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

The nature and thermodynamics of interactions of the cationic surfactant do decyltrimethylammonium bromide (DTA) with the nonionic surfactant Triton X- 100 (TX100) in mixtures are studied using the potentiometric method. We inv estigate the influence of temperature, the addition of KBr, and the concent rations of DTA and TX100 on the complex formation between free DTA cations and TX100 nonionic micelles in solution. Binding isotherms, distribution co efficients K-x, and stoichiometric equilibrium constants K-1 are determined from the experimental data. The standard free energy change (Delta G(1)deg rees), the standard enthalpy change (Delta H(1)degrees) and the standard en tropy change (Delta S(1)degrees) are calculated for transferring the free D TA cation from the aqueous bulk phase to the TX100 nonionic micelle phase. Our results support the assumption that hydrophobic interactions are the mo st important in this binding process.