The Effect of Organic Additives on the Thermodynamic Parameters of Micellization

Abstract

Abstract The CMC values of dodecylammonium chloride and iodide and of hexadecylammonium chloride were measured in water upon the addition of acetone, 1-propanol, and urea at several temperatures. The effects of the additives were most remarkable on the CMC of hexadecylammonium chloride at 45.0 °C. Urea was less effective on the disruption of micelles than acetone, while the addition of 1-propanol was most effective. The enthalpy of micellization became more negative, while the entropy of micellization became less positive, as the additive concentration increased. We divided the standard free energy of micellization into the hydrophobic term, ΔG°n, and the hydrophilic term, ΔG°p. The value of ΔG°p became more negative with the additive concentration and contributed to the stabilization of the micelle, while ΔG°n became less negative. Therefore, it was concluded that the disruption of the micelle in the presence of these organic additives results from an increase in the free energy in the hydrophobic group of the surfactant molecule.