Determination of enthalpy and entropy of micellization for Brij-35 and the Effect of salts on critical micellar concentration

Abstract

In this study the thermodynamic parameters of micelle formation for Brij-35 (the nonionic polyoxyethylene ether surfactants Brij 35 (C12E23 i.e. CH3(CH2)11(OCH2CH2)23OH) will be determined from kinetics data. The reaction used is the reduction of m-chloroperbenzoic acid by iodide. The initial concentrations of peracid and iodide were 4 x 10-6 M and 1.5 x 10-3 M respectively. Reactions were carried out in 0.003 M nitric acid and in presence of sodium sulphate and sodium perchlorate. .The results show that, the Hydrophilic ―salting out‖ sulphate ions increase the rate constant of the reaction in the micelle and reduce the critical micellar concentration (CMC); whereas hydrophobic ―salting in‖ ions perchlorate decrease the rate constant and have much less effect on the CMC. In all different conditions investigated the temperature seems to increase the rate and decrease the critical micelle concentrations.