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Interpreting the interfacial and colloidal stability of bulk nanobubbles
N Nirmalkar1, A W Pacek, M Barigou
1School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. m.barigou@bham.ac.uk.
Soft Matter
|November 21, 2018
Summary
Stable bulk nanobubbles in pure water are maintained by a charged interface and colloidal forces. Adjusting pH and avoiding salts enhances nanobubble longevity, while surfactants have varied effects.
Area of Science:
- Colloid and Surface Science
- Nanotechnology
- Physical Chemistry
Background:
- Bulk nanobubbles present a novel system with poorly understood stability mechanisms.
- Understanding nanobubble stability is crucial for their application in various fields.
Purpose of the Study:
- To elucidate the interfacial and colloidal stability of bulk nanobubbles in pure water.
- To investigate the influence of pH, salts, and surfactants on nanobubble suspension stability.
Main Methods:
- Generation of stable bulk nanobubble suspensions using hydrodynamic cavitation in a microfluidic device.
- Systematic study of the effects of pH, ionic strength (salts), and surfactant types on nanobubble stability.
- Application of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for colloidal stability analysis.
Main Results:
- Nanobubble interfaces in pure water exhibit a negative charge, forming an electric double layer that counteracts Laplace pressure, ensuring stability.
- Stability increases with higher alkalinity; addition of mono- and multi-valent salts screens the electric double layer, leading to destabilization.
- Different surfactant types (non-ionic, anionic, cationic) demonstrate varied impacts on nanobubble stability.
Conclusions:
- The long-term stability of bulk nanobubbles in pure water is attributed to a combination of interfacial ion stabilization against dissolution and overall colloidal stability.
- The charged interface and electrostatic repulsion, as predicted by DLVO theory, are key factors in maintaining stable nanobubble suspensions.
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