Effect of alcohols on the cmc and micelle ionization degree of alkanediyl-α,ω-bis,(dimethyldodecylammonium bromide) surfactants

The critical micelle concentration (cmc) of three dimeric surfactants of the alkanediyl-alpha,omega-bis(dimethyldodecylammonium bromide) type, one trimeric surfactant and two conventional monomeric surfactants has been measured in the presence of increasing amounts of linear I-alcohols (methanol to hexanol), using the electrical conductivity method. The results show little difference in the variations of cmc(A)/cmc(W) (cmc(A) and cmc(W) = cmc values in a water/alcohol mixture and in water) for the monomeric, dimeric and trimeric surfactant with the alcohol concentration for alcohols that are very soluble in water (methanol and ethanol) or hardly soluble in water (pentanol and hexanol). Significant differences are observed only for alcohols that are partitioned between water and micelles (mainly propanol and butanol). Large differences in the solubility of butanol in micellar solutions of the three dimeric surfactants observed at high surfactant concentration appear to be associated to differences in micelle shape. The ionization of dimeric surfactant micelles in ethanol/water mixtures increases nearly linearly with the ethanol content.