Thermodynamics of aqueous mixtures of 2-(2-Hexyloxyethoxy)ethanol at 5°C

The densities and the ultrasonic speeds of the aqueous solutions of 2-(2-hexyloxyethoxy)ethanol (C₆E₂) were measured over the entire range of mole fractions at 5°C. Excess molar volumes V ^E were readily calculated from the densities. The densities, in combination with the ultrasonic speeds, furnish estimates of the molar (and excess molar) isentropic compressibilities K _S and the deviations u ^D of the ultrasonic speeds from the values calculated for ideal mixtures. Radical changes in the mole fraction derivatives of the excess molar properties of the (C₆E₂ + water) system, in the vicinity of an amphiphile mole fraction of 0.003, indicate that C₆E₂ like C₆E₃ is capable of micelle formation. Our data have been compared with those reported earlier for (C₄E₂ +, C₂E₂ +, and C₆E₃ + water). We have employed both mass action and pseudophase approaches to data analysis, together with the four-segment model approach.