Micellization properties of mixed cationic gemini and cationic monomeric surfactants in aqueous-ethylene glycol mixture

The surface properties and mixed micellization behavior of binary combinations of cationic gemini (C16-4-C16, 2Br−) tetramethylene-1,4-bis(cetyldimethylammonium bromide) with cationic monomeric surfactants viz. cetyltriphenylphosphonium bromide (CTPB), tetradecyltriphenylphosphonium bromide (TTPB), cetyltributylphosphonium bromide (CTBuPB), cetyldiethylethanolammonium bromide (CDEEAB) and tetradecyldiethylethanolammonium bromide (TDEEAB) have been investigated by surface tension and conductivity measurements in (10%, v/v) ethylene glycol mixture at 300 K. The critical micelle concentration (cmc), surface properties, Γmax (maximum surface excess), Amin (minimum surface area per molecule) and πcmc (surface pressure at the cmc) have been determined. The deviation from the ideal of the mixed micelles has been discussed on the basis of Clint theory. The results of the mixed systems were analyzed in the light of the regular solution theory (Rubingh) and Rosen's theory to evaluate the composition of the mixed micelle, the activity coefficient, the interfacial mole fraction of the surfactant at the mixed adsorbed film and the corresponding interaction parameters (β and βσ). The negative values of interaction parameters (β and βσ) for mixed micelle formation indicate the attractive interaction for all the system. The standard Gibbs free energies of adsorption (ΔG°ads), standard Gibbs free energies of micellization (ΔG°m), the excess free energies of micellization (ΔGex) and minimum free energy of the surface (ΔG(s)min) of gemini with cationic monomeric surfactants were also evaluated. The ΔG°ads, ΔG°m and ΔGex values are negative indicating the spontaneity and stability of the mixed micelle.

Experimental cmc values are very close to those calculated the cmc ideal behavior. The slight negative deviation from ideality indicates nonideality as well as a certain attractive interaction between the surfactants forming the mixed micelles.Figure optionsDownload as PowerPoint slideHighlights
► The surface properties and mixed micelization of cationic gemini and cationic monomeric surfactants are presented.
► The results show that experimental cmc values of all the binary mixtures are less than the ideal cmc.
► The interaction parameters determined from the Rubingh and Rosen equations, are negative indicating in general attractive interaction among surfactant, in both mixed micelle and monolayer formation that in few cases indicates a real synergism.