On the clustering of bulk nanobubbles and their colloidal stability

Bulk nanobubbles which are usually observed in pure water have a mean diameter typically around 100 nm. We use a combination of physical and chemical techniques to prove the hypothesis that the nanoentities observed in pure water are stable clusters of much smaller stable nanobubbles. The stability of bulk nanobubble clusters is affected by factors such as ionic strength or internal energy of the system. We show that bulk nanobubbles on the order of 100 nm exist in a stable cluster form in neutral or basic media, and dissociate into tiny primary nanobubbles on the order of 1 nm in acidic media, or in the presence of small amounts of salt. These new findings suggest that bulk nanobubbles which have a high surface energy unsurprisingly tend to behave in a similar manner to solid nanoparticles in terms of their agglomeration tendency, which is confirmed by the DLVO theory. The results will have important implications for our understanding and interpretation of the behaviour of bulk nanobubbles, in particular their interfacial and colloidal stability. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

Bulk nanobubbles, with an average diameter of around 100 nm, form stable clusters in pure water and exhibit different stability in different media. The study reveals that bulk nanobubbles tend to behave similarly to solid nanoparticles in terms of agglomeration tendency, which has significant implications for our understanding of their behavior and stability.