Mixed micelles of cationic surfactants in aqueous polyethylene glycol 1000

The conductances of tetradecyltrimethylammonium bromide (TTAB) + dodecyltrimethylammonium bromide (DTAB) mixtures over the entire mole fraction range of TTAB (alpha(TTAB)) were measured in aqueous polyethylene glycol 1000 (PEG) containing 1, 2, 5 and 10 wt% of PEG at 30 degrees C. From the conductivity data, various micellar parameters were computed. The results have been explained on the basis of the medium effects as well as the adsorption of additive molecules at micelle-solution interface. The non-ideality in TTAB+DTAB mixtures was evaluated by using the regular solution theory and Motomura's formulation based on the excess thermodynamic quantities. It has been found that the regular solution interaction parameter (beta) and micellar mole fraction (<(x(2)(m))over bar>) remain almost unaffected even in the presence of up to 10 wt% of PEG. These results suggest that the additive remains only in the aqueous phase and perhaps only changing the environment surrounding the micelles by adsorbing at the micelle-solution interface.