Understanding the stability and properties of bulk nanobubbles

The existence of bubbles in the nanoscale is an object of debates and disputes in recent years. New types of nanoscale bubble systems have been reported, and among these, Bulk Nanobubbles represent a challenging problem due to their extraordinary stability experimental reported. In pure water, the pressure estimated from the Young-Laplace equation inside a nanobubble of 100 nm diameter will be close to ~30 atm, therefore, questions of their existence/ stability inevitably arise considering that the lifetime of macrobubbles (>1 mm) is on the order of minutes and that of microbubbles (1-1000 µm) is on the order of seconds, whereas bulk nanobubbles (50-300 nm) have been reported to last for days or weeks. Bulk nanobubbles have a higher curvature leading to a higher Laplace pressure, and a larger interfacial area for gas to diffuse out and it should be in principle less stable. Reports stated that they are negatively charged, and speculations arise on the stability mechanism that could affect their stability against the bubble dissolution theories. Bulk nanobubbles are recent, and their research is still in its infancy; however, many applications have been reported and tested, and it appears that there is immense scope for nanobubbles to impact and perhaps revolutionise many current industrial sectors and medical processes.