Enhanced stabilization of reverse micelles by compressed CO2

Area of Science:

• Physical Chemistry
• Colloid and Surface Chemistry
• Supramolecular Chemistry

Background:

• Reverse micelles are self-assembled aggregates of surfactants in nonpolar solvents.
• Sodium bis(2-ethylhexyl) sulfosuccinate (AOT) is a common surfactant used to form reverse micelles.
• Understanding the behavior of reverse micelles is crucial for applications in solubilization and reaction media.

Purpose of the Study:

• To investigate the effect of compressed carbon dioxide (CO2) on the water solubilization capacity of AOT reverse micelles.
• To determine the optimal CO2 pressure range for enhanced water solubilization.
• To elucidate the mechanism of CO2-induced stabilization of reverse micelles.

Main Methods:

• Studying the solubilization of water in AOT reverse micelles in n-alkanes under varying temperatures and pressures.
• Utilizing UV/Vis adsorption spectroscopy with methyl orange (MO) as a probe to investigate microenvironments.
• Analyzing the influence of CO2 pressure and water-to-AOT molar ratio (W0) on micellar properties.

Main Results:

• Compressed CO2 significantly increases water solubilization within a specific pressure range.
• The optimal CO2 pressure for enhanced solubilization decreases as the W0 increases.
• CO2 stabilizes reverse micelles by increasing interfacial rigidity, attributed to its smaller molecular volume compared to n-alkanes.
• Excessively high CO2 pressure reduces solvent strength, leading to phase separation.

Conclusions:

• Compressed CO2 is an effective agent for enhancing water solubilization in AOT reverse micellar systems.
• The interaction of CO2 with the micellar interface plays a key role in stabilization.
• Careful control of CO2 pressure is necessary to avoid detrimental effects like phase separation.