Micellar, interfacial and fluorescence investigation on binary mixtures of dodecyl cationic surfactants in aqueous media

The critical micelle concentration (cmc) of binary mixtures of C12-triphenyl phosphonium, pyridinium and trimethyl ammonium bromides were determined employing conductometry, surface tensiometry and fluorescence techniques. Binary mixtures of C12 phosphonium bromide with C12 trimethyl ammonium and pyridinium bromide surfactants exhibited second breaks due to the structural micellar transition, and are supported by conductometric and flurometric methods. The values of surface excess, minimum area of the C12 surfactants at the cmc and Gibbs energy of adsorption were evaluated. The ideality/non-ideality of the mixing was analysed using regular solution theory (RST) to obtain the composition of the mixed micelle and the interaction parameter (βm) to evaluate the strength of interactions of surfactants in the mixed micelles. The tensiometric measurements were also analysed to obtain the interaction parameter (βσ) for the mixed monolayer at the air/water interface. Activity coefficients and the excess free energy of mixing were also determined.