Potentiometric study of intermolecular interactions in cationic-nonionic mixed surfactant systems

The nature and thermodynamics of interactions of the cationic surfactant dodecyltrimethylammonium bromide (DTA) with the nonionic surfactant Triton X-100 (TX100) in mixtures are studied using the potentiometric method. We investigate the influence of temperature, the addition of KBr, and the concentrations of DTA and TX100 on the complex formation between free DTA cations and TX100 nonionic micelles in solution. Binding isotherms, distribution coefficients K-x, and stoichiometric equilibrium constants K-1 are determined from the experimental data. The standard free energy change (Delta G(1)degrees), the standard enthalpy change (Delta H(1)degrees) and the standard entropy change (Delta S(1)degrees) are calculated for transferring the free DTA cation from the aqueous bulk phase to the TX100 nonionic micelle phase. Our results support the assumption that hydrophobic interactions are the most important in this binding process.