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Emerson MS, Ogbodo R, Margulis CJ. Spiers Memorial Lecture: From cold to hot, the structure and structural dynamics of dense ionic fluids. Faraday Discuss 2024. [PMID: 39045616 DOI: 10.1039/d4fd00086b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2024]
Abstract
The structure of ionic liquids (ILs), which a decade or two ago was the subject of polite but heated debate, is now much better understood. This has opened opportunities to ask more sophisticated questions about the role of structure in transport, the structure of systems with ions that are not prototypical, and the similarity between ILs and other dense ionic fluids such as the high-temperature inorganic molten salts; let alone the fact that new areas of research have emerged that sprung from our collective understanding of the structure of ILs such as the deep eutectic solvents, the polymerized ionic liquids, and the zwitterionic liquids. Yet, our understanding of the structure of prototypical ILs may not be as complete as we think it to be, given that recent experiments appear to show that in some cases there may be more than one liquid phase resulting in liquid-liquid (L-L) phase transitions. This article presents a perspective on what we think are key topics related to the structure and structural dynamics of ILs and to some extent high-temperature molten salts.
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Affiliation(s)
- Matthew S Emerson
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
| | - Raphael Ogbodo
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
| | - Claudio J Margulis
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
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2
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Philippi F, Rauber D, Palumbo O, Goloviznina K, McDaniel J, Pugh D, Suarez S, Fraenza CC, Padua A, Kay CWM, Welton T. Flexibility is the key to tuning the transport properties of fluorinated imide-based ionic liquids. Chem Sci 2022; 13:9176-9190. [PMID: 36093026 PMCID: PMC9384794 DOI: 10.1039/d2sc03074h] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 07/02/2022] [Indexed: 11/21/2022] Open
Abstract
Ionic liquids are becoming increasingly popular for practical applications such as biomass processing and lithium-ion batteries. However, identifying ionic liquids with optimal properties for specific applications by trial and error is extremely inefficient since there are a vast number of potential candidate ions. Here we combine experimental and computational techniques to determine how the interplay of fluorination, flexibility and mass affects the transport properties of ionic liquids with the popular imide anion. We observe that fluorination and flexibility have a large impact on properties such as viscosity, whereas the influence of mass is negligible. Using targeted modifications, we show that conformational flexibility provides a significant contribution to the success of fluorination as a design element. Contrary to conventional wisdom, fluorination by itself is thus not a guarantor for beneficial properties such as low viscosity.
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Affiliation(s)
- Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| | - Daniel Rauber
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany
| | - Oriele Palumbo
- Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi Piazzale Aldo Moro 5 00185 Rome Italy
| | | | - Jesse McDaniel
- School of Chemistry and Biochemistry, Georgia Institute of Technology Atlanta Georgia 30332-0400 USA
| | - David Pugh
- Department of Chemistry, King's College London 7 Trinity Street London SE1 1DB UK
| | - Sophia Suarez
- Department of Physics, Brooklyn College of CUNY Brooklyn New York 11210 USA
| | - Carla C Fraenza
- Department of Physics and Astronomy, Hunter College of CUNY New York 10065 USA
| | - Agilio Padua
- Laboratoire de Chimie, École Normale Supérieure de Lyon, CNRS 69364 Lyon France
| | - Christopher W M Kay
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany
- London Centre for Nanotechnology, University College London 17-19 Gordon Street London WC1H 0AH UK
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
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3
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Yamaguchi T. Coupling between Translational Diffusion of a Solute and Dynamics of the Heterogeneous Structure: Higher Alcohols and Ionic Liquids. J Phys Chem B 2022; 126:3125-3134. [PMID: 35438995 DOI: 10.1021/acs.jpcb.2c01053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Translational diffusion of nonpolar monoatomic solutes in a room-temperature ionic liquid and 1-octanol was studied by molecular dynamics simulation. The diffusion coefficient was evaluated in two different ways: (1) from the mean-square displacement of a freely diffusing solute and (2) from the time correlation function of force acting on a fixed solute. The diffusion of the free solute is much greater than the prediction of the Stokes-Einstein (SE) relation when the size of the solute is small, as has been reported by many experimental works. In contrast, the friction on fixed small solutes follows the SE relation. The mechanism of the solute diffusion in both solvents was then analyzed based on the coupling between the translational motion of the solute and the collective dynamics of the heterogeneous intermediate-range structure characteristic to these solvents. Analysis revealed that the coupling is present in all systems, but the relaxation is fast in the cases of free and small solutes. This suggests that the coupling can relax through the motion of the solute when the solute is free and small, while the relaxation of the heterogeneous structure itself is required for large or fixed solutes. The difference in the relaxation dynamics of the friction on the solute and the shear viscosity is explained as the coupling with different dynamic modes of the solvent. Therefore, the validity of the SE relation may not be a good criterion to judge whether the mechanisms of the diffusion and the viscosity are the same or not.
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Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
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4
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Philippi F, Rauber D, Eliasen KL, Bouscharain N, Niss K, Kay CWM, Welton T. Pressing matter: why are ionic liquids so viscous? Chem Sci 2022; 13:2735-2743. [PMID: 35340854 PMCID: PMC8890108 DOI: 10.1039/d1sc06857a] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Accepted: 02/06/2022] [Indexed: 01/09/2023] Open
Abstract
Room temperature ionic liquids are considered to have huge potential for practical applications such as batteries. However, their high viscosity presents a significant challenge to their use changing from niche to ubiquitous. The modelling and prediction of viscosity in ionic liquids is the subject of an ongoing debate involving two competing hypotheses: molecular and local mechanisms versus collective and long-range mechanisms. To distinguish between these two theories, we compared an ionic liquid with its uncharged, isoelectronic, isostructural molecular mimic. We measured the viscosity of the molecular mimic at high pressure to emulate the high densities in ionic liquids, which result from the Coulomb interactions in the latter. We were thus able to reveal that the relative contributions of coulombic compaction and the charge network interactions are of similar magnitude. We therefore suggest that the optimisation of the viscosity in room temperature ionic liquids must follow a dual approach.
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Affiliation(s)
- Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| | - Daniel Rauber
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany
| | - Kira Lieberkind Eliasen
- "Glass and Time", IMFUFA, Department of Science and Environment, Roskilde University P.O. Box 260 DK-4000 Roskilde Denmark
| | | | - Kristine Niss
- "Glass and Time", IMFUFA, Department of Science and Environment, Roskilde University P.O. Box 260 DK-4000 Roskilde Denmark
| | - Christopher W M Kay
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany.,London Centre for Nanotechnology, University College London 17-19 Gordon Street London WC1H 0AH UK
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
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5
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Amith WD, Araque JC, Margulis CJ. Relationship between the Relaxation of Ionic Liquid Structural Motifs and That of the Shear Viscosity. J Phys Chem B 2021; 125:6264-6271. [PMID: 34097825 PMCID: PMC8279556 DOI: 10.1021/acs.jpcb.1c03105] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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In a set of recent
articles, we have highlighted that friction
is highly inhomogeneous in a typical ionic liquid (IL) with charge
networks that are stiff and charge-depleted regions that are soft.
This has consequences not only for the dynamics of ILs but also for the transport properties of solutes
dissolved in them. In this article, we explore whether the family
of alkylimidazolium ILs coupled with bis(trifluoromethylsulfonyl)imide
(with similar Coulombic interactions but different alkyl tails), when
dynamically “equalized” by having a similar shear viscosity,
display q-dependent structural relaxation time scales
that are the same across the family. Our results show that this is
not the case, and in fact, the relaxation of in-network charge alternation
appears to be significantly affected by the presence of separate polar
and apolar domains. However, we also find that if one was to assign
weight factors to the relaxation of the structural motifs, charge
alternation always contributes about the same amount (between 62.1
and 66.3%) across systems to the running integral of the stress tensor
correlation function from which the shear viscosity is derived. Adjacency
correlations between positive and negative moieties also contribute
an identical amount if a prepeak is not present (about 38%) and a
slightly smaller amount (about 28%) when intermediate range order
exists. The prepeak only contributes about 6% to viscoelastic relaxation,
highlighting that the dynamics of the smaller scale motifs is the
most important.
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Affiliation(s)
| | - Juan C Araque
- School of Engineering, Benedictine College, Atchison, Kansas 66002, United States
| | - Claudio J Margulis
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
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6
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Amith WD, Araque JC, Margulis CJ. A Pictorial View of Viscosity in Ionic Liquids and the Link to Nanostructural Heterogeneity. J Phys Chem Lett 2020; 11:2062-2066. [PMID: 32079397 DOI: 10.1021/acs.jpclett.0c00170] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Prototypical ionic liquids (ILs) are characterized by three structural motifs associated with (1) vicinal interactions, (2) the formation of positive-negative charge-alternating chains or networks, and (3) the alternation of these networks with apolar domains. In recent articles, we highlighted that the friction and mobility in these systems are nowhere close to being spatially homogeneous. This results in what one could call mechanical heterogeneity, where charge networks are intrinsically stiff and charge-depleted regions are softer, flexible, and mobile. This Letter attempts to provide a clear and visual connection between friction-associated with the dynamics of the structural motifs (in particular, the charge network)-and recent theoretical work by Yamaguchi linking the time-dependent viscosity of ILs to the decay of the charge alternation peak in the dynamic structure function. We propose that charge blurring associated with the loss of memory of where positive and negative charges are within networks is the key mechanism associated with viscosity in ILs. An IL will have low viscosity if a characteristic charge-blurring decorrelation time is low. With this in mind, engineering new low-viscosity ILs is reduced to understanding how to minimize this quantity.
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Affiliation(s)
| | - Juan C Araque
- School of Engineering, Benedictine College, Atchison, Kansas 66002, United States
| | - Claudio J Margulis
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
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Yamaguchi T, Faraone A, Nagao M. Collective Mesoscale Dynamics of Liquid 1-Dodecanol Studied by Neutron Spin-Echo Spectroscopy with Isotopic Substitution and Molecular Dynamics Simulation. J Phys Chem B 2019; 123:239-246. [PMID: 30511874 PMCID: PMC11168703 DOI: 10.1021/acs.jpcb.8b10299] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The collective dynamics of liquid 1-dodecanol was investigated at a length scale matching the mesoscale structure arising from the segregation of hydrophilic and hydrophobic domains. To this end, neutron spin-echo experiments were performed on a series of partially deuterated samples and the relevant collective dynamics of the hydroxyl groups with respect to the alkyl chains was extracted from the linear combination of the intermediate scattering functions of these samples. The resulting collective dynamics is slower than the single particle dynamics as determined by the measurement on the nondeuterated sample. The experimental results are in excellent agreement with molecular dynamics simulation, which allows further insight into the mechanism of the molecular motions. The results indicate that two factors are responsible for the slower collective dynamics. The first one is the slower dynamics of the hydroxyl group, with respect to the alkyl chains, owing to hydrogen bonding, and the second one is the presence of mesoscale structuring.
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Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi 464-8603, Japan
| | - Antonio Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, United States
| | - Michihiro Nagao
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, United States
- Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408-1398, United States
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8
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Yamaguchi T. Stress-structure coupling and nonlinear rheology of Lennard-Jones liquid. J Chem Phys 2018; 148:234507. [DOI: 10.1063/1.5026536] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University, Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan
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9
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Yamaguchi T, Saito M, Yoshida K, Yamaguchi T, Yoda Y, Seto M. Structural Relaxation and Viscoelasticity of a Higher Alcohol with Mesoscopic Structure. J Phys Chem Lett 2018; 9:298-301. [PMID: 29290123 DOI: 10.1021/acs.jpclett.7b02907] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This work studied the slow dynamics of liquids with mesoscopic structure and its relation to shear viscosity. Quasielastic scattering measurements were made on a liquid higher alcohol, 3,7-dimethyl-1-octanol, using γ-ray time-domain interferometry at a synchrotron radiation facility, SPring-8. The quasielastic scattering spectra were measured to determine the structural relaxation at two wavenumbers of the prepeak and the main peak of the static structure factor. It was found that relaxation at the prepeak is more than 10 times slower than that at the main peak. Compared with the viscoelastic spectrum, which exhibits bimodal relaxation, the relaxations at the prepeak and the main peak were shown to correspond to the slower and faster modes of the viscoelastic relaxation, respectively. This indicates that the dynamics of the mesoscopic structure represented as the prepeak contributes to the shear viscosity through the slowest mode of the viscoelastic relaxation.
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Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University , Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan
| | - Makina Saito
- Research Reactor Institute, Kyoto University , Kumatori, Osaka 590-0494, Japan
| | - Koji Yoshida
- Department of Chemistry, Faculty of Science, Fukuoka University , Nanakuma, Jonan, Fukuoka 814-0180, Japan
| | - Toshio Yamaguchi
- Department of Chemistry, Faculty of Science, Fukuoka University , Nanakuma, Jonan, Fukuoka 814-0180, Japan
| | - Yoshitaka Yoda
- Research and Utilization Division, Japan Synchrotron Radiation Research Institute , Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Makoto Seto
- Research Reactor Institute, Kyoto University , Kumatori, Osaka 590-0494, Japan
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10
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Yamaguchi T, Yoshida K, Yamaguchi T, Nagao M, Faraone A, Seki S. Decoupling between the Temperature-Dependent Structural Relaxation and Shear Viscosity of Concentrated Lithium Electrolyte. J Phys Chem B 2017; 121:8767-8773. [PMID: 28841313 DOI: 10.1021/acs.jpcb.7b04633] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The intermediate scattering functions of concentrated solutions of LiPF6 in propylene carbonate (PC) were measured at various temperatures, two different wavenumbers, and three different concentrations using neutron spin echo (NSE) spectroscopy. The temperature dependence of the relaxation time was larger than that of the steady-state shear viscosity in all cases. The shear relaxation spectra were also determined at different temperatures. The normalized spectra reduced to a master curve when the frequency was multiplied by the steady-state shear viscosity, indicating that the temperature dependence of the steady-state shear viscosity can be explained by that of the relaxation time of the shear stress. It is thus suggested that the dynamics of the shear stress is decoupled from the structural dynamics on the molecular scale.
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Affiliation(s)
- Tsuyoshi Yamaguchi
- Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University , Furo-cho, Chikusa, Nagoya, Aichi 464-8603, Japan
| | - Koji Yoshida
- Department of Chemistry, Faculty of Science, Fukuoka University , Nanakuma, Jonan, Fukuoka 814-0180, Japan
| | - Toshio Yamaguchi
- Department of Chemistry, Faculty of Science, Fukuoka University , Nanakuma, Jonan, Fukuoka 814-0180, Japan
| | - Michihiro Nagao
- NIST Center for Neutron Research, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-6102, United States.,Center for Exploration of Energy and Matter, Indiana University , Bloomington, Indiana 47408-1398, United States
| | - Antonio Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology , Gaithersburg, Maryland 20899-6102, United States
| | - Shiro Seki
- Materials Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI) , 2-11-1, Iwado-kita, Komae, Tokyo 201-8511, Japan
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11
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Zorębski E, Zorębski M, Dzida M, Lodowski P, Kowalska-Szojda K, Mirzaev SZ, Kaatze U. Supramolecular structure fluctuations of an imidazolium-based protic ionic liquid. J Chem Phys 2017; 146:134505. [DOI: 10.1063/1.4979287] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Edward Zorębski
- Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland
| | - Michał Zorębski
- Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland
| | - Marzena Dzida
- Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland
| | - Piotr Lodowski
- Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland
| | | | - Sirojiddin Z. Mirzaev
- Department of Engineering Physics, Tashkent State Technical University, Do’rmon Yuli 33, 100125 Tashkent, Uzbekistan
- Universität Göttingen, Drittes Physikalisches Institut, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Udo Kaatze
- Universität Göttingen, Drittes Physikalisches Institut, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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12
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Yamaguchi T. Viscoelastic relaxations of high alcohols and alkanes: Effects of heterogeneous structure and translation-orientation coupling. J Chem Phys 2017. [DOI: 10.1063/1.4977705] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Tsuyoshi Yamaguchi
- Department of Molecular Design and Engineering, Graduate School of Engineering, Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan
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