Aggregation Behavior of Sodium Dioctylsulfosuccinate in Aqueous Ethylene Glycol Medium. A Case of Hydrogen Bonding between Surfactant and Solvent and Its Manifestation in the Surface Tension Isotherm

摘要

The dependence of critical micelle concentrationn(cmc) of sodium dioctylsulfosuccinate (AOT) on the amount ofnethylene glycol (EG) in water + EG medium was reported to benunusual and different from that of other surfactants to the extentnthat the cmc of AOT in EG is lower than in water. It is yet to benunderstood why AOT behaves so in water + EG medium,nalthough AOT is known to have some special properties. Hence innthe present study cmc of AOT in water + EG medium in the rangenfrom 0 to 100% (by weight) EG is measured by using surfacentension and fluorescence emission methods. In contrast to whatnwas reported, this study revealed that with respect to EG amountnthe cmc of AOT follows the general trend and AOT has higherncmc in EG than in water. On the other hand, it was surprisinglynfound that a break in the surface tension isotherm occurs in the premicellar region when the amount of EG exceeds 50%nrendering a bisigmoidal shape to the surface tension isotherm. UV spectral study showed that AOT and EG undergo hydrogennbonding in the premicellar region when the EG amount is ≥50% and this hydrogen bonding becomes less on adding NaCl. Thendensity functional theory calculations also showed formation of hydrogen bonds between EG and AOT through the sulfonatengroup of AOT providing thereby support to the experimental findings. The calculations predicted a highly stable AOT-EG-H2Ontrimer complex with a binding energy of −37.93 kcal mol−1. The present system is an example, which is first of its kind, of a casenwhere hydrogen bonding with surfactant and solvent molecules results in a surface tension break