Coalescence, Growth, and Stability of Surface-Attached Nanobubbles

Surface-attached nanobubbles once formed and kept under constant conditions Show remarkable stability against dissolution. When observing a large population of nanobubbles using total internal reflection fluorescence (TIRF), microscopy, we find rare events of coalescence, i.e., the merging of two neighboring bubbles. The new bubble covers the convex hull of their footprint, with most of the three-phase contact line remaining pinned. Interestingly, the newly formed bubble is not shape-stable but grows in height within several 100 ms. This growth dynamic can be described with the classical diffusion theory using contact line pinning and Henry's law. This theory also shows that surface nanobubbles can attain a stable shape with a contact angle larger than 90 in supersaturated liquid.