Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University , Jinan, Shandong 250100, People's Republic of China.
Department of Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta T6G 2 V4, Canada.
Langmuir. 2017 Mar 28;33(12):3040-3046. doi: 10.1021/acs.langmuir.6b04546. Epub 2017 Mar 17.
Dynamic covalent surfactants were designed to prepare pH switchable emulsions. A dynamic covalent bond between nonamphiphilic building blocks (polyethylenimine (PEI) and benzaldehyde (B)) was introduced to form the dynamic covalent surfactant PEI-B. The dynamic nature of covalent bond in PEI-B was confirmed by H NMR and fluorescence probe analysis. Stable emulsions were successfully prepared with interfacial active PEI-B at pH 7.8 with various water/paraffin oil ratios under sonication. When lowering the pH to 3.5, a complete phase separation was observed as a result of breaking dynamic covalent bond in the interfacial active PEI-B. After tuning the pH back to 7.8, stable emulsion was obtained again due to the reformation of the dynamic covalent bond and hence interfacial active PEI-B. The emulsification and demulsification were dependent on the formation and breaking of dynamic covalent bond in PEI-B. Such pH-triggered emulsification and demulsification can be switched at least three times. Application of dynamic covalent surfactants will open up a novel route for preparing responsive emulsions.
动态共价表面活性剂被设计用来制备 pH 可切换乳液。在非两亲性构建块（聚乙烯亚胺 (PEI) 和苯甲醛 (B)）之间引入了动态共价键，形成了动态共价表面活性剂 PEI-B。通过 1H NMR 和荧光探针分析证实了 PEI-B 中共价键的动态性质。在超声作用下，PEI-B 在 pH 7.8 时具有界面活性，可成功制备各种水/石蜡油比的稳定乳液。当 pH 降低至 3.5 时，由于界面活性 PEI-B 中的动态共价键断裂，观察到完全的相分离。将 pH 调回 7.8 后，由于动态共价键的重新形成和界面活性 PEI-B 的形成，再次获得了稳定的乳液。乳化和破乳取决于 PEI-B 中动态共价键的形成和断裂。这种 pH 触发的乳化和破乳可以至少切换三次。动态共价表面活性剂的应用将为制备响应性乳液开辟一条新途径。
