Thermodynamic and aggregation properties of sodium dodecyl sulfate in aqueous binary mixtures of isomeric butanediols

The effect of aqueous binary mixtures of isomeric butanediols on the micell ization of sodium dodecyl sulfate has been investigated. Conductivity and f luorescence techniques were employed to determine the critical micellar con centration, the degree of dissociation of the counterions and the aggregati on numbers of the surfactants in these binary blends. Differential conducti vity plots were employed to distinguish between the cooperative and the ste pwise aggregation process of the surfactant in each solvent system. The mas s-action model was employed to calculate the hydrophobic and the electrosta tic contributions to the Gibbs energy of micellization as well as the monom er and the counterion concentrations in the postmicellar region. The thermo dynamic parameters calculated for each system indicate that the micellizati on process occurs more readily in the presence of cosolvent owing to the fo rmation of mixed micelles.