Abstract:

The mixed adsorption of a cationic gemini surfactant, ethanediyl-1, 2-bis(dodecyldimethylammonium bromide) 12-2-12), and a nonionic surfactant, polyoxyethylene mono-dodecyl ether (C₁₂E_n, where n = 4, 10, 23) at the air/water interface was studied using surface tension measurements. The dilational viscoelastic properties of the films that formed at the air/water interface were examined using an interfacial rheology technique that was described using the Lucassen-van den Tempel (LVT) model. The values of the limit elasticity were fitted accordingly. Foams were generated by the mixed surfactant aqueous solutions and the stability of foams determined using the half-life. C₁₂E_n exhibited attractive interactions towards 12-2-12 within the adsorption films. The average minimum area (Amin) of the adsorbed molecules decreased in the order: 12-2-12/C₁₂E₂₃ > 12-2-12/C₁₂E₁₀ > 12-2-12/C₁₂E₄, while the limit elasticity decreased in the reverse order: ε_{0, fit}(12-2-12/C₁₂E₄) > ε_{0, fit}(12-2-12/C₁₂E₁₀) > ε_{0, fit}(12-2-12/C₁₂E₂₃) at a comparable concentration of the surfactant in the bulk. Compared with the film adsorbed by 12-2-12 alone, only 12-2-12/C₁₂E₄ form had denser structure. Thus, by adding the nonionic component C₁₂E₄, which contained a small hydrophilic head group, the interfacial elasticity of the 12-2-12 film increased significantly and the stability of the corresponding foams was effectively enhanced.

Key words: Mixed adsorption, Cationic gemini surfactant, Nonionic conventional surfactant, Interfacial elasticity, Foam stability