Nanoscale gas accumulation at solid-liquid interfaces: a molecular dynamics study

The development of the interfacial gas enrichment layer at the solid-liquid interface is coupled with the stability of surface nanobubbles. Depending upon the concentration of gas molecules, solid-liquid-gas interaction strengths, and other thermodynamic parameters, gas molecules can take several different forms such as dense gas layer, bulk and surface nanobubble, and other gaseous domains. Using molecular dynamics simulations we study the characteristics of gas accumulation into a dense gas layer, surface nanobubble and local gas aggregation at the graphene-water interface with no pinning sites. We find that gas molecules can migrate over the solid surface and can collect together to take the morphological form of a surface nanobubble. The developed nanobubble is mobile and can move over the homogeneous hydrophobic solid surface without losing its shape. We find that the gas adsorption on surfaces in the presence of a solvent is strongly affected by the wetting characteristics of the solid. In the absence of a solvent, gas adsorption is found to be universal for all surface types. Individual gas adsorption is found to be prominent and occurs in a short period, and is essential for the stability of the formed gaseous domains. Simulation results show gas adsorption density on surfaces to have a strong dependence on the solid-liquid interaction parameter than on solid-gas interaction strength.