Water/supercritical CO2 microemulsions with mixed surfactant systems

Area of Science:

• Physical Chemistry
• Materials Science
• Colloid and Surface Chemistry

Background:

• Water/supercritical CO2 (W/scCO2) microemulsions are crucial for various applications.
• Stabilization of these microemulsions often involves complex surfactant systems.
• Understanding phase behavior and stability is key to optimizing microemulsion performance.

Purpose of the Study:

• To investigate the phase behavior of W/scCO2 microemulsions stabilized by sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2) mixed with guest surfactants.
• To evaluate the impact of fluorocarbon-hydrocarbon hybrid anionic surfactants (FC6-HCn) on microemulsion stability and water solubilization.
• To elucidate the molecular packing and interfacial properties influencing microemulsion stability.

Main Methods:

• Phase behavior investigation of W/scCO2 microemulsions.
• Fourier transform infrared (FT-IR) spectroscopy to analyze phase transitions.
• Interfacial tension measurements for W/scCO2 systems.

Main Results:

• Mixing 8FS(EO)2 with FC6-HCn surfactants resulted in a higher maximum water-to-surfactant molar ratio (W0(c)) than predicted by linear interpolation.
• FT-IR measurements indicated that the surfactant mixtures prevented phase transitions to liquid crystals, even with excess water.
• Interfacial tension measurements showed increased area per surfactant molecule upon mixing, suggesting looser molecular packing.

Conclusions:

• The addition of fluorocarbon-hydrocarbon hybrid surfactants (FC6-HCn) significantly enhances the stability of W/scCO2 microemulsions.
• Microsegregation of 8FS(EO)2 and FC6-HCn likely leads to loose molecular packing and improved microemulsion stability.
• These findings offer a pathway to design more robust and efficient W/scCO2 microemulsion systems.