界面扩张流变法研究C_(12)mimBr对Gemini12-2-12在空气/水界面聚集行为的影响

采用界面扩张流变技术研究了季铵盐偶联表面活性剂C12-(CH2)2-C12·2Br(Gemini12-2-12)及其与离子液体表面活性剂溴化1-十二烷基-3-甲基咪唑(C12mim Br)复配体系的动态界面张力、扩张流变性质和界面弛豫过程等,探讨了C12mim Br对C12mim Br/Gemini12-2-12混合体系界面性质的影响及C12mim Br对Gemini12-2-12界面聚集行为影响的机制.结果表明,随着离子液体表面活性剂的不断引入,体系界面吸附达到平衡所需的时间逐渐缩短,扩张模量和相角明显降低,界面吸附膜由粘弹性膜转变为近似纯弹性膜;同时,界面及其附近的弛豫过程也发生显著变化,慢弛豫过程消失,快弛豫过程占主导地位,且离子液体浓度越高,快弛豫的贡献越大.这些界面性质的变化主要归因于离子液体表面活性剂C12mim Br参与界面形成及两表面活性剂在界面竞争吸附的结果.少量离子液体表面活性剂C12mim Br的加入可以填补疏松的Gemini12-2-12界面上的空位,形成混合界面吸附膜.随着C12mim Br含量的增加,嵌入界面的C12mim Br分子数不断增多,导致界面上相互缠绕的Gemini12-2-12烷基链"解缠",在体相和界面分子扩散交换的过程中"解缠"的Gemini12-2-12分子从界面上解吸回到体相,与此同时,C12mim Br分子相对较小的空间位阻及较强的疏水作用促使其优先扩散至界面进而取代Gemini12-2-12分子,最终界面几乎完全被C12mim Br分子所占据.

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 C₁₂-(CH₂)₂-C₁₂·2Br (Gemini12-2-12) solutions and Gemini12-2-12/ ionic liquid surfactant C₁₂mimBr 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 C₁₂mimBr on the interfacial properties of the Gemini12-2-12/C₁₂mimBr mixed systems, and the mechanism responsible for the influence of C₁₂mimBr 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 C₁₂mimBr, 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 C₁₂mimBr. The abovementioned changes in the interfacial properties were mainly attributed to the participation of the C₁₂mimBr in the formation of the interface, and the competitive adsorption of the two surfactants at the air/water interface. At lower concentrations of C₁₂mimBr, the C₁₂mimBr molecules filled the vacancies between the Gemini12-2-12 molecules when the Gemini12-2-12 molecules were loosely arranged at the interface, and mixedadsorption films formed from C₁₂mimBr and Gemini12-2-12 spread on the air/water interface. With increasing the concentration of C₁₂mimBr, 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, C₁₂mimBr molecules replaced Gemini12-2-12 molecules, because of their low steric hindrance and strong hydrophobic effects; ultimately, C₁₂mimBr molecules almost entirely occupied the air/water interface.