Interfacial dilational viscoelasticity and foam stability in quaternary ammonium gemini surfactant systems: influence of intermolecular hydrogen bonding

This paper reports the adsorption and interfacial viscoelasticity of gemini surfactants with a hydroxyl-substituted spacer, 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide), 2-hydroxyl-butanediyl-α,ω-bis(dimethyldodecylammonium bromide), and 2,3-hydroxyl-butanediyl-α,ω-bis(dimethyldodecylammonium bromide), referred to as 12-3(OH)-12, 12-4(OH)-12, and 12-4(OH)₂-12, respectively, at the air/water interface using dropping shape and interface dilational rheology measurements. For comparison, the unsubstituted surfactants were also examined at identical conditions. The results showed that substituted surfactants produced a remarkably higher interfacial elasticity than the corresponding unsubstituted ones. This was attributed to the effect of the intermolecular hydrogen bonding occurring between the hydroxyl-substituted spacers of adsorbed molecules, which resulted in tighter packing of the molecules in the monolayer. Besides, we measured foam stability. The foam produced by the substituted geminis was found to have higher stability than that by the unsubstituted geminis. It was suggested that the foam stability may be related to the limit elasticity of interfacial film at the level of identical surface excesses.