Thermodynamic Study on the Micellar Properties of DBS/Brij 30 Mixed Surfactant Systems

The critical micelle concentrations (CMC) and the counter ion binding constants (B) in a micellar state of the mixed surfactant systems of sodium dodecylbenzenesulfonate (DBS) with polyoxyethylene(4) lauryl ether ( Brij 30) in water were determined as a function of alpha(1) (the overall mole fraction of DBS) by the use of electric conductivity method and surface tensiometer method from 288 K to 308 K. Various thermodynamic parameters (Delta S-m(o), Delta H-m(o), and Delta G(m)(o) ) for the micellization of DBS/Brij 30 mixtures were calculated and analyzed from the temperature dependence of CMC values. The measured values of Delta G(m)(o) are all negative but the values of Delta S-m(o) are positive in the whole measured temperature region. On the other hand, the values of Delta H-m(o) are positive or negative, depending on the measured temperature and alpha(1).