In this paper the interfacial characteristics of a liquid flowing over a 1cm2 array of hydrophobic cylindrical micropillars located within a microchannel are investigated. The microchannel was 12mm wide and 32mm long with an average channel height of approximately 83μm. Hydrophobic coating of the channel was achieved via a controlled flow of a trichlorosilane and ethanol solution. A method to remove lodged gas bubbles from a microchannel was successfully demonstrated, while maintaining the favorable Cassie-Baxter wetting state (gas/vapor layer present) of the micropillar structures. This was achieved using degassed water to dissolve low-curvature gas bubbles, while ohmically heating the silicon substrate to reassert and maintain the Cassie-Baxter wetting state of the hydrophobic micropillars. During this experimentation it was discovered that the part wetting and dewetting of a superhydrophobic (SH) surface within a microchannel could be achieved using similar methods. The onset of surface wetting (Wenzel wetting state) was achieved by pumping degassed water through the microchannel. Surface dewetting was then accomplished through substrate heating by the increase in the trapped gas layer pressure, the water vapor pressure and outgassing from the lightly degassed fluid. These reactions force the gas/vapor layer to expand laterally throughout the micropillar array, thus restoring the Cassie-Baxter wetting state. The reported results demonstrate a low-power method for effectively reversing the Wenzel wetting state of a SH surface under microchannel flow conditions and may prove to be a useful technique for manipulating fluid flow within microfluidic devices.

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