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Kawano M, Sadakane K, Iwase H, Matsugami M, Marekha BA, Idrissi A, Takamuku T. Assessment of the UCST-type liquid-liquid phase separation mechanism of imidazolium-based ionic liquid, [C 8mim][TFSI], and 1,4-dioxane by SANS, NMR, IR, and MD simulations. Phys Chem Chem Phys 2021; 23:24449-24463. [PMID: 34697615 DOI: 10.1039/d1cp01940f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Liquid-liquid phase separation of binary systems for imidazolium-based ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI], where n represents the alkyl chain length of the cation), with 1,4-dioxane (1,4-DIO) was observed as a function of temperature and 1,4-DIO mole fraction, x1,4-DIO. The phase diagrams obtained for [Cnmim][TFSI]-1,4-DIO systems showed that the miscible region becomes wider with an increase in the alkyl chain length, n. For n = 6 and 8, an upper critical solution temperature (UCST) was found. To clarify the mechanism of the UCST-type phase separation, small-angle neutron scattering (SANS) experiments were conducted on the [C8mim][TFSI]-1,4-DIO-d8 system at several x1,4-DIO. The critical exponents of γ and ν determined from the SANS experiments showed that phase separation of the system at the UCST mole fraction occurs via the 3D-Ising mechanism, while that on both sides of UCST occurs via the mean field mechanism. Thus, the crossover of mechanism was observed for this system. The microscopic interactions among the cation, anion, and 1,4-DIO were elucidated using 1H and 13C NMR and IR spectroscopic techniques, together with the theoretical method of molecular dynamics (MD) simulations. The results on the microscopic interactions suggest that 1,4-DIO molecules cannot strongly interact with H atoms on the imidazolium ring, while they interact with the octyl chain of the cation through dispersion force. With a decrease in temperature, 1,4-DIO molecules gradually aggregate to form 1,4-DIO clusters in the binary solutions. The strengthening of the C-H⋯O interaction between 1,4-DIO molecules by cooling is the key to the phase separation. Of course, the electrostatic interaction between the cations and anions results in the formation of IL clusters. When IL clusters are excluded from 1,4-DIO clusters, liquid-liquid phase separation occurs. Accordingly, the balance between the electrostatic force between the cations and anions and the C-H⋯O interaction between the 1,4-DIO determines the 3D-Ising or the mean field mechanism of phase separation.
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Affiliation(s)
- Masahiro Kawano
- Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan
| | - Koichiro Sadakane
- Faculty of Life and Medical Sciences, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
| | - Hiroki Iwase
- Comprehensive Research Organization for Science and Society (CROSS), 162-1 Shirakata, Tokai, Ibaraki 319-1106, Japan
| | - Masaru Matsugami
- Faculty of Liberal Arts, National Institute of Technology (KOSEN), Kumamoto College, 2659-2 Suya, Koshi, Kumatomo 861-1102, Japan
| | - Bogdan A Marekha
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, 29 Jahnstr., 69230 Heidelberg, Germany
| | - Abdenacer Idrissi
- University of Lille, CNRS, UMR 8516 -LASIRe- Laboratoire Avancé de Spectroscopie pour les Interactions la Réactivité et l'environnement, F-5900 Lille, France
| | - Toshiyuki Takamuku
- Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan.
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Thermodynamics of amine mixtures. Systems formed by alkyl-amine and ether, or N,N-dialkylamide, or ethanenitrile. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.112907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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