Surface-directed boundary flow in microfluidic channels

Tom T. Huang, David G. Taylor, Kwan Seop Lim, Miroslav Sedlak, Rashid Bashir, Nathan S. Mosier, Michael R. Ladisch

Research output: Contribution to journalArticlepeer-review


Channel geometry combined with surface chemistry enables a stable liquid boundary flow to be attained along the surfaces of a 12 μm diameter hydrophilic glass fiber in a closed semi-elliptical channel. Surface free energies and triangular corners formed by PDMS/glass fiber or OTS/glass fiber surfaces are shown to be responsible for the experimentally observed wetting phenomena and formation of liquid boundary layers that are 20-50 μm wide and 12 μm high. Viewing this stream through a 20 μm slit results in a virtual optical window with a 5 pL liquid volume suitable for cell counting and pathogen detection. The geometry that leads to the boundary layer is a closed channel that forms triangular corners where glass fiber and the OTS coated glass slide or PDMS touch. The contact angles and surfaces direct positioning of the fluid next to the fiber. Preferential wetting of corner regions initiates the boundary flow, while the elliptical cross-section of the channel stabilizes the microfluidic flow. The Young-Laplace equation, solved using fluid dynamic simulation software, shows contact angles that exceed 105° will direct the aqueous fluid to a boundary layer next to a hydrophilic fiber with a contact angle of 5°. We believe this is the first time that an explanation has been offered for the case of a boundary layer formation in a closed channel directed by a triangular geometry with two hydrophobic wetting edges adjacent to a hydrophilic surface.

Original languageEnglish (US)
Pages (from-to)6429-6437
Number of pages9
Issue number14
StatePublished - Jul 4 2006
Externally publishedYes

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry


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