Issue 47, 2018

Interpreting the interfacial and colloidal stability of bulk nanobubbles


This paper elucidates parts of the mystery behind the interfacial and colloidal stability of the novel bubble system of bulk nanobubbles. Stable bulk nanobubble suspensions have been generated in pure water using hydrodynamic cavitation in a high-pressure microfluidic device. The effects of pH adjustment, addition of different types of surfactant molecules and salts on the nanobubble suspensions have been studied. Results show that nanobubble interfaces in pure water are negatively charged, suggesting the formation of an electric double layer around the nanobubbles. It is presumed that the external electrostatic pressure created by the charged nanobubble interface, balances the internal Laplace pressure; therefore, no net diffusion of gas occurs at equilibrium and the nanobubbles are stable. Such stability increases with increasing alkalinity of the suspending medium. The addition of mono- and multi-valent salts leads to the screening of the electric double layer, hence, destabilizing the nanobubbles. Different surfactant molecules (non-ionic, anionic, cationic) affect the stability of bulk nanobubbles in different ways. Calculations based on the DLVO theory predict a stable colloidal system for bulk nanobubbles in pure water and this could be a further reason for their observed longevity. All in all, in pure water, the long-term stability of bulk nanobubbles seems to be caused by a combination of ion-stabilisation of their interface against dissolution and colloidal stability of the suspension.

Graphical abstract: Interpreting the interfacial and colloidal stability of bulk nanobubbles

Article information

Article type
24 Sep 2018
10 Nov 2018
First published
12 Nov 2018
This article is Open Access
Creative Commons BY license

Soft Matter, 2018,14, 9643-9656

Interpreting the interfacial and colloidal stability of bulk nanobubbles

N. Nirmalkar, A. W. Pacek and M. Barigou, Soft Matter, 2018, 14, 9643 DOI: 10.1039/C8SM01949E

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