Physicochemical Studies on Reverse Micelles of Sodium Bis(2-ethylhexyl) Sulfosuccinate at Low Water Content

Abstract

Studies on aggregation of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in isooctane at low water content were carried out. The critical micelle concentration (cmc) thermodynamic parameters were determined at various temperatures. The observations suggested that the micellization process was endothermic in nature and that it is mainly an entropic process. The cmc was also determined at various R values (R < 3) and it was found that cmc increases with increasing R. The aggregation number was determined at the R value of 1.6. From the pyrene and ANS binding studies, the microviscosity and micropolarity changes on the onset of micellization are well characterized. Spectral studies with ANS indicate a decrease in microviscosity on increase in R value. ANS fluorescence was monitored in the presence of additives like acrylamide, KI3, and tetrabutylammonium iodide. The iodide-based additives lead to quenching of fluorescence of ANS with concomitant red shift in the λem suggesting decreased microviscosity and micropolarity. Acrylamide was shown to increase the polarity by the ANS spectral features. These findings led to the conclusions that the positive ΔHm° values arise mainly from the dismantling of hydrated ions in the quasi-lattice of AOT interior. With an increase in temperature, immobilized structured states of water get destructured, which ultimately leads to favoring the aggregation process.