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Elstone NS, Shaw EV, Shimizu K, Lai J, Demé B, Lane PD, Costen ML, McKendrick KG, Youngs S, Rogers SE, Canongia Lopes JN, Bruce DW, Slattery JM. Chain-length dependent organisation in mixtures of hydrogenous and fluorous ionic liquids. Faraday Discuss 2024. [PMID: 39091139 DOI: 10.1039/d4fd00047a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/04/2024]
Abstract
As part of an ongoing study of the structure and properties of mixtures of ionic liquids in which one component has a hydrocarbon chain and the other a semiperfluorocarbon chain, we now report a study of the mixtures [C8MIM]1-x[C10MIM-F17]x[Tf2N], [C10MIM]1-x[C8MIM-F13]x[Tf2N] and [C10MIM]1-x[C10MIM-F17]x[Tf2N], where [C8MIM][Tf2N] is 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide, [C10MIM][Tf2N] is 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C8MIM-F13][Tf2N] is 1-(1H,1H,2H,2H-perfluorooctyl)-3-methylimidizolium bis(trifluoromethylsulfonyl)imide and [C10MIM-F17][Tf2N] is 1-(1H,1H,2H,2H-perfluorodecyl)-3-methylimidizolium bis(trifluoromethylsulfonyl)imide. The mixtures were investigated using small-angle X-ray (SAXS) and neutron (SANS) scattering complemented by molecular dynamics simulations (with viscosity and surface tension measurements also possible for the mixtures [C10MIM]1-x[C8MIM-F13]x[Tf2N]). Unlike previous studies of [C8MIM]1-x[C8MIM-F13]x[Tf2N], where no strong evidence of alkyl/fluoroalkyl chain segregation or triphilic behaviour was seen (Elstone et al., J. Phys. Chem. B, 2023, 127, 7394-7407), these new mixtures show the formation of small aggregates of varying sizes of each component, even though all were co-miscible across the full range of compositions. Thus, while a clear polar non-polar peak (PNPP) was observed at large or small values of x, at intermediate compositions the small-angle neutron scattering at low q was dominated by scattering from these small aggregates, while at other compositions, there was little or no evidence of the PNPP. The origins of this behaviour are discussed in terms of inter-chain interactions.
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Affiliation(s)
- Naomi S Elstone
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - Emily V Shaw
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - Karina Shimizu
- Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1049 001, Portugal.
| | - Joshua Lai
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - Bruno Demé
- Institut Laue-Langevin, Grenoble 38000, France
| | - Paul D Lane
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Matthew L Costen
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Kenneth G McKendrick
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Sarah Youngs
- ISIS Neutron and Muon Source, Harwell Campus, Didcot OX11 0QX, UK
| | - Sarah E Rogers
- ISIS Neutron and Muon Source, Harwell Campus, Didcot OX11 0QX, UK
| | - Jose N Canongia Lopes
- Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa 1049 001, Portugal.
| | - Duncan W Bruce
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - John M Slattery
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
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Pontoni D, DiMichiel M, Deutsch M. Binary mixtures of homologous room-temperature ionic liquids: Nanoscale structure evolution with alkyl lengths’ difference. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.118874] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Oz E, Sahin O, Okur HI, Suzer S. Surface Propensity of Anions in a Binary Ionic-Liquid Mixture Assessed by Full-Range Angle-Resolved X-ray Photoelectron Spectroscopy and Surface-Tension Measurements. Chemphyschem 2020; 21:2397-2401. [PMID: 32955763 DOI: 10.1002/cphc.202000750] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/18/2020] [Indexed: 11/09/2022]
Abstract
Angle-resolved X-ray photoelectron spectroscopy and contact-angle measurements guided by a signal attenuation model are utilized to extract molar composition and anion enrichment in the vacuum interface of a binary ionic liquid mixture, having a common quaternary ammonium cation and two different anions. By using the intensity ratio of the F1s peaks belonging to the two different anions recorded at the full electron take-off angle range, from 0° to 80°, we have determined that only a fractionally covered and anion enriched surface layer can predict the AR-XPS data, which is also consistent with surface tension measurements. Moreover, the more bulky and non-spherical anion enrichment is evident even at the conventional and the so assumed bulk sensitive take-off angle of 0°. This methodology provides a surface enrichment factor of the molecular ions and clearly serves as an experimental evidence for recently debated surface layering and/or island structure in ionic liquid systems.
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Affiliation(s)
- Erdinc Oz
- Department of Chemistry, Bilkent University, 06800, Ankara, Turkey
| | - Ozgur Sahin
- Department of Chemistry, Bilkent University, 06800, Ankara, Turkey
| | - Halil I Okur
- Department of Chemistry, Bilkent University, 06800, Ankara, Turkey
| | - Sefik Suzer
- Department of Chemistry, Bilkent University, 06800, Ankara, Turkey
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Heller BS, Paap U, Maier F, Steinrück HP. Pronounced surface enrichment of fluorinated ionic liquids in binary mixtures with methoxy-functionalized ionic liquids. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.112783] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Heller BSJ, Lexow M, Greco F, Shin S, Partl G, Maier F, Steinrück HP. Temperature-Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non-Fluorinated Ionic Liquids. Chemistry 2020; 26:1117-1126. [PMID: 31633251 PMCID: PMC7027538 DOI: 10.1002/chem.201904438] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Indexed: 11/05/2022]
Abstract
Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at different temperatures in the liquid state. The mixtures consist of ILs with the same [PF6 ]- anion but two different cations, namely 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF6 ], and 1-butyl-3-methylimidazolium hexafluorophosphate, [C4 C1 Im][PF6 ], with 10, 25, 50 and 75 mol % content of [PFBMIm][PF6 ]. We observe a preferential enrichment of the fluorinated chain in the topmost layer, relative to the bulk composition, which is most pronounced for the lowest content of [PFBMIm][PF6 ]. Upon cooling the mixtures stepwise from 95 °C until surface charging effects in XPS indicate solidification, we observe a pronounced increase in surface enrichment of the fluorinated chain with decreasing temperature in the liquid state. In contrast to the mixtures with lower [PFBMIm][PF6 ] contents, cooling the 75 mol % mixture additionally shows an abrupt decrease of the fluorinated chain signal before complete solidification occurs, which is assigned to partial precipitation effects.
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Affiliation(s)
- Bettina S J Heller
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Matthias Lexow
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Francesco Greco
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Sunghwan Shin
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Gabriel Partl
- Institut für Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens-Universität Innsbruck, Innrain 80-82, 6020, Innsbruck, Austria
| | - Florian Maier
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Hans-Peter Steinrück
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
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Heller BSJ, Kolbeck C, Niedermaier I, Dommer S, Schatz J, Hunt P, Maier F, Steinrück HP. Surface Enrichment in Equimolar Mixtures of Non-Functionalized and Functionalized Imidazolium-Based Ionic Liquids. Chemphyschem 2018; 19:1733-1745. [PMID: 29645340 PMCID: PMC6175172 DOI: 10.1002/cphc.201800216] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Indexed: 11/30/2022]
Abstract
For equimolar mixtures of ionic liquids with imidazolium‐based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle‐resolved X‐ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1‐methyl‐3‐octylimidazolium hexafluorophosphate+1,3‐di(methoxy)imidazolium hexafluorophosphate ([C8C1Im][PF6]+[(MeO)2Im][PF6]), we find a strong enrichment of the octyl chain‐containing [C8C1Im]+ cation and a corresponding depletion of the [(MeO)2Im]+ cation in the topmost layer. For a mixture with different cations and anions, that is, [C8C1Im][Tf2N]+[(MeO)2Im][PF6], we find both surface enrichment of the [C8C1Im]+ cation and the [Tf2N]− (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO)2Im]+ and [PF6]− are depleted from the surface. We propose that the observed behavior in these mixtures is due to a lowering of the surface tension by the enriched components. Interestingly, we observe pronounced differences in the chemical shifts of the imidazolium ring signals of the [(MeO)2Im]+ cations as compared to the non‐functionalized cations. Calculations of the electronic structure and the intramolecular partial charge distribution of the cations contribute to interpreting these shifts for the two different cations.
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Affiliation(s)
- Bettina S J Heller
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Claudia Kolbeck
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Inga Niedermaier
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Sabine Dommer
- Lehrstuhl für Organische Chemie I, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nikolaus-Fiebiger-Straße 10, 91058, Erlangen, Germany
| | - Jürgen Schatz
- Lehrstuhl für Organische Chemie I, Friedrich-Alexander-Universität Erlangen-Nürnberg, Nikolaus-Fiebiger-Straße 10, 91058, Erlangen, Germany
| | - Patricia Hunt
- Chemistry Department, Imperial College London, SW72AZ, London, United Kingdom
| | - Florian Maier
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
| | - Hans-Peter Steinrück
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany
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Smoll EJ, Tesa-Serrate MA, Purcell SM, D'Andrea L, Bruce DW, Slattery JM, Costen ML, Minton TK, McKendrick KG. Determining the composition of the vacuum-liquid interface in ionic-liquid mixtures. Faraday Discuss 2018; 206:497-522. [PMID: 28944811 DOI: 10.1039/c7fd00175d] [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
The vacuum-liquid interfaces of a number of ionic-liquid mixtures have been investigated using the combination of reactive-atom scattering with laser-induced fluorescence detection (RAS-LIF), selected surface tension measurements, and molecular dynamics (MD) simulations. The mixtures are based on the widespread 1-alkyl-3-methylimidazolium ([Cnmim]+) cation, including mixed cations which differ in chain length or chemical functionality with a common anion; and different anions for a common cation. RAS-LIF results imply that the surface compositions exhibit a general form of non-stoichiometric behaviour that mimics the well-known Henry's and Raoult's laws at low and high mole fraction, respectively. The extended Langmuir model provides a moderately good single-parameter fit, but higher-order terms are required for an accurate description. The quantitative relationship between RAS-LIF and surface tension, which probes the surface composition only indirectly, is explored for mixtures of [C2mim]+ and [C12mim]+ with a common bis(trifluoromethylsulfonyl)imide ([NTf2]-) anion. Extended Langmuir model fits to surface tension data are broadly consistent with those to RAS-LIF; however, several other common approaches to extracting surface compositions from measured surface tensions result in much larger discrepancies. MD simulations suggest that RAS-LIF faithfully reports on the alkyl-chain exposure at the surface, which is only subtly modified by composition-dependent structural reorganisation.
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Affiliation(s)
- E J Smoll
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, USA.
| | - M A Tesa-Serrate
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - S M Purcell
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - L D'Andrea
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
| | - D W Bruce
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
| | - J M Slattery
- Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
| | - M L Costen
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - T K Minton
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, USA.
| | - K G McKendrick
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
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Bruce DW, Cabry CP, Lopes JNC, Costen ML, D'Andrea L, Grillo I, Marshall BC, McKendrick KG, Minton TK, Purcell SM, Rogers S, Slattery JM, Shimizu K, Smoll E, Tesa-Serrate MA. Nanosegregation and Structuring in the Bulk and at the Surface of Ionic-Liquid Mixtures. J Phys Chem B 2017; 121:6002-6020. [PMID: 28459567 DOI: 10.1021/acs.jpcb.7b01654] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ionic-liquid (IL) mixtures hold great promise, as they allow liquids with a wide range of properties to be formed by mixing two common components rather than by synthesizing a large array of pure ILs with different chemical structures. In addition, these mixtures can exhibit a range of properties and structural organization that depend on their composition, which opens up new possibilities for the composition-dependent control of IL properties for particular applications. However, the fundamental properties, structure, and dynamics of IL mixtures are currently poorly understood, which limits their more widespread application. This article presents the first comprehensive investigation into the bulk and surface properties of IL mixtures formed from two commonly encountered ILs: 1-ethyl-3-methylimidazolium and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][Tf2N] and [C12mim][Tf2N]). Physical property measurements (viscosity, conductivity, and density) reveal that these IL mixtures are not well described by simple mixing laws, implying that their structure and dynamics are strongly composition dependent. Small-angle X-ray and neutron scattering measurements, alongside molecular dynamics (MD) simulations, show that at low mole fractions of [C12mim][Tf2N], the bulk of the IL is composed of small aggregates of [C12mim]+ ions in a [C2mim][Tf2N] matrix, which is driven by nanosegregation of the long alkyl chains and the polar parts of the IL. As the proportion of [C12mim][Tf2N] in the mixtures increases, the size and number of aggregates increases until the C12 alkyl chains percolate through the system and a bicontinuous network of polar and nonpolar domains is formed. Reactive atom scattering-laser-induced fluorescence experiments, also supported by MD simulations, have been used to probe the surface structure of these mixtures. It is found that the vacuum-IL interface is enriched significantly in C12 alkyl chains, even in mixtures low in the long-chain component. These data show, in contrast to previous suggestions, that the [C12mim]+ ion is surface active in this binary IL mixture. However, the surface does not become saturated in C12 chains as its proportion in the mixtures increases and remains unsaturated in pure [C12mim][Tf2N].
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Affiliation(s)
- Duncan W Bruce
- Department of Chemistry, University of York , Heslington, York YO10 5DD, U.K
| | - Christopher P Cabry
- Department of Chemistry, University of York , Heslington, York YO10 5DD, U.K
| | - José N Canongia Lopes
- Centro de Química Estrutural, IST, Universidade de Lisboa , 1049-001 Lisboa, Portugal.,ITQB, Universidade Nova de Lisboa , Avenida República, 2780-157 Oeiras, Portugal
| | - Matthew L Costen
- Institute of Chemical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, U.K
| | - Lucía D'Andrea
- Department of Chemistry, University of York , Heslington, York YO10 5DD, U.K
| | - Isabelle Grillo
- ILL , 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
| | - Brooks C Marshall
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Kenneth G McKendrick
- Institute of Chemical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, U.K
| | - Timothy K Minton
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Simon M Purcell
- Institute of Chemical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, U.K
| | - Sarah Rogers
- ISIS, Science & Technology Facilities Council, Rutherford Appleton Laboratory , OX11 0QX Chilton, U.K
| | - John M Slattery
- Department of Chemistry, University of York , Heslington, York YO10 5DD, U.K
| | - Karina Shimizu
- Centro de Química Estrutural, IST, Universidade de Lisboa , 1049-001 Lisboa, Portugal.,ITQB, Universidade Nova de Lisboa , Avenida República, 2780-157 Oeiras, Portugal
| | - Eric Smoll
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - María A Tesa-Serrate
- Institute of Chemical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, U.K
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Nakajima K, Nakanishi S, Chval Z, Lísal M, Kimura K. Surface segregation in a binary mixture of ionic liquids: Comparison between high-resolution RBS measurements and moleculardynamics simulations. J Chem Phys 2016; 145:184704. [PMID: 27846689 DOI: 10.1063/1.4967260] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Kaoru Nakajima
- Department of Micro Engineering, Kyoto University, Kyoto-daigaku-katsura, Nishikyo, Kyoto 615-8540, Japan
| | - Shunto Nakanishi
- Department of Micro Engineering, Kyoto University, Kyoto-daigaku-katsura, Nishikyo, Kyoto 615-8540, Japan
| | - Zdeněk Chval
- Faculty of Health and Social Studies, University of South Bohemia, České Budějovice, Czech Republic
| | - Martin Lísal
- Laboratory of Aerosols Chemistry and Physics, Institute of Chemical Process Fundamentals of the CAS, v. v. i., 165 02 Prague 6-Suchdol, Czech Republic
| | - Kenji Kimura
- Department of Micro Engineering, Kyoto University, Kyoto-daigaku-katsura, Nishikyo, Kyoto 615-8540, Japan
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Nakajima K, Zolboo E, Ohashi T, Lísal M, Kimura K. Perfect Composition Depth Profiling of Ionic Liquid Surfaces Using High-resolution RBS/ERDA. ANAL SCI 2016; 32:1089-1094. [PMID: 27725609 DOI: 10.2116/analsci.32.1089] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In order to reveal the surface structures of large molecular ionic liquids (ILs), the near-surface elemental depth distributions of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CnC1Im][Tf2N], n = 2, 6, 10) were studied using high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with high-resolution elastic recoil detection analysis (HR-ERDA). The elemental depth profiles of all constituent elements, including hydrogen, were derived from HR-ERDA/HRBS measurements, so that the profiles would reproduce both HR-ERDA and HRBS spectra simultaneously. The derived elemental depth profiles agree with state-of-the-art molecular dynamics simulations, indicating the feasibility of this method. A controversy concerning the preferential orientation of [C2C1Im] at the surface has been resolved by this new combination analysis; namely, the [C2C1Im] cation has a preferential orientation with the ethyl chain pointing towards the vacuum in the topmost molecular layer.
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Purcell SM, Tesa-Serrate MA, Marshall BC, Bruce DW, D'Andrea L, Costen ML, Slattery JM, Smoll EJ, Minton TK, McKendrick KG. Reactive-Atom Scattering from Liquid Crystals at the Liquid-Vacuum Interface: [C 12mim][BF 4] and 4-Cyano-4'-Octylbiphenyl (8CB). LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:9938-9949. [PMID: 27603521 DOI: 10.1021/acs.langmuir.6b02440] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Two complementary approaches were used to study the liquid-vacuum interface of the liquid-crystalline ionic liquid 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12mim][BF4]) in the smectic A (SmA) and isotropic phases. O atoms with two distinct incident translational energies were scattered from the surface of [C12mim][BF4]. Angle-dependent time-of-flight distributions and OH yields, respectively, were recorded from high- and low-energy O atoms. There were no significant changes in the measurements using either approach, nor the properties derived from them, accompanying the transition from the SmA to the isotropic phase. This indicates that the surface structure of [C12mim][BF4] remains essentially unchanged across the phase boundary, implying that the bulk order and surface structure are not strongly correlated for this material. This effect is ascribed to the strong propensity for the outer surfaces of ionic liquids to be dominated by alkyl chains, over an underlying layer rich in anions and cation head groups, whether or not the bulk material is a liquid crystal. In a comparative study, the OH yield from the surface of the liquid crystal, 8CB, was found to be affected by the bulk order, showing a surprising step increase at the SmA-nematic transition temperature, whose origin is the subject of speculation.
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Affiliation(s)
- Simon M Purcell
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
| | - Maria A Tesa-Serrate
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
| | - Brooks C Marshall
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Duncan W Bruce
- Department of Chemistry, University of York , Heslington, York YO10 5DD, United Kingdom
| | - Lucía D'Andrea
- Department of Chemistry, University of York , Heslington, York YO10 5DD, United Kingdom
| | - Matthew L Costen
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
| | - John M Slattery
- Department of Chemistry, University of York , Heslington, York YO10 5DD, United Kingdom
| | - Eric J Smoll
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Timothy K Minton
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Kenneth G McKendrick
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
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Blundell RK, Delorme AE, Smith EF, Licence P. An ARXPS and ERXPS study of quaternary ammonium and phosphonium ionic liquids: utilising a high energy Ag Lα′ X-ray source. Phys Chem Chem Phys 2016; 18:6122-31. [DOI: 10.1039/c5cp07089a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
A series of ammonium- and phosphonium-based ionic liquids have been probed using X-ray photoelectron spectroscopy (XPS) with a high energy Ag Lα′ X-ray source.
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Affiliation(s)
- Rebecca K. Blundell
- The GlaxoSmithKline Carbon Neutral Laboratory
- School of Chemistry
- The University of Nottingham
- Nottingham NG7 2RD
- UK
| | - Astrid E. Delorme
- The GlaxoSmithKline Carbon Neutral Laboratory
- School of Chemistry
- The University of Nottingham
- Nottingham NG7 2RD
- UK
| | - Emily F. Smith
- The GlaxoSmithKline Carbon Neutral Laboratory
- School of Chemistry
- The University of Nottingham
- Nottingham NG7 2RD
- UK
| | - Peter Licence
- The GlaxoSmithKline Carbon Neutral Laboratory
- School of Chemistry
- The University of Nottingham
- Nottingham NG7 2RD
- UK
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Hjalmarsson N, Wallinder D, Glavatskih S, Atkin R, Aastrup T, Rutland MW. Weighing the surface charge of an ionic liquid. NANOSCALE 2015; 7:16039-16045. [PMID: 26370450 DOI: 10.1039/c5nr03965g] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Electrochemical quartz crystal microbalance has been used to measure changes in the composition of the capacitive electrical double layer for 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, an ionic liquid, in contact with a gold electrode surface as a function of potential. The mass difference between the cation and anion means that the technique can effectively "weigh" the surface charge accurately with high temporal resolution. This reveals quantitatively how changing the potential alters the ratio of cations and anions associated with the electrode surface, and thus the charge per unit area, as well as the kinetics associated with these interfacial processes. The measurements reveal that it is diffusion of co-ions into the interfacial region rather than expulsion of counterions that controls the relaxation. The measured potential dependent double layer capacitance experimentally validates recent theoretical predictions for counterion overscreening (low potentials) and crowding (high potentials) at electrode surfaces. This new capacity to quantitatively measure ion composition is critical for ionic liquid applications ranging from batteries, capacitors and electrodeposition through to boundary layer structure in tribology, and more broadly provides new insight into interfacial processes in concentrated electrolyte solutions.
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Affiliation(s)
- Nicklas Hjalmarsson
- Surface and Corrosion Science, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
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