Light scattering and fluorescence probe studies on micellar properties of Triton X-100 in KCl solutions

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Abstract
The effect of KCl on micelle formation and structure of Triton X-100 (TX-100) was investigated by using combined static and dynamic light scattering measurements, together with the fluorescence probe technique. An analysis of the light scattering data, including hydrodynamic radius and micellar aggregation number, accounted for both micelle growth and hydration. Fluorescence studies using pyrene as a probe were carried out to determine the critical micelle concentration (CMC) as a function of solution composition. In addition, with the aim of gaining information on the possible changes in the micro-environmental properties of TX-100 micelles, fluorescence probe studies, including intermolecular pyrene excimer formation and fluorescence polarization of coumarin 6 associated with micelles, were carried out. It was found that the addition of electrolyte induces a decrease in the CMC and an increase in both aggregation number and hydration. However, complementary data of partial specific volume and cloud point of the surfactant suggested that the main contribution to micellar hydration is due to water mechanically trapped in the micelle. Fluorescence measurements do not indicate changes in the micellar micropolarity, probably due to modifications of the solubilization site of the probe caused by the micellar growth. Both pyrene excimer formation and fluorescence polarization of coumarin 6 revealed an increase in microviscosity with electrolyte addition, which is consistent with increased micellar hydration.