Thermodynamic and aggregation behavior of mixed micellar systems of sodium decanoate and ethoxylated alcohols in water at 25°C

Densities and ultrasonic velocities of binary aqueous systems of sodium decanoate (C10Na), of a medium chain length alkoxyethanol with varying number of ethylene oxide groups (C4EO0-3), and of ternary systems of these compounds have been measured as a function of surfactant and alcohol concentrations at 25°C. The derived apparent molar volume and molar adiabatic compressibility properties of C10Na in water were fitted with a mass-action model to obtain the thermodynamic micellization parameters of C10Na. The infinite dilution transfer molar volume and transfer molar adiabatic compressibility properties of C4EO0-3 from water to aqueous C10Na solutions were obtained from the corresponding apparent molar properties using a chemical equilibrium model. The results of simulating the experimental transfer function data of these alcohols at a given low concentration of 0.05mA show that the solubilization of C4EO0-3 compounds in C10Na micelles is enhanced by increasing the number of ethylene oxide groups (EO) in the alcohol. The mean aggregation number of C10Na, which is 34 in the absence of alcohol, remains unchanged in the presence of 0.05mA while the average number of alcohol molecules per micelle increases steadily as a function of the number of EO groups in the alcohol.