title: The self-assembly structure and the CO2-philicity of a hybrid surfactant in supercritical CO2: effects of hydrocarbon chain length.
abstract: Hybrid surfactants containing both fluorocarbon (FC) and hydrocarbon (HC) chains, as effective CO2-philic surfactants, could improve the solubility of polar substances in supercritical CO2. Varying the length of the HC of hybrid surfactants is an effective way to improve the CO2-philicity. In this paper, we have investigated the effects of the HC length on the self-assembly process and the CO2-philicity of hybrid surfactants (F7Hn, n = 1, 4, 7 and 10) in water/CO2mixtures using molecular dynamics simulations. It is found that the self-assembly time of F7Hn exhibits a maximum when the length of the HC is equal to that of the FC (F7H7). In this case, the investigation of H-bonds between the water core and CO2phase shows that F7H7 has the strongest CO2-philicity because it has the best ability to separate water and CO2. To explain the origin of the differences in separation ability, the analysis of the structures of the reverse micelles shows that there are two competing mechanisms with a shortening HC. Firstly, the volume of F7Hn is reduced, which thus decreases the separation ability. Moreover, this also leads to the curved conformation of the FC. As a result, the separation ability is enhanced. These two mechanisms are balanced in F7H7, which has the best ability to separate water and CO2. Our simulation results demonstrate that the increased volume and the curved conformation of the hybrid surfactant tail could enhance the CO2-philicity in F7Hn surfactants. It is expected that this work will provide valuable information for the design of CO2-philic surfactants.
authors.affiliation: College of Science, China University of Petroleum, 266580 Qingdao, Shandong, China. zhangjun.upc@gmail.com.
authors.forename: Muhan
authors.initials: M
authors.lastname: Wang
authors.affiliation: College of Science, China University of Petroleum, 266580 Qingdao, Shandong, China. zhangjun.upc@gmail.com.
authors.forename: Timing
authors.initials: T
authors.lastname: Fang
authors.affiliation: College of Science, China University of Petroleum, 266580 Qingdao, Shandong, China. zhangjun.upc@gmail.com.
authors.forename: Pan
authors.initials: P
authors.lastname: Wang
authors.affiliation: College of Science, China University of Petroleum, 266580 Qingdao, Shandong, China. zhangjun.upc@gmail.com.
authors.forename: Xinpeng
authors.initials: X
authors.lastname: Tang
authors.affiliation: School of Petroleum Engineering, China University of Petroleum, 266580 Qingdao, Shandong, China.
authors.forename: Baojiang
authors.initials: B
authors.lastname: Sun
authors.affiliation: College of Science, China University of Petroleum, 266580 Qingdao, Shandong, China. zhangjun.upc@gmail.com and Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum, 266580 Qingdao, Shandong, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: College of Science, China University of Petroleum, 266580 Qingdao, Shandong, China. zhangjun.upc@gmail.com.
authors.forename: Bing
authors.initials: B
authors.lastname: Liu