Thermodynamics and Aggregation Number of Surfactants in Water-Acetonitrile Mixtures

Abstract

Cationic surfactants of alkyl (dodecyl, tetradecyl and cetyl) trimethyl ammonium bromide (C₁₂TAB, C₁₄TAB and C₁₆TAB) respectively can be used to study micellization phenomenon in water-acetonitrile mixtures. Their critical micelle concentrations are measured by using different techniques such as conductivity, UV spectra and density at different mole fractions of acetonitrile and temperatures. Effects of adding NaBr to C₁₂TAB and C₁₄TAB solutions are discussed from conductance technique. Thermodynamics of micellization are studied by applying equilibrium model at different X_AN and temperatures. Gibbs energies of transfer per methylene group (dDG/d n_c) are calculated at 298 K but at different X_AN. The differences in partial molar volume (DV_sur.) for those solutions below and above (critical micelle concentration) formed are estimated via density measurements and the related aggregation numbers can be calculated from Huisman’s treatment and compared with DV_sur values. Finally, the Krafft phenomena for given solutions are derived and discussed.