Highly stable foams generated in mixed systems of ethanediyl-1,2-bis(dodecyldimethylammonium bromide) and alcohols

Abstract

Stable foams were generated using a cationic gemini surfactant, ethanediyl-1,2-bis(dodecyldimethylammonium bromide) (12-2-12) together with a linear alcohol, hexanol (C₆OH) or heptanol (C₇OH), in aqueous solution. The foam stability was determined using the half-life of foam height falling (t_1/2) as the index. The results showed that C₇OH was more efficient than C₆OH together with 12-2-12 to stabilize the foams. To generate the most stable foams, the optimum addition for both C₆OH and C₇OH was determined. The adsorption of the mixtures at the air/water interface was studied using surface tension measurements. The intermolecular interactions and the composition of the mixed monolayer were estimated by Rubingh–Rosen theory and the surface excess was derived from the Gibbs equation. The total surface excess that included both 12-2-12 and alcohols, was shown to significantly increase following the addition of alcohols suggesting the active molecules were more densely packed at the interface. The interfacial dilational rheology of the films was examined using the oscillating drop technique. The results showed that a highly stable foam always corresponded to a highly elastic adsorption film. The present study suggests a new formula for the generation of highly stable foams using a gemini surfactant with a short spacer together with a linear alcohol.