Research progress on bulk nanobubbles

There are still fundamental problems lying in the basic research of bulk nanobubbles. Are the bulk nanobubbles reported in the literature nano scale bubbles or contaminants in fact? At present, there is not yet sufficient experimental evidence to show that the bulk nanoparticles are only gas bubbles but not other nano scale contaminants. If they are indeed nanobubbles, what causes the bulk nanobubbles observed in the literature to be much more stable than being predicted by the Epstein-Plesset theory? This paper firstly discusses the contradiction between the traditional theory prediction and the observed lifetime of the bulk nanobubbles, and then discusses whether the so-called nanobubbles are gas aggregates. We review the existing typical models, and the influence of different conditions on the stability of bulk nanobubbles, for paving the road to a clear understanding of the stability mechanism of bulk nanobubbles. In addition, the representative production methods and characterization methods of bulk nanobubbles are discussed in order to offer some guidance to their wide range of commercial applications. (c) 2021 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

There are still fundamental problems in the basic research of bulk nanobubbles, including whether they are truly nanoscale bubbles or contaminants, and the stability mechanism that differs from the Epstein-Plesset theory. This paper discusses the contradiction between traditional theory predictions and observed lifetimes of bulk nanobubbles, examines the possibility of gas aggregates, and reviews existing models and conditions that influence their stability. Additionally, it provides guidance on production and characterization methods for the wide range of commercial applications of bulk nanobubbles.