Abstract
Surfactant mixtures are used in many different industrial formulations. In this study, the mixed micelle formation behavior of 2 different cationic surfactants, namely dodecyltrimethylammonium bromide (DTAB) and benzyldimethylhexadecylammonium chloride (BDHAC), in the absence and presence of urea at various temperatures (298.15-318.15K) was studied using the conductometric method. The attractive interaction between DTAB and BDHAC was estimated from the values of critical micelle concentration (CMC) and the CMC for ideal mixing (CMCid). Urea increases the CMC value as a result of the enrichment in the surface charge of the micelles/mixed micelles. The values of micellar mole fraction (X-1(Rub) [Rubingh], X-1(M) [Motomura], X-1(Rod) [Rodenas]) and ideal micellar (X-1(id)) of surfactant BDHAC were obtained by different models and are shown to exhibit the high contribution or effective involvement of BDHAC in mixed micelles and increase with increasing BDHAC mole fraction ((1)). Activity coefficients (f(1) and f(2)) were also evaluated from the relevant formula given in the literature. The negative values of the interaction parameters () show the attractive interaction among the studied components. Excess Gibbs free energy (G(ex)) of micellization revealed that the stability of mixed micelles is higher in aqueous solution than in urea solution. The thermodynamic parameters, namely the Gibbs free energy change, enthalpy change, and entropy change (G(m)(o), H-m(o), and S-m(o), respectively), were also calculated from the conventional standard equations.