The Effects of Polyoxyethylene Chain Length Distribution on the Interface Properties of Polyoxyethylenated N-Dodecyl Alcohols

Abstract

Assuming ideal mixing behavior, the effects of different Gaussian distribution in polyoxyethylene (POE) chain length of surfactants prepared from mono-polyoxyethylene glycol n-dodecyl alcohols on the thermodynamic properties of surface adsorption of mixed surfactants and of mixed micelle formation in aqueous solution are discussed in comparison with monodispersed or normally dispersed surfactants. Experimental results indicate that the assumption of ideal mixing for homologous mixtures is valid. The surface adsorption (Γ∞) and the surface pressure (πcmc) of the mixed solution are increased with the increase of distribution coefficient resulting in a close molecular orientation at the interface, while the CMC is decreased slightly. The molecules of the adducts with short РОЕ chain dominate both in mixed adsorbed layers and in micelles. Solubilization of ethylbenzene can be expressed by a linear additive relation. The calculated compositions of mixed micelles are confirmed by the solubilization experiments. Detergency performance of mixed solutions of C12En with distribution in POE chain length is superior to that of monodispersed С12En, but the effect is not noticeable beyond a certain range or distribution.