Hydrophobic hydration of cationic mixed micelles by alkoxyethanols in aqueous media

The conductances of hexadecylpyridinium chloride (HPyCl) + tetradecyltrimet hylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyCl (alpha (HPyCl)) were measured in aqueous binary mixtures of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol m onobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoe thyl ether, and diethylene glycol monobutyl ether containing 10 to 30 wt% a dditive in their respective binary mixtures at 30 degreesC. Each conductivi ty curve showed a single break over the whole mole fraction range of HPyCl + TTAB mixtures. From the break in the conductivity curve, various micellar parameters were calculated and the results were discussed on the basis of alkoxyethanol's hydrophobic hydration of the mixed micelle. The micellar pa rameters of HPyCl, TTAB, and of their mixtures showed a strong dependence b oth on the amount and on the number of repeating units of ethylene and diet hylene glycol derivatives. The hydrophobic hydration was considerably highe r in the case of diethylene glycol derivatives owing to the presence of an extra ether oxygen. An evaluation of the non-ideality in the HPyCl + TTAB m ixtures in the presence of additives revealed that alkoxyethanols reduce th e unlike surfactant monomer interactions in order to form the mixed micelle s in comparison to those in pure water. It has also been observed that such interactions systematically decrease with an increase in the number of rep eating units from monomethyl ether to monobutyl ether, both in the case of ethylene and diethylene glycol derivatives.