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 R u b (Rubingh), X 1 M (Motomura), X 1 R o d (Rodenas) and X 1 i d (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 ( β ) 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 Δ G m 0 values imply the spontaneous mixed micellization phenomenon. The attained values of Δ H m 0 were positive at inferior temperature, while negative at superior temperature. The negative Δ H m 0 values in urea (NH 2 CONH 2 ) medium illustrate exothermic micellization process. The magnitudes of Δ S m 0 were positive in almost all cases. The excess free energy of mixed micelle formation (ΔG ex ) was found to be negative, which indicates the stability of mixed micelle as compared to the individual’s components micelles.