Effect of the Surfactant C12mimBr on the Aggregation Behavior of Gemini12-2-12 at an Air/Water Interface, Investigated Using an Interfacial Dilational Rheology Method

The dynamic interfacial tension, dilational rheological properties, and interfacial relaxation processes of quaternary ammonium Gemini surfactant C-12-(CH2)(2)-C-12 center dot 2Br (Gemini12-2-12) solutions and Gemini12-2-12/ionic liquid surfactant C(12)mimBr mixed systems at an air/water interface were investigated using an interfacial dilational rheology method at low frequencies (0.02-0.50 Hz). The effect of the C(12)mimBr on the interfacial properties of the Gemini12-2-12/C(12)mimBr mixed systems, and the mechanism responsible for the influence of C(12)mimBr on the aggregation behavior of the Gemini12-2-12 at the air/water interface, are discussed here. The experimental results showed that with increasing the amount of C(12)mimBr, the time required to achieve interfacial adsorption equilibrium for the mixed systems was reduced, the dilational moduli and phase angle in the mixed systems decreased, and the interfacial adsorption films were inclined to become elastic. Simultaneously, the relaxation processes at the interface or near the interface changed significantly, the slow relaxation process disappeared, and a fast relaxation process dominated the properties of the interfacial films. Moreover, the contribution of the fast relaxation process increased with increasing the concentration of C(12)mimBr. The abovementioned changes in the interfacial properties were mainly attributed to the participation of the C(12)mimBr in the formation of the interface, and the competitive adsorption of the two surfactants at the air/water interface. At lower concentrations of C(12)mimBr, the C(12)mimBr molecules filled the vacancies between the Gemini12-2-12 molecules when the Gemini12-2-12 molecules were loosely arranged at the interface, and mixed-adsorption films formed from C(12)mimBr and Gemini12-2-12 spread on the air/water interface. With increasing the concentration of C(12)mimBr, the alkyl chains of the Gemini12-2-12 molecules that were wrapped around each other at the air/water interface untangled, and the Gemini12-2-12 molecules underwent desorption from the interface. At the same time, C(12)mimBr molecules replaced Gemini12-2-12 molecules, because of their low steric hindrance and strong hydrophobic effects; ultimately, C(12)mimBr molecules almost entirely occupied the air/water interface.

采用低频（0.02 - 0.50 Hz）界面扩张流变方法研究了季铵盐Gemini表面活性剂C - 12 - (CH₂)₂ - C - 12·2Br（Gemini12 - 2 - 12）溶液以及Gemini12 - 2 - 12/离子液体表面活性剂C₁₂mimBr混合体系在气/水界面的动态界面张力、扩张流变性质和界面松弛过程。本文讨论了C₁₂mimBr对Gemini12 - 2 - 12/C₁₂mimBr混合体系界面性质的影响，以及C₁₂mimBr影响Gemini12 - 2 - 12在气/水界面聚集行为的作用机制。实验结果表明，随着C₁₂mimBr含量的增加，混合体系达到界面吸附平衡所需的时间缩短，混合体系的扩张模量和相位角减小，界面吸附膜趋于弹性化。同时，界面处或界面附近的松弛过程发生显著变化，慢松弛过程消失，快松弛过程主导界面膜的性质。此外，快松弛过程的贡献随着C₁₂mimBr浓度的增加而增大。上述界面性质的变化主要归因于C₁₂mimBr参与界面的形成以及两种表面活性剂在气/水界面的竞争吸附。在较低的C₁₂mimBr浓度下，当Gemini12 - 2 - 12分子在界面松散排列时，C₁₂mimBr分子填充在Gemini12 - 2 - 12分子之间的空位，由C₁₂mimBr和Gemini12 - 2 - 12形成的混合吸附膜在气/水界面铺展。随着C₁₂mimBr浓度的增加，在气/水界面相互缠绕的Gemini12 - 2 - 12分子的烷基链解开，Gemini12 - 2 - 12分子从界面解吸。同时，由于C₁₂mimBr分子的空间位阻小且疏水作用强，它取代了Gemini12 - 2 - 12分子；最终，C₁₂mimBr分子几乎完全占据气/水界面。