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Thermodynamic and Self-Assembly Properties of Sodium Bis(2-ethylhexyl) Sulfosuccinate in Polyethylene Glycol 200 and Water Mixed Solvent Media
journal contribution
posted on 2018-12-07, 21:44 authored by Sha Li, Mengzhen Ye, Meng Han, Qian Zhang, Min Liu, Jie Liu, Dezhi SunThe 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 of the other two thermodynamic
parameters (ΔHm° and −TΔSm°) indicated that the micelle formation was entirely entropy driven
for the systems with pure water or high content of PEG 200 (≥80
wt %). The other systems were driven by entropic as well as enthalpic
contributions. There are complex factors involved in the effect of
mixed solvent composition on the energetics of micelle formation.
The polarity, dielectric constant, polymer concentration, and position
of the added polymer in the micelle may be worth considering for understanding
the self-assembly behavior of the surfactant. In addition, the self-assembly
behaviors of AOT in ethylene glycol (EG)/water and PEG 400/water were
studied and compared. It was found that the variation trend of the
parameters showed a similarity, but there are subtle differences between
the three systems.