Mysteries and Emerging Understanding about Nanobubbles

Ing-Shouh Hwang^1*

¹Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:Ing-Shouh Hwang, email:ishwang@phys.sinica.edu.tw

Gas-filled nanoscale bubbles, nanobubbles, have been the focus of much attention in various research fields because of their surprising effects and many new applications. On the other hand, the study of nanobubbles is a subject of much controversy and myth. Nanobubbles have been identified at a variety of solid-water interfaces (surface nanobubbles or interfacial nanobubbles) using various techniques. Several studies also suggest existence of nanobubbles in bulk water solution (bulk nanobubbles), even though there is a lack of direct and convincing evidence for this. The basic phenomenology of nanobubbles and their existence remains unclear. According to the classical view of the air–water interface, nanobubbles should not exist at all because their small radius of curvature implies a high Laplace pressure inside the bubble that should drive gas diffusion across the interface and cause the bubbles to dissolve almost instantly. However, it has been reported that surface and bulk nanobubbles can be stable for days or longer. Explanations based on thermodynamics, kinetics, or both, have been put forward, but there is still no consensus theory of nanobubble stability. The puzzles about nanobubbles reflect our lack of fundamental understanding of the states of gas dissolved in water. I will review previous works on nanobubbles and present new experimental evidence that hopefully will lead to new understanding of gas dissolved in water in general. Puzzles about nanobubbles and other related phenomena may be resolved.

Keywords: water, gas, nanobubbles, solid-water interfaces