Tetradecyltrimethylammonium bromide plus dodecyltrimethylammonium bromide mixed micelles in aqueous glycol oligomers

The conductances of tetradecyltrimethylammonium bromide (TTAB)+dodecyltrime thylammonium bromide (DTAB) mixtures over the entire mole fraction range of TTAB (alpha(TTAB)) were measured in pure water as well as in the presence of various aqueous ethylene glycol oligomers containing 5 and 10 wt% of eac h additive in their respective binary mixtures at 30 degrees C. From the co nductivity data, the critical micellar concentrations (cmc) and degrees of micelle ionization Od) for TTAB +DTAB mixtures were computed. From the slop es of the conductivity curves, the equivalent conductivities of the monomer ic (Lambda m), monomeric in the presence of additive (Lambda(m,a)) and the micelle (Lambda(mic)) state were calculated, the results are discussed with respect to the glycol-additive effects in the whole mole fraction range of the binary mixture. The micellar parameters of both surfactants and of the ir mixtures show a significant dependence on the amount in comparison to th e number of repeating units of glycol oligomers. These results have been ex plained on the basis of the medium effects of aqueous additive, which are d rastically influenced by the increase in the amount of additive rather than by the increase in the number of repeating units. The non-ideality in TTAB +DTAB mixtures was evaluated by using the regular solution theory and Moto mura's formulation based on the excess thermodynamic quantities. It has bee n found that the regular solution interaction parameter (beta) and micellar mole fraction ((x) over bar(2)(m)) remain almost unaffected even in the pr esence of up to 10 wt% of each additive and molecular weight 4000. These re sults suggest that there are no significant interactions between the glycol oligomers and the micelles of single and mixed surfactants.