Micellization of cationic surfactants in alcohol — water mixed solvent media

Abstract

The effect of addition of methanol and ethanol on the micellization of cationic surfactants dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB) in aqueous medium have been studied by conductance and surface tension measurements at 298.15K. Different physicochemical properties such as Gibb's free energy of micellization (ΔG°m), free energy of surfactant tail transfer (ΔG°trans), maximum surface excess concentration (Гmax), area occupied by surfactant molecule (Amin), surface pressure at the cmc (πcmc), packing parameters (P) and standard free energy interfacial adsorption (ΔG°ads) are calculated in water, 0.10, 0.20, 0.30 and 0.40 volume fractions of methanol–water and in water, 0.10, 0.20, 0.30, 0.40, 0.50 and 0.60 volume fractions of ethanol–water respectively at 298.15K. Addition of alcohol significantly affects the physicochemical properties of both DTAB and CTAB. With increasing concentration of alcohol, cohesive force and dielectric constant decrease that affects the micellization and other physicochemical properties. However, at the higher volume fraction of ethanol–water a slight variation of properties are seen.The micellization of DTAB and CTAB have been assessed in terms of different solvent parameters. The ratio of the solvent surface tension to the limiting surface tension at the cmc has been used as the solvophobic effect. The solvophobic parameter characterized by Gibbs energy of transfer of hydrocarbon from gas into a given solvent can be used to account for the effect of alcohol on the formation and growth of the cationic surfactants aggregate in water.