Thermodynamic and aggregation properties of sodium n-hexylsulfonate in aqueous solution

Thermodynamic and aggregation properties of sodium n-hexylsulfonate (C6H13SO3Na) in aqueous solutions have been studied at different temperatures by density, sound velocity, electroconductivity and vapor–liquid equilibria measurements. The critical micelle concentration (CMC), counterion binding of micelles and thermodynamics of micellization have been evaluated. From the density and sound velocity data, the values of the apparent molar volumes and compressibilities, changes in the apparent molar properties upon micellization and the infinite dilution apparent molar properties of the monomer state of C6H13SO3Na in the aqueous solutions were determined. Vapor–liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through the isopiestic method. A comparison between the mentioned thermodynamic and aggregation properties of C6H13SO3Na in aqueous solutions with those of some other sodium n-alkylsulfonates were also made and from which the effect of the alkyl chain length of the surfactant on the aggregation parameters were examined.