A thermometric titration study on the micelle formation of sodium decyl sulfate in water

The critical micelle concentration (cmc) and the enthalpy of micelle formation (Delta H-mic) of sodium n-decyl sulfate (SDeS) in aqueous solutions were determined in the temperature range 15-45 degreesC by isothermal titration microcalorimetry. An empirical sigmoidal expression providing high accuracy and internal consistency was used for the evaluation of the titration curves. As a function of increasing temperature, the cmc passes through a minimum at 29.5 degreesC, where Delta H-mic changes sign from positive to negative. The isosteric enthalpies calculated by means of the van't Hoff relation agree very well with the directly measured calorimetric enthalpies. The emc, enthalpy, Gibbs energy, entropy, and heat capacity data of SDeS micellization are reported and compared with the results of previous studies on the same system. It was found that the presence of n-decanol, which appears to be a product of the natural hydrolysis of SDeS, significantly lowers the cmc. Delta H-mic is less appreciably influenced by this impurity. (C) 2001 Academic Press.