Condensation of Dissolved Gas Molecules at a Hydrophobic/Water Interface

Abstract

The non-wetting phenomenon of water on certain solid surfaces has been under intensive study for decades, but the nature of the hydrophobic/water interfaces remains controversial. Here a water/graphite interface is investigated with high-sensitivity atomic force microscopy. We show evidence of nucleation and growth of an epitaxial monolayer on the graphite surface, probably caused by the adsorption of nitrogen molecules dissolved in water. The subsequent adsorption process resembles the layer-plus-island, or Stranski-Krastanov, growth mode in heteroepitaxy. This finding underlines the importance of gas segregation at various water interfaces and may unravel many puzzles, especially the nature and the high stability of so-called nanobubbles at solid/water interfaces and in bulk water. Based on the hydrophobic effect, we propose that gas molecules dissolved in water may aggregate into clusters in bulk water as well as at solid/water interfaces. As a cluster grows above a critical size, it undergoes a transition into a gas bubble, which can explain the formation or nucleation of gas bubbles in water.