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The charge transport mechanism in Brønsted-acidic protic ionic liquid/water systems – An NMR and QENS study. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.117712] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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2
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Mariani A, Bonomo M, Gao X, Centrella B, Nucara A, Buscaino R, Barge A, Barbero N, Gontrani L, Passerini S. The unseen evidence of Reduced Ionicity: The elephant in (the) room temperature ionic liquids. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2020.115069] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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3
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Overbeck V, Schröder H, Bonsa AM, Neymeyr K, Ludwig R. Insights into the translational and rotational dynamics of cations and anions in protic ionic liquids by means of NMR fast-field-cycling relaxometry. Phys Chem Chem Phys 2021; 23:2663-2675. [PMID: 33480888 DOI: 10.1039/d0cp05440b] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Understanding the translational and rotational dynamics of cations and anions in hydrogen bonded protic ionic liquids (PIls) is still a challenge. In this study, we determine self-diffusion coefficients and rotational correlation times of both ions in triethylammonium based PILs by means of NMR Fast-Field-Cycling (FFC) relaxometry. Global fits of 1H and 19F nuclear magnetic relaxation dispersion (NMRD) curves allowed proper separation into intra and inter molecular relaxation rates for both NMR sensitive nuclei and thus a reliable description of translational and rotational motion for both ions individually. The diffusion coefficients of the cations are in the order of 6 × 10-11 m2 s-1 at room temperature and about 50 per cent larger than those of the anions. The diffusion coefficients of cations and anions in both PILs were compared with those we derived from applying an universal dispersion power law and those known from pulsed field gradient (PFG) NMR studies. Considering the Nernst-Einstein equation, molar conductivities were calculated from cationic and anionic diffusion coefficients and related to directly measured molar conductivities, allowing the determination of the degree of dissociation. The rotational correlation times τR ranging from 50 ps up to 2 ns as a function of temperature were compared with those obtained from high-field NMR quadrupolar relaxation time measurements addressing explicitly the rotation of the NH vector and giving insights into the acidic proton mobility. The Stokes-Einstein and Stokes-Einstein-Debye relations were applied to relate the diffusion coefficients and rotational correlation times to the macroscopic bulk viscosity. The results were also discussed with respect to the archetypical PIL ethylammonium nitrate.
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Affiliation(s)
- Viviane Overbeck
- Department LL&M, University of Rostock, Albert-Einstein-Str. 25, 18059 Rostock, Germany. and Physical and Theoretical Chemistry, Department of Chemistry, University of Rostock, Dr-Lorenz-Weg 2, 18059 Rostock, Germany
| | - Henning Schröder
- Department of Mathematics, University of Rostock, Ulmenstr. 69, 18057 Rostock, Germany
| | - Anne-Marie Bonsa
- Department LL&M, University of Rostock, Albert-Einstein-Str. 25, 18059 Rostock, Germany. and Physical and Theoretical Chemistry, Department of Chemistry, University of Rostock, Dr-Lorenz-Weg 2, 18059 Rostock, Germany
| | - Klaus Neymeyr
- Department of Mathematics, University of Rostock, Ulmenstr. 69, 18057 Rostock, Germany
| | - Ralf Ludwig
- Department LL&M, University of Rostock, Albert-Einstein-Str. 25, 18059 Rostock, Germany. and Physical and Theoretical Chemistry, Department of Chemistry, University of Rostock, Dr-Lorenz-Weg 2, 18059 Rostock, Germany and Leibniz Institute for Catalysis e.V., Albert-Einstein-Str. 29a, 18059 Rostock, Germany
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4
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Liu S, Tyagi M, Akcora P. Polymer-Coupled Local Dynamics Enhances Conductivity of Ionic Liquids. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01434] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Siqi Liu
- Department of Chemical Engineering & Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, United States
| | - Madhusudan Tyagi
- NIST Center for Neutron Research, 100 Bureau Dr, Gaithersburg, Maryland 20899, United States
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Pinar Akcora
- Department of Chemical Engineering & Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, United States
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5
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Hasani M, Varela LM, Martinelli A. Short-Range Order and Transport Properties in Mixtures of the Protic Ionic Liquid [C 2HIm][TFSI] with Water or Imidazole. J Phys Chem B 2020; 124:1767-1777. [PMID: 31999926 DOI: 10.1021/acs.jpcb.9b10454] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We investigate the effect of adding different molecular cosolvents, water or imidazole, to the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide, i.e., [C2HIm][TFSI]. We explore how the added cosolvent distributes within the ionic liquid by means of molecular dynamics simulations and X-ray scattering. We also analyze the degree of short-range heterogeneity in the resulting mixtures, finding that while imidazole easily mixes with the protic ionic liquid, water tends to form small clusters in its own water-rich domains. These differences are rationalized by invoking the nature of intermolecular interactions. In aqueous mixtures water-water hydrogen bonds are more likely to form than water-ion hydrogen bonds (water-TFSI bonds being particularly weak), while imidazole can interact with both cations and anions. Hence, the cation-anion association is negligibly influenced by the presence of water, whereas the addition of imidazole creates solvent-separated ion pairs and is thus able to also increase the ionicity. As a consequence of these structural and interactional features, transport properties like self-diffusion and ionic conductivity also show different composition dependencies. While the mobility of both ions and solvent is increased considerably by the addition of water, upon adding imidazole this property changes significantly only for molar fractions of imidazole above 0.6. At these molar fractions, which correspond to a base-excess composition, the imidazole/[C2HIm][TFSI] mixture behaves as a glass-forming liquid with suppressed phase transitions, while homomixtures such as imidazole/[HIm][TFSI] can display a eutectic point.
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Affiliation(s)
- Mohammad Hasani
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden
| | - Luis Miguel Varela
- Department of Applied and Particle Physics, University of Santiago de Compostela, Santiago de Compostela, Spain
| | - Anna Martinelli
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden
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6
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Mora Cardozo JF, Embs JP, Benedetto A, Ballone P. Equilibrium Structure, Hydrogen Bonding, and Proton Conductivity in Half-Neutralized Diamine Ionic Liquids. J Phys Chem B 2019; 123:5608-5625. [PMID: 30875220 DOI: 10.1021/acs.jpcb.9b00890] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Recent experiments on proton conducting ionic liquids point to half-neutralized diamine-triflate salts as promising candidates for applications in power generation and energy conversion electrochemical devices. Structural and dynamical properties of the simplest among these compounds are investigated by a combination of density functional theory (DFT) and molecular dynamics (MD) simulations based on an empirical force field. Three different cations have been considered, consisting of a pair of amine-ammonium terminations joined by a short aliphatic segment -(CH2) n- with n = 2, 3, and 4. First, the ground state structure, vibrational eigenstates, and hydrogen-bonding properties of single ions, neutral ion pairs, small neutral aggregates of up to eight ions, and molecularly thin hydrogen bonded wires have been investigated by DFT computations. Second, structural and dynamical properties of homogeneous liquid and amorphous phases are investigated by MD simulations over the temperature range of 200 ≤ T ≤ 440 K. Structure factors, radial distribution functions, diffusion coefficient, and electrical conductivity are computed and discussed, highlighting the inherent structural heterogeneity of these compounds. The core investigation, however, is the characterization of connected paths consisting of cation chains that could support proton transport via a Grotthuss-type mechanism. Since simulations are carried out using a force field of fixed bonding topology, this analysis is based on the equilibrium structure only, using geometrical criteria to identify potential paths for proton conduction. Paths of connected cations can reach a length of 80 cations and 30 Å, provided that bridging oxygen atoms from triflate anions are taken into account. The effects of water contamination at 1% weight concentration on the structure, dynamics, and paths for proton transport are discussed.
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Affiliation(s)
- Juan F Mora Cardozo
- Laboratory for Neutron Scattering and Imaging , Paul Scherrer Institute , Villigen PSI, Villigen 5232 , Switzerland
| | - J P Embs
- Laboratory for Neutron Scattering and Imaging , Paul Scherrer Institute , Villigen PSI, Villigen 5232 , Switzerland
| | - A Benedetto
- Laboratory for Neutron Scattering and Imaging , Paul Scherrer Institute , Villigen PSI, Villigen 5232 , Switzerland.,Department of Sciences , University of Roma Tre , Via della Vasca Navale 84 , 00146 Rome , Italy
| | - P Ballone
- Italian Institute of Technology , Via Morego 30 , 16163 Genova , Italy
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7
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Watanabe H, Umecky T, Arai N, Nazet A, Takamuku T, Harris KR, Kameda Y, Buchner R, Umebayashi Y. Possible Proton Conduction Mechanism in Pseudo-Protic Ionic Liquids: A Concept of Specific Proton Conduction. J Phys Chem B 2019; 123:6244-6252. [DOI: 10.1021/acs.jpcb.9b03185] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Hikari Watanabe
- Graduate School of Science and Technology, Niigata University, 8050 Ikarashi, 2-no-cho, Nishi-ku, Niigata City 950-2181, Japan
| | - Tatsuya Umecky
- Graduate School of Science and Engineering, Saga University, 1 Honjo-machi, Saga 840-8502, Japan
| | - Nana Arai
- Graduate School of Science and Technology, Niigata University, 8050 Ikarashi, 2-no-cho, Nishi-ku, Niigata City 950-2181, Japan
| | - Andreas Nazet
- Institute of Theoretical and Physical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany
| | - Toshiyuki Takamuku
- Graduate School of Science and Engineering, Saga University, 1 Honjo-machi, Saga 840-8502, Japan
| | - Kenneth R. Harris
- School of Science, The University of New South Wales, P.O. Box 7916, Canberra BC, Australian Capital Territory 2610, Australia
| | - Yasuo Kameda
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata City, Yamagata 990-8560, Japan
| | - Richard Buchner
- Institute of Theoretical and Physical Chemistry, University of Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany
| | - Yasuhiro Umebayashi
- Graduate School of Science and Technology, Niigata University, 8050 Ikarashi, 2-no-cho, Nishi-ku, Niigata City 950-2181, Japan
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8
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Linking Structure to Dynamics in Protic Ionic Liquids: A Neutron Scattering Study of Correlated and Single-Particle Motions. Sci Rep 2018; 8:16400. [PMID: 30401950 PMCID: PMC6219547 DOI: 10.1038/s41598-018-34481-w] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 10/18/2018] [Indexed: 11/22/2022] Open
Abstract
Coupling between dynamical heterogeneity of ionic liquids and their structural periodicity on different length-scales can be directly probed by quasielastic neutron scattering with polarization analysis. The technique provides the tools to investigate single-particle and cooperative ion motions separately and, thus, dynamics of ion associations affecting the net charge transport can be experimentally explored. The focus of this study is the structure-dynamic relationship in the protic ionic liquid, triethylammonium triflate, characterized by strong hydrogen bonds between cations and anions. The site-selective deuterium/hydrogen-isotope substitution was applied to modulate the relative contributions of different atom groups to the total coherent and incoherent scattering signal. This approach in combination with molecular dynamics simulations allowed us to obtain a sophisticated description of cation self-diffusion and confined ion pair dynamics from the incoherent spectral component by using the acidic proton as a tagged particle. The coherent contribution of the neutron spectra demonstrated substantial ion association leading to collective ion migration that preserves charge alteration on picosecond time scale, as well as correlation of the localized dynamics occurring between adjacent ions.
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9
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Yaghini N, Abdurrokhman I, Hasani M, Martinelli A. Transport properties and intermolecular interactions in binary mixtures based on the protic ionic liquid ethylimidazolium triflate and ethylene glycol. Phys Chem Chem Phys 2018; 20:22980-22986. [PMID: 30156221 DOI: 10.1039/c8cp03093f] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The binary mixture based on the protic ionic liquid (PIL) ethylimidazolium triflate (C2HImTfO) and the diol compound ethylene glycol (EG) has been investigated in the whole composition range from pure PIL to pure EG. At 30 °C the addition of EG increases both the ionic conductivity and the self-diffusivity of the ions. These quantities, however, change at different rates suggesting that the ionicity of the system is composition dependent. This behaviour is explained by means of new intermolecular forces established when a second compound like EG is introduced into the ionic network. More specifically, a complex H-bonded network is formed that involves the -NH group of the cation, the -OH group of EG and the -SO3 group of the anion. This configuration may increase the fluidity of the mixture but not necessarily the ionic dissociation. Moreover, diffusion NMR results indicate the occurrence of local proton dynamics, which arise from a proton exchange between the -NH of the cation and the -OH of EG, providing the requisite for a long-range Grotthuss mechanism of proton transport.
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Affiliation(s)
- Negin Yaghini
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
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10
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Yaghini N, Gómez-González V, Varela LM, Martinelli A. Structural origin of proton mobility in a protic ionic liquid/imidazole mixture: insights from computational and experimental results. Phys Chem Chem Phys 2018; 18:23195-206. [PMID: 27499376 DOI: 10.1039/c6cp03058k] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The structure, dynamics, and phase behavior of a binary mixture based on the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide (C2HImTFSI) and imidazole are investigated by (1)H NMR spectroscopy, vibrational spectroscopy, diffusion NMR, calorimetric measurements, and molecular dynamics simulations. Particular attention is given to the nature of the H-bonds established and the consequent occurrence of the Grotthuss mechanism of proton transfer. We find that due to their structural similarity, the imidazolium cation and the imidazole molecule behave as interchangeable and competing sites of interaction for the TFSI anion. All investigated properties, that is the phase behavior, strength of ion-ion and ion-imidazole interactions, number of specific H-bonds, density, and self-diffusivity, are composition dependent and show trend changes at mole fractions of imidazole (χ) approximately equal to 0.2 and 0.5. Beyond χ = 0.8 imidazole is not miscible in C2HImTFSI at room temperature. We find that at the equimolar composition (χ ≈ 0.5) a structural transition occurs from an ionic network mainly stabilized by coulombic forces to a mixed phase held together by site specific H-bonds. The same composition also marks a steeper decrease in density and increase in diffusivity, resulting from the preference of imidazole molecules to H-bond to each other in a chain-like manner. As a result of these structural features the Grotthuss mechanism of proton transfer is less favored at the equimolar composition where H-bonds are too stable. By contrast, the Grotthuss mechanism is more pronounced in the low concentration range where imidazole acts as a base pulling the proton of the imidazolium cation. At high imidazole concentrations the contribution from the vehicular mechanism dominates.
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Affiliation(s)
- Negin Yaghini
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
| | - Víctor Gómez-González
- Grupo de Nanomateriales, Fotonica y Materia Blanda, Departamento de Física de la Materia Condensada, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
| | - Luis M Varela
- Grupo de Nanomateriales, Fotonica y Materia Blanda, Departamento de Física de la Materia Condensada, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
| | - Anna Martinelli
- Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
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11
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Khudozhitkov AE, Stange P, Bonsa AM, Overbeck V, Appelhagen A, Stepanov AG, Kolokolov DI, Paschek D, Ludwig R. Dynamical heterogeneities in ionic liquids as revealed from deuteron NMR. Chem Commun (Camb) 2018; 54:3098-3101. [DOI: 10.1039/c7cc09440j] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Deuteron NMR spectroscopy is a suitable method to study dynamical heterogeneities in protic ionic liquids. In the 2H spectra of the protic ionic liquid [TEA][OTf] we observe anisotropic and isotropic signals at the same time.
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Affiliation(s)
- Alexander E. Khudozhitkov
- Boreskov Institute of Catalysis
- Siberian Branch of Russian Academy of Sciences
- Prospekt Akademika Lavrentieva 5
- Novosibirsk 630090
- Russia
| | - Peter Stange
- Universität Rostock
- Institut für Chemie
- Abteilung für Physikalische Chemie
- Dr-Lorenz-Weg 2
- 18059 Rostock
| | - Anne-Marie Bonsa
- Universität Rostock
- Institut für Chemie
- Abteilung für Physikalische Chemie
- Dr-Lorenz-Weg 2
- 18059 Rostock
| | - Viviane Overbeck
- Universität Rostock
- Institut für Chemie
- Abteilung für Physikalische Chemie
- Dr-Lorenz-Weg 2
- 18059 Rostock
| | - Andreas Appelhagen
- Universität Rostock
- Institut für Chemie
- Abteilung für Physikalische Chemie
- Dr-Lorenz-Weg 2
- 18059 Rostock
| | - Alexander G. Stepanov
- Boreskov Institute of Catalysis
- Siberian Branch of Russian Academy of Sciences
- Prospekt Akademika Lavrentieva 5
- Novosibirsk 630090
- Russia
| | - Daniil I. Kolokolov
- Boreskov Institute of Catalysis
- Siberian Branch of Russian Academy of Sciences
- Prospekt Akademika Lavrentieva 5
- Novosibirsk 630090
- Russia
| | - Dietmar Paschek
- Universität Rostock
- Institut für Chemie
- Abteilung für Physikalische Chemie
- Dr-Lorenz-Weg 2
- 18059 Rostock
| | - Ralf Ludwig
- Universität Rostock
- Institut für Chemie
- Abteilung für Physikalische Chemie
- Dr-Lorenz-Weg 2
- 18059 Rostock
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12
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Mora Cardozo JF, Burankova T, Embs JP, Benedetto A, Ballone P. Density Functional Computations and Molecular Dynamics Simulations of the Triethylammonium Triflate Protic Ionic Liquid. J Phys Chem B 2017; 121:11410-11423. [PMID: 29185753 DOI: 10.1021/acs.jpcb.7b10373] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Systematic molecular dynamics simulations based on an empirical force field have been carried out for samples of triethylammonium trifluoromethanesulfonate (triethylammonium triflate, [TEA][Tf]), covering a wide temperature range 200 K ≤ T ≤ 400 K and analyzing a broad set of properties, from self-diffusion and electrical conductivity to rotational relaxation and hydrogen-bond dynamics. The study is motivated by recent quasi-elastic neutron scattering and differential scanning calorimetry measurements on the same system, revealing two successive first order transitions at T ≈ 230 and 310 K (on heating), as well as an intriguing and partly unexplained variety of subdiffusive motions of the acidic proton. Simulations show a weakly discontinuous transition at T = 310 K and highlight an anomaly at T = 260 K in the rotational relaxation of ions that we identify with the simulation analogue of the experimental transition at T = 230 K. Thus, simulations help identifying the nature of the experimental transitions, confirming that the highest temperature one corresponds to melting, while the one taking place at lower T is a transition from the crystal, stable at T ≤ 260 K, to a plastic phase (260 ≤ T ≤ 310 K), in which molecules are able to rotate without diffusing. Rotations, in particular, account for the subdiffusive motion seen at intermediate T both in the experiments and in the simulation. The structure, distribution, and strength of hydrogen bonds are investigated by molecular dynamics and by density functional computations. Clustering of ions of the same sign and the effect of contamination by water at 1% wgt concentration are discussed as well.
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Affiliation(s)
- Juan F Mora Cardozo
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Villigen 5232, Switzerland
| | - T Burankova
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Villigen 5232, Switzerland
| | - J P Embs
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Villigen 5232, Switzerland
| | - A Benedetto
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Villigen 5232, Switzerland.,School of Chemistry, University College Dublin , Belfield, Dublin 4, Ireland.,School of Physics, University College Dublin , Belfield, Dublin 4, Ireland
| | - P Ballone
- Italian Institute of Technology , Via Morego 30, 16163 Genova, Italy
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13
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Han Q, Wang X, Byrne N. A Simple Approach to Achieve Self‐Buffering Protic Ionic Liquid‐Water Mixtures. ChemistrySelect 2017. [DOI: 10.1002/slct.201700651] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Qi Han
- Institute for Frontier Materials Deakin University Pigdons Road Waurn Ponds Victoria 3217 Australia
| | - Xungai Wang
- Institute for Frontier Materials Deakin University Pigdons Road Waurn Ponds Victoria 3217 Australia
| | - Nolene Byrne
- Institute for Frontier Materials Deakin University Pigdons Road Waurn Ponds Victoria 3217 Australia
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14
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Russina O, Triolo A. Ionic Liquids and Neutron Scattering. NEUTRON SCATTERING - APPLICATIONS IN BIOLOGY, CHEMISTRY, AND MATERIALS SCIENCE 2017. [DOI: 10.1016/b978-0-12-805324-9.00004-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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15
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Burankova T, Simeoni G, Hempelmann R, Mora Cardozo JF, Embs JP. Dynamic Heterogeneity and Flexibility of the Alkyl Chain in Pyridinium-Based Ionic Liquids. J Phys Chem B 2016; 121:240-249. [PMID: 27995787 DOI: 10.1021/acs.jpcb.6b10235] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Changing the number of carbon atoms in the substituents of ionic liquids (ILs) is a way to shift the balance between Coulomb and van der Waals forces and, thus, to tune physicochemical properties. Here we address this topic on the microscopic level by employing quasielastic neutron scattering (QENS) and provide information about the stochastic ionic motions in the N-alkylpyridinium based ILs in a relatively expanded time range, from short time (subpicosecond) particle rattling to long time diffusive regime (hundreds of picoseconds). We have systematically investigated the effect of the alkyl chain length on the picosecond dynamics by employing partial deuteration of the samples and varying the number of carbon atoms in the alkyl substituent. The localized dynamics of the side groups have appeared to be enhanced for bulkier cations, which is opposite to the trend observed for the translational motion. This result highlights the role of the conformational flexibility of the alkyl group on the dynamical properties of ILs.
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Affiliation(s)
- Tatsiana Burankova
- Department of Physical Chemistry, Saarland University , Saarbrücken, Germany.,Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Switzerland
| | - Giovanna Simeoni
- Heinz Maier-Leibnitz Zentrum and Physics Department, Technical University of Munich , Garching, Germany
| | - Rolf Hempelmann
- Department of Physical Chemistry, Saarland University , Saarbrücken, Germany
| | - Juan F Mora Cardozo
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Switzerland
| | - Jan P Embs
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute , Villigen PSI, Switzerland
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16
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Kumar Sahu P, Ghosh A, Sarkar M. Understanding Structure-Property Correlation in Monocationic and Dicationic Ionic Liquids through Combined Fluorescence and Pulsed-Field Gradient (PFG) and Relaxation NMR Experiments. J Phys Chem B 2015; 119:14221-35. [PMID: 26447540 DOI: 10.1021/acs.jpcb.5b07357] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Steady state, time-resolved fluorescence and NMR experiments are carried out to gain deeper insights into the structure-property correlation in structurally similar monocationic and dicationic room-temperature ionic liquids (RTILs). The excitation wavelength dependent fluorescence response of fluorophore in 1-methy-3-propyllimidazolium bis(trifluoromethylsulfonyl)amide [C3MIm][NTf2] is found to be different from that of 1,6-bis(3-methylimidazolium-1-yl)hexane bis(trifluoromethylsulfonyl)amide [C6(MIm)2][NTf2]2 and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide [C6MIm][NTf2]. The outcomes of the present solvent dynamics study in [C3MIm][NTf2] when compared with those in [C6(MIm)2][NTf2]2 and in [C6MIm][NTf2] from our previous studies (Phys. Chem. Chem. Phys. 2014, 16, 12918-12928) indicate the involvement of dipolar rotation of imidazolium cation during solvation. To correlate the findings of solvation dynamics study with the dipolar rotation of the imidazolium ring, pulsed-field gradient (PFG)-NMR technique for translational diffusion coefficient measurement and (1)H as well as (19)F spin-lattice relaxation measurements are employed. NMR investigation reveals that an ultrafast component of solvation can be related to the dipolar rotation of imidazolium cation; hence, the role of dipolar rotation of cations in governing the dynamics of solvation in ILs cannot be ignored. Analysis of the rotational relaxation dynamics data by the Stokes-Einstein-Debye hydrodynamic theory unveils distinctive features of solute-solvent interaction in [C3MIm][NTf2] and [C6(MIm)2][NTf2]2.
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Affiliation(s)
- Prabhat Kumar Sahu
- School of Chemical Sciences, National Institute of Science Education and Research , Bhubaneswar 751005, India
| | - Arindam Ghosh
- School of Chemical Sciences, National Institute of Science Education and Research , Bhubaneswar 751005, India
| | - Moloy Sarkar
- School of Chemical Sciences, National Institute of Science Education and Research , Bhubaneswar 751005, India
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