Micellar transitions of mixtures of cationic surfactants - Influence of alkoxyethanols on the micellar transitions of hexadecylpyridinium bromide andtetradecyltrimethylammonium bromide surfactant mixtures

The conductivities of binary surfactant mixtures of hexadecylpyridinium bro mide (HPyBr) and tetradecyltrimethylammonium bromide (TTAB) over the entire mole fraction range of HPyBr (alpha (HPyBr)) were measured in the presence of diethylene glycol monomethyl ether (DEGMME), diethylene glycol monoethy l ether (DEGMEE) and diethylene glycol monobutyl ether (DEGMBE) containing 10 and 30 % w/w of each additive in their respective binary mixtures at 30 degreesC. Each conductivity curve shows two breaks corresponding to two c.m .c. values, i.e. C-1 and C-2, in 10% w/w DEGMME and DEGMEE over the whole m ole fraction range of HPyBr + TTAB mixtures, except in the presence of pure HPyBr and TTAB, as well as in aqueous 30 % w/w alkoxyethanols, where a sin gle break was observed. From the conductivity data, various micellar parame ters in the presence of alkoxyethanols were computed. A variation in the mi cellar parameters in the presence of alkoxyethanols showed that the inducti on of additive primarily adsorbs at the micelle-solution interface existing at C-1 and C-2, and secondarily influences the medium properties, owing to which the micellar transitions occurring at C-2 are suppressed. The mixing behavior of HPyBr + TTAB is close to non-ideal and quite similar in pure w ater and in the presence of Various alkoxyethanols. It has been concluded t hat the alkoxyethanol molecules only adsorb at the micelle-solution interfa ce and do not penetrate deep into the mixed micelles.