Effect of temperature on aggregation behavior of aqueous solutions of sodium cumene sulfonate

Aqueous solutions of sodium cumene sulfonate are characterized by various experimental techniques for its aggregation behavior as a function of temperature. Surface tensiometry, volumetric changes, vapor pressure osmometry, fluorescence polarization studies and enthalpy changes show changes in the solutions with increasing concentration and temperature. The apparent and partial molal volumes of the hydrotrope, derived from the density measurements, show a sharp increase at a characteristic minimum hydrotrope concentration. The osmotic coefficient of NaCS, obtained from vapor pressure osmometry, shows a significant deviation indicating aggregation of the hydrotrope molecules in aqueous solutions. NaCS, when used as an intrinsic fluorescent probe, reveals a non-polar environment in the aggregate with substantial microviscosity. The enthalpies of micellization obtained directly from the calorimetric measurements show a trend towards lower values with increasing temperature.