Stable nanobubbles on ordered water monolayer near ionic model surfaces

The stable nanobubbles adhered to mineral surfaces may facilitate their efficient separation via flotation in the mining industry. However, the state of nanobubbles on mineral solid surfaces is still elusive. In this study, molecular dynamics（MD） simulations are employed to examine mineral-like model surfaces with varying degrees of hydrophobicity, modulated by surface charges, to elucidate the adsorption behavior of nanobubbles at the interface. Our findings not only contribute to the fundamental understanding of nanobubbles but also have potential applications in the mining industry. We observed that as the surface charge increases, the contact angle of the nanobubbles increases accordingly with shape transformation from a pancake-like gas film to a cap-like shape, and ultimately forming a stable nanobubble upon an ordered water monolayer.When the solid–water interactions are weak with a small partial charge, the hydrophobic gas（N2） molecules accumulate near the solid surfaces. However, we have found, for the first time, that gas molecules assemble a nanobubble on the water monolayer adjacent to the solid surfaces with large partial charges. Such phenomena are attributed to the formation of a hydrophobic water monolayer with a hydrogen bond network structure near the surface.