Influence of Sodium Salts on the Micellization and Interfacial Behavior of Cationic Surfactant Dodecyltrimethylammonium Bromide in Aqueous Solution

Micellar and surface properties of aqueous dodecyltrimethylammonium bromide (DTAB) solutions have been studied in the absence and presence of several sodium salts including NaCl, NaH2PO4, Na2HPO4, Na2CO3, Na2SO4, Na3PO4, and Na(3)Cit. The values of critical micelle concentration (cmc), degree of anionic binding (beta), surface tension at the cmc (gamma(cmc)), adsorption efficiency (pC(20)), effectiveness of surface tension reduction (gamma(cmc)), maximum surface excess concentration (G(max)), minimum surface area per molecule (A(min)) at interface of air-liquid, standard Gibbs free energy of micellization (Delta(mic)G degrees), and adsorption at air/water interfaces (Delta G(ad)degrees) were evaluated from the conductivity and surface tension measurements at 298.15 K. The results show that all salts effectively reduce the cmc values of the cationic surfactant DTAB. The ability of the anions to promote the micellization of DTAB decreases in the order of Cit(3-) > PO43- > SO42- > CO32- > HPO42- > Cl- > H2PO4-. The effect of anions of the added salts on the degree of anionic binding of DTAB in aqueous solutions was also studied, and it was found that for each electrolyte type z(+):z(-), the order of beta values is approximately reverse to that of cmc. The obtained results were discussed on the basis of the interaction between the anions of added sodium salts and surfactant DTAB.