Detection of novel gaseous states at the highly oriented pyrolytic graphite-water interface

We report a novel form of the gaseous state at the interface of water and highly oriented pyrolytic graphite (HOPG) that is induced by local supersaturation of gas. Such local supersaturation of gas next to the HOPG substrate can be achieved by (1) displacing an organic liquid with a gentle flow of water, (2) displacing cold water (approximately 0 degrees C) with a gentle flow of warm water (approximately 40 degrees C), or (3) preheating the HOPG substrate to approximately 80 degrees C before exposing it to water at room temperature. In addition to the spherical-cap-shaped nanobubbles reported by many researchers, flat (quasi-two-dimensional, pancake-like) gas layers and nanobubble-flat gas layer composites (spherical-cap-shaped nanobubbles sitting on top of the quasi-two-dimensional gas layers) were detected. These entities disappeared after the system was subjected to a moderate level of degassing (approximately 0.1 atm for 1.5 h), and they did not form when the liquids involved in the aforementioned displacing procedure (to induce local supersaturation of gas) had been predegassed (to approximately 0.1 atm). The stability and some physical properties of these newly found gaseous states are examined.