Surface nanobubbles are tiny gas pockets with nanoscale thickness, situated at the solid-liquid interface. Initially considered as impurities in the liquid or artifacts resulting from interactions with the surface and the tip of the Atomic Force Microscope, their unexpected longevity has challenged these assumptions. While traditional nano-sized bubbles were expected to dissolve within microseconds according to the Epstein-Plesset relation, nanobubbles have been observed to persist for days in experiments. Notably, they can withstand the removal of up to 80% of gas from the surrounding liquid.

These unusual properties of nanobubbles have led to various explanations regarding their stability. The most recent proposition attributes the prolonged lifespan of surface nanobubbles to the impact of the substrate potential on the diffusion dynamics of gas molecules. However, this presents a challenge, as the binding energy of a gas molecule with the surface reduces in the presence of the solvent. Consequently, an alternative mechanism must be at play to stabilize the nanobubble under these conditions.

In the initial phase of this study, we employed molecular dynamics simulations to explore the accumulation of gas in various forms at the graphene-water interface. Our findings indicate that gas molecules can move across a solid surface, aggregating to form a surface nanobubble with distinct morphological features. The process of gas adsorption on surfaces, especially in the presence of a solvent, is significantly influenced by the wetting characteristics of the solid.

In the second part of our study, our observations reveal that, with a conventional nitrogen-graphene interaction energy of 3.39kT, gas molecules escape from the surface within 250ns, and the resulting bubble dissolves within 300ns. Consequently, the hypothesis suggesting that the stability of the nanobubble is due to hydrophobic interaction proves to be incorrect.

Finally we explore a possible mechanism of ion accumulation at the gas-water interface and its effect on the lifetime of surface nanobubble.