Surfactant-Free Microemulsion Based on CO₂-Induced Ionic Liquids.

Area of Science:

• Green Chemistry
• Materials Science
• Colloid and Surface Chemistry

Background:

• Traditional microemulsions often rely on surfactants, which can pose environmental concerns.
• Ionic liquids (ILs) offer tunable properties but their application in microemulsions requires careful design.
• Surfactant-free systems are desirable for environmental sustainability and simplified formulation.

Purpose of the Study:

• To develop a novel surfactant-free microemulsion (SFME) utilizing carbon dioxide (CO2)-induced ionic liquids (ILs).
• To characterize the formation, microstructure, and demulsification behavior of the SFME.
• To investigate the reversible nature of the ILs for potential recycling and sustainable applications.

Main Methods:

• Synthesis of ILs by reacting dipropylamine (DPA) with CO2, forming ammonium salts and ammonium carbamate salts.
• Preparation of SFME using water (polar phase), ILs (amphi-solvent), and 1-dodecanol (nonpolar phase).
• Characterization using NMR (1H, 13C), FTIR, conductivity, pH, ternary phase diagrams, dynamic light scattering, gas chromatography, and staining methods.

Main Results:

• Successfully prepared ILs confirmed by spectroscopic and physicochemical methods.
• Established the ternary phase diagram to define single- and multiphase zones of the SFME.
• Determined the O/W (oil-in-water) microstructure of the SFME.
• Demonstrated efficient demulsification by N2 purging, removing CO2 to regenerate DPA and alter polarity, leading to phase separation.

Conclusions:

• The developed CO2-induced ILs effectively act as amphi-solvents for creating surfactant-free microemulsions.
• The SFME system exhibits tunable properties and a controllable demulsification mechanism based on CO2 removal.
• This approach offers a sustainable and recyclable alternative for microemulsion formulation and application.