume, liquid material parameters, edge roughness, and nonwetting defects. These results are relevant to liquid dosing applications or microfluidic delivery systems based on free-surface flow.

Additional Information

©2001 The American Physical Society Received 16 January 2001; published 13 August 2001 Financial sponsors of this work include the Princeton Center for Complex Materials (DMR-9809483), the NSF XYZ on a Chip program (CTS-0088774), the NSF POWRE Program (CTS-997353), and the DARPA-MTO Program on Molecular Level Printing. Discussions with Sigurd Wagner, Scott M. Miller, and Jeffrey M. Davis are gratefully acknowledged.


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