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Zhu H, Li Y, Zhou D, Xu Q, Yin J. Molecular dynamics study on microstructure of supercritical CO2 microemulsions containing ionic liquids. Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2020.125272] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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2
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Shim Y. Computer simulation study of fluorocarbon phosphate surfactant based aqueous reverse micelle in supercritical CO 2: roles of surfactant functional groups, ionic strength, and phase changes in CO 2. Phys Chem Chem Phys 2020; 22:3434-3445. [PMID: 31984986 DOI: 10.1039/c9cp06613f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Structural and dynamic properties of an aqueous micelle organized from fluorocarbon phosphate surfactant molecules in supercritical carbon dioxide (CO2) are investigated via molecular dynamics computer simulations. The roles of the functional groups and ionic strength of the surfactants on the formation of reverse micelles in supercritical CO2, and related water dynamics characterized as translational and reorientational dynamics, are systematically demonstrated by employing three different phosphate-based surfactants paired with sodium cations. The strong electrostatic interactions between the phosphate head groups and sodium cations result in formation of an aqueous core inside the surfactant aggregates, where water molecules are bonded together with loss of the tetrahedral hydrogen bonded network found in bulk water. It is found that all the three surfactants with CO2-philic fluorocarbon double tails build up well-stabilized reverse micelles in supercritical CO2, avoiding direct contacts between CO2 and water molecules. Despite this, the surfactant with a carboxylic ester linkage between the phosphate head and fluorocarbon tail group tends to coordinate water molecules toward sustaining the inter-water hydrogen bonds, indicating better efficiency at covering the aqueous core with hydrophobic groups compared to one without a carboxylic ester group. As for water molecules confined in the reverse micelle, their translational and reorientational motions, and fluctuating dynamics of the inter-water hydrogen bonds, significantly slow down compared to bulk water at ambient temperature. The water dynamics become more restricted with an increase in ionic strength of the anionic surfactant; this is attributed to divalent surfactant heads and sodium cations being more tightly bound together with bonding to water compared to monovalent ones. Lastly, the structural and dynamic changes of the reverse micelle caused by a phase change in CO2 are monitored with gradually decreasing temperature and pressure from the supercritical to gaseous state for CO2. The average reverse micelle structure equilibrated in supercritical CO2 is found to remain stable over a time period of 0.2 ms through a depressurization process to gaseous CO2. We note that the diverse pathways of surfactant self-aggregation in gaseous CO2 could be controlled by the preceding solvation procedure in the supercritical regime which governs the final aggregated structures in gaseous CO2.
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Affiliation(s)
- Youngseon Shim
- CAE Group, Autonomous Material Development Laboratory, Samsung Advanced Institute of Technology, Samsung Electronics, Suwon, Gyeonggi 16678, Korea.
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Stabilization of 4FS(EO)2 constructed water-in-carbon dioxide microemulsions (W/C μEs) with nonfluorinated co-surfactants. J Supercrit Fluids 2019. [DOI: 10.1016/j.supflu.2019.03.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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4
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Wang M, Fang T, Zhong H, Li J, Yan Y, Zhang J. Optimal aggregation number of reverse micelles in supercritical carbon dioxide: a theoretical perspective. SOFT MATTER 2019; 15:3323-3329. [PMID: 30924475 DOI: 10.1039/c8sm02299b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The aggregation number is one of the most fundamental and important structural parameters for the micelle or reverse micelle (RM) system. In this work, a simple, reliable method for the determination of the aggregation number of RMs in supercritical CO2 (scCO2) was presented through a molecular dynamics simulation. The process of pulling surfactants out of the RMs one by one was performed to calculate the aggregation number. The free energies of RMs with different numbers of surfactants were calculated through this process. We found an RM with the lowest free energy, which was considered to have the optimal number of surfactants. Therefore, the optimal aggregation number of RMs was acquired. In order to explain the existence of an optimal aggregation number, detailed analyses of surfactant accumulation were conducted by combining molecular dynamics with quantum chemistry methods. The results indicated that in the RMs with the lowest free energy, the head-group and tail-terminal of the surfactants accumulated on an equipotential surface. In this case, the surfactant film could effectively separate water and CO2; thus, the lowest free energy was expected. This method determined the aggregation number of RMs by theoretical calculations that did not depend on experimental measurements. This presented approach facilitates the evaluation of the characteristics of RMs in scCO2 and can be further applied in the RM system of organic solvents or even in the micellar system.
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Affiliation(s)
- Muhan Wang
- School of Materials Science and Engineering, China University of Petroleum, 266580 Qingdao, Shandong, China.
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Wang M, Wang J, Fang T, Yan Y, Wang Z, Zhang J. Shape transition of water-in-CO2 reverse micelles controlled by the surfactant midpiece. Phys Chem Chem Phys 2018; 20:15535-15542. [DOI: 10.1039/c8cp01844h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Designing CO2-philic surfactants for generating wormlike reverse micelles (RMs) is an effective approach to enhance the viscosity of supercritical CO2 (scCO2), however this remains challenging.
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Affiliation(s)
- Muhan Wang
- College of Science, China University of Petroleum
- 266580 Qingdao
- China
| | - Junfeng Wang
- College of Science, China University of Petroleum
- 266580 Qingdao
- China
| | - Timing Fang
- College of Science, China University of Petroleum
- 266580 Qingdao
- China
| | - Youguo Yan
- College of Science, China University of Petroleum
- 266580 Qingdao
- China
| | - Zhiyuan Wang
- School of Petroleum Engineering
- China University of Petroleum
- 266580 Qingdao
- China
| | - Jun Zhang
- College of Science, China University of Petroleum
- 266580 Qingdao
- China
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Wang M, Fang T, Wang P, Yan Y, Zhang J, Liu B, Sun X. Molecular-Scale Design of Hydrocarbon Surfactant Self-Assembly in Supercritical CO 2. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:5291-5297. [PMID: 28485950 DOI: 10.1021/acs.langmuir.7b01176] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Forming wormlike reverse micelles (RMs) by hydrocarbon surfactant self-assembly is an economic and environmental strategy to improve the physicochemical properties of supercritical carbon dioxide (scCO2), but it remains challenging. Introducing cosurfactant in hydrocarbon surfactant self-assembly system is a potential method to generate wormlike RMs. Here, adopting molecular dynamics simulations, we performed hydrocarbon surfactant (TC14) self-assembly with introducing cosurfactants (C8Benz). It is found that adding the C8Benz molecules will induce the spherical RMs to a short rodlike form. In this case, the microstructure of the short rodlike RMs shows a dumbbell-like form that is composed by three parts including a middle part of C8Benz and two parts of TC14 aggregation at both ends of rodlike RMs, which is regarded as the origin of RMs shape transition. Further, the analysis of free energy for RMs fusion indicates that the high fusion ability of C8Benz aggregation drives the formation of the dumbbell-like RMs. Accordingly, enhancing the affinity of the C8Benz is found to be effective strategy to further fusion of rodlike RMs in end-to-end manner, yielding a wormlike RMs with a beads-on-a-string structure. It is expected that this work will provide a valuable information for design the hydrocarbon wormlike RMs and facilitate the potential application of scCO2.
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Affiliation(s)
- Muhan Wang
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
| | - Timing Fang
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
| | - Pan Wang
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
| | - Youguo Yan
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
| | - Jun Zhang
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
| | - Bing Liu
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
| | - Xiaoli Sun
- College of Science and ‡Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong, China University of Petroleum , 266580 Qingdao, Shandong, China
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Peach J, Czajka A, Hazell G, Hill C, Mohamed A, Pegg JC, Rogers SE, Eastoe J. Tuning Micellar Structures in Supercritical CO 2 Using Surfactant and Amphiphile Mixtures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:2655-2663. [PMID: 28215094 DOI: 10.1021/acs.langmuir.7b00324] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
For equivalent micellar volume fraction (ϕ), systems containing anisotropic micelles are generally more viscous than those comprising spherical micelles. Many surfactants used in water-in-CO2 (w/c) microemulsions are fluorinated analogues of sodium bis(2-ethylhexyl) sulfosuccinate (AOT): here it is proposed that mixtures of CO2-philic surfactants with hydrotropes and cosurfactants may generate elongated micelles in w/c systems at high-pressures (e.g., 100-400 bar). A range of novel w/c microemulsions, stabilized by new custom-synthesized CO2-phillic, partially fluorinated surfactants, were formulated with hydrotropes and cosurfactant. The effects of water content (w = [water]/[surfactant]), surfactant structure, and hydrotrope tail length were all investigated. Dispersed water domains were probed using high pressure small-angle neutron scattering (HP-SANS), which provided evidence for elongated reversed micelles in supercritical CO2. These new micelles have significantly lower fluorination levels than previously reported (6-29 wt % cf. 14-52 wt %), and furthermore, they support higher water dispersion levels than other related systems (w = 15 cf. w = 5). The intrinsic viscosities of these w/c microemulsions were estimated based on micelle aspect ratio; from this value a relative viscosity value can be estimated through combination with the micellar volume fraction (ϕ). Combining these new results with those for all other reported systems, it has been possible to "map" predicted viscosity increases in CO2 arising from elongated reversed micelles, as a function of surfactant fluorination and micellar aspect ratio.
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Affiliation(s)
- Jocelyn Peach
- School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom
| | - Adam Czajka
- School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom
| | - Gavin Hazell
- School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom
| | - Christopher Hill
- School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom
| | - Azmi Mohamed
- Faculty of Science and Mathematics, Department of Chemistry, University Pendidikan Sultan Idris , Tanjong Malim 35900, Perak, Malaysia
| | - Jonathan C Pegg
- School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom
| | - Sarah E Rogers
- Rutherford Appleton Laboratory, ISIS Spallation Source, Chilton, Oxfordshire, OX11 0QT, United Kingdom
| | - Julian Eastoe
- School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom
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Liu B, Tang X, Fang W, Li X, Zhang J, Zhang Z, Shen Y, Yan Y, Sun X, He J. Molecular dynamics study of di-CF4 based reverse micelles in supercritical CO 2. Phys Chem Chem Phys 2016; 18:29156-29163. [PMID: 27730238 DOI: 10.1039/c6cp04253h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Reverse micelles (RMs) in supercritical CO2 (scCO2) are promising alternatives for organic solvents, especially when both polar and non-polar components are involved. Fluorinated surfactants, particularly double-chain fluorocarbon surfactants, are able to form well-structured RMs in scCO2. The inherent self-assembly mechanisms of surfactants in scCO2 are still subject to discussion. In this study, molecular dynamics simulations are performed to investigate the self-aggregation behavior of di-CF4 based RMs in scCO2, and stable and spherical RMs are formed. The dynamics process and the self-assembly structure in the RMs reveal a three-step mechanism to form the RMs, that is, small RMs, rod-like RMs and fusion of the rod-like RMs. Hydrogen-bonds between headgroups and water molecules, and salt bridges linking Na+ ions, headgroups and water molecules enhance the interfacial packing efficiency of the surfactant. The results show that di-CF4 molecules have a high surfactant coverage at the RM interface, implying a high CO2-philicity. This mainly results from bending of the short chain (C-COO-CH2-(CF2)3-CF3) due to the flexible carboxyl group. The microscopic insight provided in this study is helpful in understanding surfactant self-assembly phenomena and designing new CO2-philic surfactants.
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Affiliation(s)
- Bing Liu
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China. and NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, 7491, Norway.
| | - Xinpeng Tang
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Wenjing Fang
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Xiaoqi Li
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Jun Zhang
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Zhiliang Zhang
- NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, 7491, Norway.
| | - Yue Shen
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Youguo Yan
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Xiaoli Sun
- School of Science, China University of Petroleum, Qingdao 266580, Shandong, China.
| | - Jianying He
- NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, 7491, Norway.
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Wang JS, Wai CM, Yak HK, Chiu KH. Influence of the characteristics of a water-in-CO 2 microemulsion on the separation of metal species. SEP SCI TECHNOL 2016. [DOI: 10.1080/01496395.2016.1185443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
| | - Chien M. Wai
- Department of Chemistry, University of Idaho, Moscow, Idaho, USA
| | - Hwa-Kwang Yak
- Department of Chemistry, Chung Yuan Christian University, Chung Li, Taiwan, ROC
| | - Kong-Hwa Chiu
- Department of Chemistry, National Dong Hwa University, Shoufeng, Hualien, Taiwan, ROC
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