Yi Lu1, Dejun Sun2, John Ralston3, Qingxia Liu4, Zhenghe Xu5. 1. Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada. Electronic address: lu13@ualberta.ca. 2. Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan, Shandong 250100, PR China. Electronic address: djsun@sdu.edu.cn. 3. Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: John.Ralston@unisa.edu.au. 4. Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada. Electronic address: qingxia2@ualberta.ca. 5. Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada; Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, PR China. Electronic address: zhenghe@ualberta.ca.
Abstract
HYPOTHESIS: One of the major challenges in applying CO2-responsive surfactants concerns their tunable switchability and robustness under operating conditions. We hypothesize that combining monoethanolamine (MEA) with long-chain fatty acids (LCFAs) of variable chain lengths through electrostatic attraction could develop a series of CO2-responsive surfactants with tunable switching pH. EXPERIMENTS: The tunability of switching pH for this group of surfactants was demonstrated by in situ probing of the CO2-responsive characteristics at the oil/water interface using dynamic interfacial tension (IFT) measurements. Two protocols were applied to distinguish interfacial response and solution response. The key importance of interfacial response was demonstrated by two essential applications of CO2-responsive surfactants: demulsification of stable emulsions, and alternation of the interfacial properties of ultra-heavy crude oil-water interfaces. FINDINGS: The switching pH of the CO2-responsive surfactants was controlled by the hydrocarbon chain length of LCFAs. More importantly, their switching behaviour was found to be different at the interface and in the bulk solution, which is attributed to the enhanced molecular interactions at the interface. Since most applications require surfactants to be switched at the interface, it is thereby most appropriate to determine the switching pH through their interfacial responses.
HYPOTHESIS: One of the major challenges in applying CO2-responsive surfactants concerns their tunable switchability and robustness under operating conditions. We hypothesize that combining monoethanolamine (MEA) with long-chain fatty acids (LCFAs) of variable chain lengths through electrostatic attraction could develop a series of CO2-responsive surfactants with tunable switching pH. EXPERIMENTS: The tunability of switching pH for this group of surfactants was demonstrated by in situ probing of the CO2-responsive characteristics at the oil/water interface using dynamic interfacial tension (IFT) measurements. Two protocols were applied to distinguish interfacial response and solution response. The key importance of interfacial response was demonstrated by two essential applications of CO2-responsive surfactants: demulsification of stable emulsions, and alternation of the interfacial properties of ultra-heavy crude oil-water interfaces. FINDINGS: The switching pH of the CO2-responsive surfactants was controlled by the hydrocarbon chain length of LCFAs. More importantly, their switching behaviour was found to be different at the interface and in the bulk solution, which is attributed to the enhanced molecular interactions at the interface. Since most applications require surfactants to be switched at the interface, it is thereby most appropriate to determine the switching pH through their interfacial responses.
Authors: Martin Reifarth; Marek Bekir; Alain M Bapolisi; Evgenii Titov; Fabian Nußhardt; Julius Nowaczyk; Dmitry Grigoriev; Anjali Sharma; Peter Saalfrank; Svetlana Santer; Matthias Hartlieb; Alexander Böker Journal: Angew Chem Int Ed Engl Date: 2022-03-23 Impact factor: 16.823