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Salt effects in surfactant-free microemulsions.
Sebastian Schöttl1, Dominik Horinek1
1Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
The Journal of Chemical Physics
|June 17, 2018
Summary
Adding salts like sodium iodide and lithium chloride to water/ethanol/1-octanol microemulsions alters aggregate structure. Ethanol concentrates at the interface, weakening charge separation and ion adsorption.
Area of Science:
- Physical Chemistry
- Colloid and Surface Science
Background:
- Surfactant-free microemulsions, particularly in the "pre-ouzo region", exhibit complex micellar aggregates.
- These aggregates are sensitive to compositional changes and the addition of salts.
Purpose of the Study:
- To investigate the impact of sodium iodide and lithium chloride on the structure of micellar aggregates in water/ethanol/1-octanol microemulsions.
- To understand the molecular mechanisms behind salt-induced changes.
Main Methods:
- Molecular dynamics simulations were employed to model the microemulsion system.
- Analysis focused on the distribution of components and interfacial properties.
Main Results:
- Both salts induced a salting-out effect, increasing ethanol concentration in the nonpolar phase and at the interface.
- A minor interface charging occurred due to differential ion adsorption, but was mitigated by the aggregate surface structure.
- Ethanol at the interface shielded hydrophobic regions, reducing preferential adsorption of iodide and lithium ions.
Conclusions:
- Salts significantly influence the structure and interfacial properties of these surfactant-free microemulsions.
- The interplay between ethanol, ions, and the aggregate surface dictates the observed changes.
