Interaction and micellar behavior of aqueous mixtures of surface active ionic liquid and cationic surfactant: experimental and theoretical studies

The interaction between an ionic liquid (1-dodecyl-3-methylimidazolium bromide or IL) and cationic surfactant (dodecyltrimethylammonium bromide (DTAB)) in aqueous solution has been investigated at various mole fractions and temperature 30 ˚C using experimental and theoretical methods. The critical micelle concentration (CMC) of pure components and their binary mixtures, mixed micellar composition at ideal state( and ) and real state( and ), interaction parameter ( ), activity coefficients of components in mixed micelles ( and ), the standard Gibbs energy of micellization ( ) values and the degree of counterion binding(α) have been calculated and discussed. It has been found for the DTAB/IL mixture that depending on the ionic liquid bulk concentration (y1), repulsive or attractive interactions (positive or negative value of ) are produced in mixed micelle formation. The unique role of IL in changing behaviors of aqueous surfactant mixtures is described. In the theoretical section, the molecular interaction energy of the pure IL, pure DTAB, and mixed IL-DTAB have been estimated using density functional theory (DFT) calculations. The value of interaction energy parameter ( ) has also been calculated at mole fraction of 0.5 and a good agreement with the experimental results was observed.