We report our study of an interfacial gas phase formed between a smooth hydrophobic surface and water using pool boiling experiments. Nanoscopically smooth hydrophobic islands of 10 ∼ 100 μm in width are fabricated on a hydrophilic silicon substrate using photolithography. We observe sustained bubble nucleation at superheat as low as 9 °C. The amount of dissolved gas in water does not have a significant effect on bubble nucleation. By comparing the measured minimum superheat for the onset of bubble nucleation with theoretical prediction, we provide indirect evidence for the presence of an interfacial gas phase with widths on the order of 1 μm and contact angle >160°. This high contact angle, which has been postulated to be the reason for the long lifetime of nanobubbles, drastically decreases the nucleation barrier, even on nanoscopically smooth hydrophobic surfaces.

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