Apparent Molar Volume and Apparent Molar Adiabatic Compressibility Studies of 2,6-Di- tert-butyl-4-methylphenol and 2- tert-Butyl-4-methoxyphenol in Aqueous Micelle Solutions of Hexadecyltrimethylammonium Chloride as a Function of Surfactant Concentration and Temperature

Abstract

Ultrasonic velocities and densities of aqueous solutions of cetyltrimethylammonium chloride have been measured at concentrations below 0.35 mol kg -1 at 25, 35, and 45°C. Apparent molar volume and apparent molar adiabatic compressibility properties of the aqueous surfactant solutions were derived from these data. Apparent molar volumes and apparent molar adiabatic compressibilities of 2,6-di- tert-butyl-4-methylphenol and 2- tert-butyl-4-methoxyphenol dissolved in aqueous micellar solutions of cetyltrimethylammonium chloride were determined as a function of surfactant concentration and temperature. The results obtained for the binary and ternary systems are compared with those previously published for binary aqueous cetyltrimethylammonium bromide systems and for ternary systems of this surfactant containing the same additives. The degree of counterion dissociation from the micelles and the effect this has on the extent of hydration of the head group region of the micelle are shown to have an effect on the solubilization sites of hydrophobic-like additives in these micelles.