Gemini表面活性剂/C12En混合体系的界面吸附、扩张粘弹与泡沫稳定性

用表面张力法研究了阳离子gemini表面活性剂乙基-1, 2-双(十二烷基二甲基溴化铵)(简写为12-2-12)和非离子表面活性剂十二烷基聚氧乙烯醚(C₁₂E_n,其中n = 4, 10, 23)混合体系在气液界面上的吸附行为;用扩张流变技术研究了吸附膜的扩张粘弹行为,实验数据用Lucassen-van den Tempel (LVT)模型进行拟合并根据模型得到了极限弹性值.最后研究了混合体系的泡沫行为,用泡沫塌陷到初始高度一半所对应的时间(t_1/2)来表征泡沫的稳定性.结果表明,所有的非离子表面活性剂C₁₂E_n均与12-2-12产生了吸引作用.在12-2-12浓度相同的情况下,混合吸附层中吸附分子的最小分子占据面积的顺序为12-2-12/C₁₂E₂₃ > 12-2-12/C₁₂E₁₀ > 12-2-12/C₁₂E₄,而极限弹性的顺序为ε_{0, fit}(12-2-12/C₁₂E₄) > ε_{0, fit}(12-2-12/C₁₂E₁₀) > ε_{0, fit}(12-2-12/C₁₂E₂₃).与单组分12-2-12形成的吸附膜相比,只有12-2-12/C₁₂E₄形成更加紧密的结构.具有较小亲水头基的非离子表面活性剂C₁₂E₄的加入,可增强12-2-12吸附膜的弹性,进而增强了对应体系泡沫的稳定性.

Interfacial Adsorption,Dilational Visco-Elasticity and Foam Stability in a Mixed System of Gemini Surfactant/C12En

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.