Surface Nanobubble Nucleation Visualized with TIRF Microscopy

Nanobubbles are observed with optical microscopy using the total internal reflection fluorescence (TIRF) excitation. We report on TIRF visualization using Rhodamine 6G at 5$μ\,$M concentration which results to strongly contrasted pictures. The preferential absorption and the high spatial resolution allow to detect nanobubbles with diameters of 230\,nm and above. We present a study of the nucleation dynamics from the water-ethanol-water exchange and report the size distributions. Nanobubble nucleation is observed within 4 min after the exchange, later a stable population of nanobubbles with a surface density of 0.55 bubbles\,/$μ$m$^2$ is formed. Interestingly, unstable, slowly dissolving nanobubbles are observed during the first stage of water-ethanol exchange; only after the ethanol-water exchange stable nanobubbles appear.

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