Chen An, Chen Jingsi, Wang Duo, Xu Jianhong, Zeng Hongbo
The State Key Lab of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China; Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada.
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada.
J Colloid Interface Sci. 2020 Jul 1;571:134-141. doi: 10.1016/j.jcis.2020.03.045. Epub 2020 Mar 12.
Recently, switchable or stimuli-responsive emulsions have attracted much research interest in many industrial fields. In this work, a novel CO/N-responsive surfactant was designed and developed to facilitate the formation of switchable oil-in-water (O/W) emulsions with fast switching characteristics between a stable emulsion and separate phases upon alternatively bubbling CO and N.
The novel CO/N-responsive surfactant was facilely prepared by mixing an anionic fatty acid (oleic acid) and a cationic amine (1,3-Bis (aminopropyl) tetramethyldisiloxane) at a 1:1 molecular ratio, which was assembled based on electrostatic interactions. The structure and properties of the novel CO/N-responsive switchable surfactant were investigated by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (H NMR) spectroscopy, and interfacial tensions.
The developed surfactant shows an excellent interfacial activity at the oil/water interface, which can significantly reduce the dosage of the switchable surfactant compared with previous CO/N-responsive surfactants. The dynamic interfacial tension of n-decane and aqueous phase decreased from 45 mN m to 5 mN m within 100 s with the addition of 0.2 mM surfactant. In this work, a low concentration of the novel switchable surfactant (e.g., 20.0 mM) can realize reversible emulsification and demulsification in an emulsion system as compared with the high dosage (e.g., ~150 mM) in previous reports, which will bring huge economic benefits in industrial applications in the future. Moreover, this work expands the family of ion-pair surfactants to small amino-functionalized molecules beyond Jeffamine D-230, which promotes the development of simple and switchable ion-pair surfactant. It is found that the O/W emulsions stabilized by the switchable surfactant show excellent stability, which can be stored for over 60 days at room temperature without any obvious change. Interestingly, the stable O/W emulsion is completely demulsified upon bubbling CO for 30 s and can be easily re-emulsified to the initial state after purging N at 60 °C within 10 min, which demonstrates a rapid and highly efficient switching behavior. The reversible emulsification and demulsification process is ascribed to the reversible assembly and disassembly of the switchable surfactant, which is induced by the removal and purge of CO.
近年来，可切换或刺激响应型乳液在许多工业领域引起了广泛的研究兴趣。在本研究中，设计并开发了一种新型的CO/N响应型表面活性剂，以促进形成具有快速切换特性的可切换水包油（O/W）乳液，即在交替通入CO和N时，能在稳定乳液和分离相之间快速切换。
通过将阴离子脂肪酸（油酸）和阳离子胺（1,3-双（氨丙基）四甲基二硅氧烷）按1:1的分子比例混合，简便地制备了这种新型CO/N响应型表面活性剂，其基于静电相互作用进行组装。通过傅里叶变换红外光谱（FTIR）、质子核磁共振（H NMR）光谱和界面张力研究了新型CO/N响应型可切换表面活性剂的结构和性能。
所开发的表面活性剂在油/水界面表现出优异的界面活性，与先前的CO/N响应型表面活性剂相比，可显著降低可切换表面活性剂的用量。加入0.2 mM表面活性剂后，正癸烷与水相之间的动态界面张力在100 s内从45 mN/m降至5 mN/m。在本研究中，与先前报道中的高用量（例如~150 mM）相比，低浓度的新型可切换表面活性剂（例如20.0 mM）就能在乳液体系中实现可逆乳化和破乳，这将在未来的工业应用中带来巨大的经济效益。此外，本研究将离子对表面活性剂家族扩展到了除Jeffamine D-230之外的小氨基官能化分子，推动了简单且可切换离子对表面活性剂的发展。研究发现，由可切换表面活性剂稳定的O/W乳液表现出优异的稳定性，在室温下可储存60多天而无明显变化。有趣的是，稳定的O/W乳液在通入CO 30 s后完全破乳，在60℃下吹扫N 10 min后可轻松重新乳化至初始状态，这展示了快速且高效的切换行为。可逆乳化和破乳过程归因于可切换表面活性剂的可逆组装和解组装，这是由CO的去除和吹扫诱导的。
