Molecular dynamics simulation of CO₂-switchable surfactant regulated reversible emulsification/demulsification...

Area of Science:

• Physical Chemistry
• Materials Science
• Colloid and Surface Science

Background:

• CO2-switchable surfactants offer tunable control over emulsion stabilization and destabilization.
• Understanding the molecular mechanisms governing their reversible action is crucial for industrial applications.

Purpose of the Study:

• To elucidate the fundamental mechanism behind the reversible emulsification/demulsification by a CO2-switchable surfactant.
• To investigate the role of molecular interactions in the switching behavior of N'-dodecyl-N,N-dimethylacetamidinium (DMAAH+) and N '-dodecyl-N,N-dimethylacetamidine (DMAA).

Main Methods:

• Molecular dynamics simulations were employed to study a dodecane-saline system with the CO2-switchable surfactant.
• Analysis included density profiles, interfacial tension, hydrogen bonding, and Lennard Jones and coulombic potentials.

Main Results:

• DMAAH+ significantly increased oil-water interfacial thickness and sharply reduced interfacial tension compared to DMAA.
• Hydrogen bonds alone were insufficient to explain the CO2-switchability; coulombic interactions were identified as critical.
• Enhanced coulombic interactions between DMAAH+ and water/anions were responsible for reduced interfacial tension and emulsification.

Conclusions:

• Coulombic interactions are the primary driving force for the reversible emulsification/demulsification processes mediated by DMAAH+/DMAA.
• This finding provides fundamental insights into designing and utilizing CO2-switchable surfactants for advanced applications.