Experimental and theoretical investigation of micellization behavior of sodium dodecyl sulfate with cetyltrimethylammonium bromide in aqueous/urea solution at various temperatures

Mixed micelle formation behavior of cationic surfactant-cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS) in aqueous as well as in urea medium from 303.15 K to 323.15 K at 5 K interval was carried out by conductometric method. The differences between the experimental values of critical micelle concentrations (cmc) and ideal critical micelle concentrations (cmc(id)) illustrate the interaction between the amphiphiles studied. The values of micellar mole fraction (X-1(Rub) (Rubingh), X-1(M) (Motomura), X-1(Rod) (Rodenas) and X-1(id) (ideal) of surfactant CTAB determined by different proposed models and outcome indicate high involvement of CTAB in SDS-CTAB mixed micellization, which enhance by means of the augment of mole fraction of CTAB. The negative value of interaction parameter (beta) showed an attractive interaction involving CTAB and SDS. Activity coefficients were less than unity in all case, which also reveals the presence of interaction between CTAB & SDS. The negative Delta G(m)(0) values imply the spontaneous mixed micellization phenomenon. The attained values of Delta H-m(0) were positive at inferior temperature, while negative at superior temperature. The negative Delta H-m(0) values in urea (NH2CONH2) medium illustrate exothermic micellization process. The magnitudes of Delta S-m(0) were positive in almost all cases. The excess free energy of mixed micelle formation (Delta G(ex)) was found to be negative, which indicates the stability of mixed micelle as compared to the individual's components micelles.