Evaluation of mixed micellar interactions of C_nBCl and SDBS mixtures using dissociated Margules model and influence of different salts

The conductivity measurement has been used to determine the first and second CMC's (CMC1 and CMC2) of alkyldimethylbenzylammonium chloride (CnBCl; n = 12, 14 and 16) as well as gemini surfactant trimethylene-1,2-bis-(dodecyldimethylammonium bromide) (12-2-12) with sodium dodecylbenzenesulphonate (SDBS) in aqueous solutions using Rubingh's the regular theory approximation as well as the dissociated Margules Model. The use of Margules model allows us to calculate activity coefficients of the constituents and hence provides better values of micellar parameters for asymmetric mixed systems as compared to the regular solution theory. The CMC1 values for CnBCl/SDBS mixtures were seen to be lower than those predicted from their ideal mixtures suggesting synergistic interactions although the synergism increases with chain length (n) of the cationic surfactant. Both CMC1 and CMC2 experience a decrease with rising values of n. The addition of salts including NaCl, KCl, NaBr, Na3PO4, and Na2SO4 in mixtures of C16BCl and SDBS suggests that salt counterions have a considerable impact on CMC1 when either surfactant is in excess. Zeta potential (zeta) measurements provide more evidence in favor of these observations. The thermodynamic features of micellization have also been scrutinized using isothermal titration calorimetry (ITC).