Influence of NaCl/urea on the aggregation behavior of dodecyltrimethylammonium chloride and sodium dodecyl sulfate at varying temperatures and compositions: Experimental and theoretical approach

Aggregation behavior of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium chloride (DTAC) has been studied by conductivity measurement in aqueous/urea/NaCl medium. The deviation of experimentally executed critical micelle concentration (cmc) from their respective ideal values (cmc(id)) signifies the interaction between the studied surfactants. The experiments were performed at different temperatures in order to estimate different thermodynamic parameters. The negative values of Gibbs free energy (Delta G(m)(o)) point out the feasibility of the micellization behavior of the mixed systems as well as validate the feasibility of SDS-DTAC interactions. The micellar mole fraction (X-1) and the activity coefficients (f(1) and f(2)) on the basis of different proposed model (Rubingh, Motomura, & Rodenas) and ideal mole fraction (X-id) were estimated, and obtained results illustrate the high contribution of DTAC in the mixed micellization, which exacerbates with the increase of the mole fraction of the DTAC. The interaction parameter (beta) has also been investigated to get detailed insights of the interactions between the surfactants by concerning theoretical model proposed by Rubingh. The Delta G(ex) values were attained to be negative at all alpha(1) and temperatures, showing that mixed micelles are more stable than micelles of individual surfactants.