This work examines the effects of absolute pressure on fluid slip in a hydrophobic microchannel. Previous experiments with hydrophobic surfaces have indicated the presence of an apparent fluid slip. The mechanism responsible for the apparent fluid slip observed by Pit. et. al. (Phys. Rev. Lett., 85, 980–983), Zhu and Granick (Phys. Rev. Lett., 87, 096105), and Tretheway and Meinhart (Phys. of Fluids, 14, L9-L12) is unknown. Recently, Tyrell and Attard () have observed the presence of nanobubbles on a hydrophobic surface. Modeling these nanobubbles as a thin gas layer and solving for the velocity profile between two infinite parallel plates yields an apparent fluid slip consistent with the experimentally observed results. As the slip length is highly dependent on the nanobubble or gas layer thickness, increases in absolute pressure should decrease the bubble size and reduce the measured slip. This work explores the proposed mechanism by measuring velocity profiles and calculating slip lengths at varying absolute pressures.

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