Mechanistic insights into nanobubbles dynamics through in-situ liquid phase electron microscopy*

The observation of surface nanobubbles at real-time scales is essential to understand the interactions between their adjacencies. Therefore, to gain insights into their dynamic behavior, we used in-situ liquid-phase electron microscopy technique to observe surface nanobubbles with high spatial and temporal resolutions. A water film, having thickness of hundreds of nanometers, was encapsulated between two silicon nitride membranes and was observed using a 200 kV transmission electron microscope. The gas nanobubbles were nucleated by radiolysis phenomenon, which creates the locally gas oversaturated environment in the liquid. Our study focuses on the pinning-depinning characteristics of nanobubbles' contact line and the coalescence following contact line depinning. The differential gas oversaturation around a strongly pinned gas nanobubble leads to the asymmetric and directional depinning of its contact line. Further, we found that the two nanobubble coalescence is initiated by the formation of an adsorbed gas layer between the nanobubbles' adjacent contact line, which also acts as a bridge for gas exchange. Overall, our experimental investigation shows that the gas oversaturation is dominant in governing the studied nanobubble dynamics.