In this work, we observed that there are distinct differences between C12SO3Na and C12SO4Na with respect to the interaction with PEG, based on the measurements of volumetric, compressibility and electrical conductivity. The concentration dependence of the all investigated thermodynamic properties exhibit a change in slope at the concentration in which micelles are formed. The effect of temperature and concentration of PEG on the critical micelle concentration (CMC) of both C12SO3Na and C12SO4Na in aqueous solution has been investigated. The values of the Gibbs free energy of micelle formation ( ) for both surfactant in pure water and in aqueous PEG solutions have been determined. The effects of temperature and concentration of PEG on the infinite dilution apparent molar volume and the infinite dilution apparent molar isentropic compressibility of monomer and micellar state of both investigsated surfactants in this work have been studied.
