This work examines the effects of soluble gasses and absolute pressure on fluid slip in a hydrophobic microchannel. Previous experiments with hydrophobic surfaces have indicated the presence of an apparent fluid slip. Tretheway and Meinhart (Phys. of Fluids 16, 1509) proposed a 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). Tyrell and Attard (Phys. Rev. Lett. 87, 176104) observed the presence of nanobubbles on a hydrophobic surface. Tretheway and Meinhart (Phys. of Fluids 16, 1509) modeled these nanobubbles as a thin gas layer and solved for the velocity profile between two infinite parallel plates, which 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, varying the soluble gas concentration or absolute pressure should increase and decrease the apparent fluid slip. This work explores the proposed mechanism by measuring velocity profiles and calculating slip lengths for various saturated and degassed solutions and a range of absolute pressures.

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