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 ΔH m° 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.

Effect of Compressed CO2 on the Critical Micelle Concentration and Aggregation Number of AOT Reverse Micelles in Isooctane

“…As an example, Figure 2 shows the dependence of the differential signal of UV absorbance (DA/DC, where A and C are the UV absorbance and the concentration of AOT) of tert-butylphenol (tBP) in AOT/isooctane on the AOT concentration at 308.2 K in the absence of CO 2 . The shape of the curve is similar to that reported by Murali Manoj et al [44] The plot of absorbance of tBP at maximum absorption (l max ) shows a discontinuous and abrupt change at the cmc value, where DA/DC is zero. [a] The data in parentheses are those reported in reference [44].…”

“…The shape of the curve is similar to that reported by Murali Manoj et al [44] The plot of absorbance of tBP at maximum absorption (l max ) shows a discontinuous and abrupt change at the cmc value, where DA/DC is zero. [a] The data in parentheses are those reported in reference [44].…”

“…The data determined by Mutelet et al [43] are also shown in the Fig Critical micelle concentration: UV/Vis spectroscopy is a useful technique to determine the cmc value. [44][45][46] In this work, the cmc values of AOT were measured by this method. As an example, Figure 2 shows the dependence of the differential signal of UV absorbance (DA/DC, where A and C are the UV absorbance and the concentration of AOT) of tert-butylphenol (tBP) in AOT/isooctane on the AOT concentration at 308.2 K in the absence of CO 2 .…”

“…[44,[47][48][49][50] Many fluorescence studies of AOT/oil reverse micelles in the absence of CO 2 have been reported. [44,[47][48][49][50] To measure the aggregation number of the AOT/ isooctane system, 8-anilinol-1-naphthalenesulfonic acid (ANS) is used as the probe and N-cetylpyridinium chloride (CPC) is used as the quencher. As an example, Figure 6 a shows the dependence of the fluorescence spectra of ANS The aggregation number in CO 2 -free reverse micelles determined by fluorescence quenching is 125, which agrees with the result reported by other authors.…”

“…As an example, Figure 6 a shows the dependence of the fluorescence spectra of ANS The aggregation number in CO 2 -free reverse micelles determined by fluorescence quenching is 125, which agrees with the result reported by other authors. [44] We also determined the aggregation numbers of AOT reverse micelles in isooctane at 303.2 K and with different mole fractions of CO 2 ; the results are listed in Table 2. It can be observed that the aggregation number also has a maximum at about X CO 2 = 0.40.…”