Thermodynamic and Self-Assembly Properties of Sodium Bis(2-ethylhexyl) Sulfosuccinate in Polyethylene Glycol 200 and Water Mixed Solvent Media

The micellization behavior of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in mixed solvent media of polyethylene glycol 200 (PEG 200) and water with varying mass fractions of PEG 200 has been studied by conductivity and isothermal titration microcalorimetry (ITC) methods. The results showed that micelles existed at a certain ratio of PEG 200 in the mixed solvent. The critical micelle concentration (CMC) of AOT increased with increasing PEG 200 amount in mixed solvent, with the extent of the increase dependent on the decreased polarity and “structure-breaking effect” of the cosolvent. From the change in the Gibbs free energy of micellization (ΔGm°) relative to pure water, it was found that the systems containing a lower amount of PEG 200 (<60 wt %) had a more negative value of ΔGm°. This result confirmed that the mixed solvent with low concentration of PEG 200 was favorable for the formation of surfactant micelles, while a higher ratio of PEG 200 was unfavorable for the micellization process. The values ...