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Control of Ostwald ripening by using surfactants with high surface modulus
Slavka Tcholakova1, Zlatina Mitrinova, Konstantin Golemanov
1Department of Chemical Engineering, Faculty of Chemistry, Sofia University, 1 J. Bourchier Avenue, 1164 Sofia, Bulgaria. SC@LCPE.UNI-SOFIA.BG
Langmuir : the ACS Journal of Surfaces and Colloids
|November 9, 2011
Summary
Surfactant properties and glycerol significantly influence bubble coarsening in foams. High surface modulus surfactants and glycerol slow down Ostwald ripening by reducing gas permeability through foam films.
Area of Science:
- Colloid and Surface Science
- Materials Science
- Fluid Dynamics
Background:
- Ostwald ripening is a key destabilization process in foams, driven by gas diffusion between bubbles.
- Understanding factors affecting Ostwald ripening is crucial for foam stability in various applications.
Purpose of the Study:
- To systematically investigate the rate of bubble Ostwald ripening in concentrated foams (90% air volume fraction).
- To elucidate the role of surfactant properties and aqueous phase composition on gas permeability and foam coarsening.
- To validate a new theoretical model for foam film permeability.
Main Methods:
- Systematic measurements of Ostwald ripening rates in foams with varying surfactant systems (high/low surface modulus) and glycerol concentrations.
- Utilizing the diminishing bubble method for independent verification of gas permeability measurements.
- Employing Langmuir trough experiments to assess surface tension dynamics.
Main Results:
- Foams with high surface modulus surfactants exhibited significantly slower Ostwald ripening due to reduced gas permeability of adsorption layers.
- Glycerol addition decreased gas solubility and diffusivity in the aqueous core, also slowing Ostwald ripening.
- A new theoretical model successfully determined foam film gas permeability, distinguishing contributions from adsorption layers and aqueous core.
Conclusions:
- The rate of Ostwald ripening in foams is primarily governed by the gas permeability of surfactant adsorption layers and the aqueous core.
- High surface modulus surfactants and glycerol effectively reduce Ostwald ripening rates by impeding gas diffusion.
- The developed theoretical model provides accurate predictions of foam film permeability, validated by experimental data.
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