Mixed micelles of hexadecylpyridinium bromide plus tetradecyltrimethylammonium bromide in aqueous glycol oligomers

Conductances of hexadecylpyridinium bromide (HPyBr) + tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyBr (alpha(HPyBr)) were measured in pure water as well as in the presence of various aqueous ethylene glycol oligomers containing 10 and 30 wt% of each additive in their respective binary mixtures at 30 degrees C. Each conductivity curve shows two breaks corresponding to two critical micelle concentrations (cmc; C-1 and C-2 over the whole mole fraction range of HPyBr + TTAB mixtures except in the presence of pure HPyBr and TTAB, where a single break was observed. From the conductivity data, various micellar parameters in the absence and presence of glycol additives were computed. A variation in the micellar parameters in the presence of additive showed that additive introduction mainly influences the medium properties and therefore the micellar properties. However, no significant micelle-glycol interactions were observed even with an increase in the number of repeating units from ethylene glycol to polyethylene glycol 600. The mixing behavior of HPyBr + TTAB is close to nonideal and is identical in pure water and in the presence of various glycols. This has been attributed to the presence of synergistic interactions between unlike monomers at C-1 that are not influenced even by the presence of additives. The appearance of the second cmc is mainly attributed to structural transitions of the mixed micelles at C-1 with a further increase in surfactant concentration.