THERMODYNAMICS OF MICELLIZATION OF HEXADECYLTRIMETHYLAMMONIUM BROMIDE IN PROPYLENE GLYCOLWATER MIXTURE: A CONDUCTIVITY STUDY

Abstract. Micellization of hexadecyltrimethylammonium bromide (syn. cetyltrimethylammonium bromide, CTAB) in propylene glycolwater (30 % v/v) binary mixture, as well as the thermodynamic properties of the resulting micelles, were investigated by electrical conductivity measurements. The conductivity data were used to determine both the critical micellar concentration (CMC) and the micellar ionization degree () of CTAB in the temperature range 298.2310.2 K. The equilibrium model of micelle formation was applied in order to obtain the thermodynamic parameters (the standard molar Gibbs free energy, Gm 0, enthalpy, Hm 0 and entropy, Sm 0) of the micellization process. The values of Gm 0 and Hm 0 were found to be negative at all investigated temperatures, while the values of Sm 0 were positive and became more positive as temperature increased. A linear dependence between Sm 0 and Hm 0, i.e. an enthalpyentropy compensation effect, was observed. Key words: hexadecyltrimethylammonium bromide, critical micellar concentration, propylene glycolwater mixture, thermodynamics of micellization, enthalpyentropy compensation 1