Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 47, Pages 25143-25150Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202110091
Keywords
emulsions; sum frequency generation (SFG) spectroscopy; surface analysis; surface tension; surfactants
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Funding
- BASF SE, Ludwigshafen
- Projekt DEAL
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This study used surface-sensitive SFG spectroscopy to demonstrate that the adsorption of surfactants to the oil/water interface increases the interfacial electric field and enhances the ordering of interfacial oil molecules. At high surfactant concentrations, the interfacial charge peaks and the interfacial oil molecules arrange in a fully ordered conformation, leading to decreased interfacial tension and increased emulsion stability.
The oil/water interface, for instance in emulsions, is often stabilized by surfactants. Hence, the co-existence of oil, water, and surfactant molecules at the buried oil/water interface determines macroscopic properties such as surface tension or emulsion stability. Utilizing an inherently surface sensitive spectroscopic method, sum frequency generation (SFG) spectroscopy, we show that adsorption of an anionic surfactant to the buried oil/water interface increases the magnitude of the interfacial electric field. Meanwhile, the degree of ordering of the interfacial oil molecules increases with the surfactant concentration owing to the intercalation of aliphatic chains of interfacial oil and surfactant molecules. At sufficiently high surfactant concentrations, the interfacial charge reaches a maximum value and the interfacial oil molecules arrange in a fully ordered conformation, a state which coincides with the significant decrease in interfacial tension and increased emulsion stability.
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