Dynamic behavior of near-surface nanobubbles formation and development

• The formation and development of nanobubbles near the solid surface were studied. • The effects of bubble size and bubble spacing on bubble coalescence were revealed. • The influence of wettability on the formation and development of surface nanobubbles was introduced. In this work, the molecular dynamics simulation was employed to study the formation and development mechanisms of near-surface nanobubbles, especially, the effects of wettability on the dynamic behaviors of nanobubbles was exhibited and analyzed. The results show that there are nanobubbles in the evolution process, as well as a gas-enriched layer in the system. The formation of nanobubbles can be divided into two stages, i.e., the initial stage and steady stage, according to the change of kinetic energy. Then, it is indicated that wettability has obvious effects on the formation of nanobubbles. In the coalescence process of nanobubbles, the vapor molecules in small bubbles could actively move into the large ones leading to the continuous change of the shape of the coalesced bubbles. Finally, the hydrophobic wall is found more favorable to gaseous molecules, which makes it easier to form surface nanobubbles. This work provides the theoretical guidance for further practical application of near-surface nanobubbles.