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Issue 47, 2018
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Interpreting the interfacial and colloidal stability of bulk nanobubbles

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Abstract

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

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Publication details

The article was received on 24 Sep 2018, accepted on 10 Nov 2018 and first published on 12 Nov 2018


Article type: Paper
DOI: 10.1039/C8SM01949E
Citation: Soft Matter, 2018,14, 9643-9656
  • Open access: Creative Commons BY license
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    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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