Effects of glycol additives on the mixed micelle formation by hexadecyltrimethylammonium bromide plus dodecylpyridinium chloride mixtures

The conductances of hexadecyltrimethylammonium bromide (HTAB) + dodecylpyridinium chloride (DDPCl) mixtures over the entire mole fraction range of HTAB (alpha (HTAB)) were measured in aqueous binary mixtures of ethylene glycol (EG), diethylene glycol (DEG), propylene glycol (PG), butylene glycol (BG), and ethylene glycol monobutyl ether (EGMBE) containing 10 and 20 wt% of each additive in their respective binary mixtures at 30 degreesC. Each conductivity curve showed a single break over the whole mole fraction range of HTAB+DDPCl mixtures except in the presence of BG and EGMBE, where no break was observed for HTAB and even beyond HTAB rich region of the mixtures especially in the presence of 20 wt% BG. It was observed that BG and EGMBE have stronger influence over the variation in the micellar parameters in comparison to that of other glycol additives. The results suggest that HTAB+DDPCl mixtures undergo strong structural changes in DDPC1 rich region in comparison to that of HTAB due to the strong HTAB-additive interactions, whereas such interactions are comparatively very weak in the case of DDPCl. The mixing behavior of HTAB+DDPCl mixtures is quite non-ideal especially in the DDPCl rich region and demonstrates the strong repulsive interactions due to the incompatibility between the unlike bulky polar head groups in this region. (C) 2000 Elsevier Science B.V. All rights reserved.