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Pontoni D, DiMichiel M, Murphy BM, Honkimäki V, Deutsch M. Ordering of ionic liquids at a charged sapphire interface: Evolution with cationic chain length. J Colloid Interface Sci 2024; 661:33-45. [PMID: 38295701 DOI: 10.1016/j.jcis.2024.01.126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 01/09/2024] [Accepted: 01/18/2024] [Indexed: 02/27/2024]
Abstract
HYPOTHESIS Room Temperature Ionic Liquids (RTILs) bulk's molecular layering dominates their structure also at the RTIL/sapphire interface, increasing the layer spacing with the cationic alkyl chain length n. However, the negatively-charged sapphire surface compresses the layers, increases the layering range, and affects the intra-layer structure in yet unknown ways. EXPERIMENTS X-ray reflectivity (XR) off the RTIL/sapphire interface, for a broad homologous RTIL series 1-alkyl-3-methylimidazolium bis(trifluoromethansulfonyl)imide, hitherto unavailable for any RTIL. FINDINGS RTIL layers against the sapphire, exhibit two spacings: da and db. da is n-varying, follows the behavior of the bulk spacing but exhibits a downshift, thus showing significant layer compression, and over twofold polar slab thinning. The latter suggests exclusion of anions from the interfacial region due to the negative sapphire charging by x-ray-released electrons. The layering range is larger than the bulk's. db is short and near n-independent, suggesting polar moieties' layering, the coexistence mode of which with the da-spaced layering is unclear. Comparing the present layering with the bulk's and the RTIL/air interface's provides insight into the Coulomb and dispersion interaction balance dominating the RTIL's structure and the impact thereon of the presence of a charged solid interface.
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Affiliation(s)
- Diego Pontoni
- ESRF - The European Synchrotron, 71 Avenue des Martyrs, 38043 Grenoble, France
| | - Marco DiMichiel
- ESRF - The European Synchrotron, 71 Avenue des Martyrs, 38043 Grenoble, France
| | - Bridget M Murphy
- Institute of Experimental and Applied Physics, Kiel University, Kiel D-24098, Germany; Ruprecht-Haensel Laboratory, Kiel University, Kiel D-24118, Germany
| | - Veijo Honkimäki
- ESRF - The European Synchrotron, 71 Avenue des Martyrs, 38043 Grenoble, France
| | - Moshe Deutsch
- Physics Dept. & Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan, Israel.
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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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3
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Babamale HF, Khor BK, Chear NJY, Haque RA, Yam W. The First tetrafluorinated azobenzene-imidazolium ionic conjugates as potential thermotropic liquid crystalline drugs: Self-assembly properties and cytotoxic effects. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.132470] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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4
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Saielli G. The effect of hydration on the stability of ionic liquid crystals: MD simulations of [C 14C 1im]Cl and [C 14C 1im]Cl·H 2O. Phys Chem Chem Phys 2021; 23:24386-24395. [PMID: 34676847 DOI: 10.1039/d1cp03757a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The thermal range of the stability of Ionic Liquid Crystal (ILC) phases of imidazolium ILCs, and the type of the mesophase itself are affected by several molecular structural features, the two prominent ones being the alkyl chain length and the counter-anion. Hydration is also very important: monohydrate samples of 1-alkyl-3-methylimidazolium halides have a higher clearing point and a wider thermal range of the stability of the ionic smectic phase, compared with the analogous anhydrous sample. To understand the reasons, at a microscopic level, for such increased stability due to hydration, we run classical Molecular Dynamics (MD) simulations of a typical ionic liquid crystal, 1-tetradecyl-3-methylimidazolium chloride, and of its monohydrate form. We tested a full-charge non-polarizable force field and a scaled-charge version having the total charge of the ions scaled by a factor of 0.80. Comparison of the structural and dynamic properties with available experimental data reveals that the scaling of the charge by a factor of 0.80 results in a good agreement between simulated and experimental data and it sheds light on the microscopic mechanism responsible for the increased stability of the monohydrated phase. A hydrogen-bond network between water and the chloride anion is established in the ionic layer which increases the stability of the ionic layer; this in turn increases the nano-segregation between the ionic and hydrophobic layers which eventually produce an increased order of the alkylic layer as well.
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Affiliation(s)
- Giacomo Saielli
- CNR Institute on Membrane Technology, Padova Section, Via Marzolo, 1-35131 Padova, Italy. .,Department of Chemical Sciences, University of Padova, Via Marzolo, 1-35131 - Padova, Italy
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5
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Wang YL, Li B, Laaksonen A. Coarse-grained simulations of ionic liquid materials: from monomeric ionic liquids to ionic liquid crystals and polymeric ionic liquids. Phys Chem Chem Phys 2021; 23:19435-19456. [PMID: 34524303 DOI: 10.1039/d1cp02662c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ionic liquid (IL) materials are promising electrolytes with striking physicochemical properties for energy and environmental applications. Heterogeneous structures and transport quantities of monomeric and polymeric ILs are intrinsically intercorrelated and span multiple spatiotemporal scales, which is more feasible for coarse-grained (CG) simulations than atomistic modelling. Herein we constructed a novel CG model for ethyl-imidazolium tetrafluoroborate ILs with varied cation alkyl chains ranging from C2 to C20, and the interaction parameters were validated against representative static and dynamic properties that were obtained from atomistic reference simulations and experimental characterizations at relevant thermodynamic states. This CG model was extended to study thermotropic phase behaviors of monomeric ILs and to explore ion association structures and ion transport quantities in polymeric ILs with different architectures. A systematic analysis of structural and dynamical quantities identifies an evolution of liquid morphology from homogeneous to nanosegregated structures and then a smectic mesomorphism via a gradual lengthening of cation alkyl chains, and thereafter a distinct structural transition characterized by a monotonic decrease in orientational and translational order parameters in a sequential heating cascade. Backbone and pendant polymeric ILs exhibit evident anion association structures with cation monomers and polymer chains, and striking intra- and interchain coordinations between cation monomers owing to an intrinsic polymer architecture effect. Such a peculiar ion pairing association leads to a progressive increase in anion intrachain hopping probabilities, and a concomitant decrease in anion interchain hopping events with a gradual lengthening of polymeric ILs. The anion diffusivities in polymeric ILs are intrinsically correlated with ion pairing association lifetimes and ion structural relaxation times via a universal power law correlation D ∼ τ-1, irrespective of polymer architectures.
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Affiliation(s)
- Yong-Lei Wang
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden.
| | - Bin Li
- School of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai 519082, P. R. China
| | - Aatto Laaksonen
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden. .,State Key Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing 210009, P. R. China.,Centre of Advanced Research in Bionanoconjugates and Biopolymers, Petru Poni Institute of Macromolecular Chemistry, Aleea Grigore Ghica-Voda, 41A, 700487 Iasi, Romania.,Department of Engineering Sciences and Mathematics, Division of Energy Science, Luleå University of Technology, SE-97187 Luleå, Sweden
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6
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Saielli G, Castiglione F, Mauri M, Simonutti R, Mele A. Xenon Diffusion in Ionic Liquids with Blurred Nanodomain Separation. Chemphyschem 2021; 22:1880-1890. [PMID: 34251740 DOI: 10.1002/cphc.202100423] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/11/2021] [Indexed: 11/09/2022]
Abstract
The dynamics of xenon gas, loaded in a series of 1-alkyl-3-methylimidazolium based ionic liquids, probes the formation of increasingly blurred polar/apolar nanodomains as a function of the anion type and the cation chain length. Exploiting 129 Xe NMR spectroscopy techniques, like Pulse Gradient Spin Echo (PGSE) and inversion recovery (IR), the diffusion motion and relaxation times are determined for 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Cn C1 im][TFSI]. A correlation between the ILs nano-structure and both xenon diffusivity and relaxation times, as well as chemical shifts, is outlined. Interestingly, comparison with previous results of the same properties in the homologous imidazolium chlorides and hexafluorophospate shows an opposite trend with the alkyl chain length. Classical molecular dynamics (MD) simulations are used to calculate the xenon and cation and anion diffusion coefficients in the same systems, including imidazolium cations with longer chains (n=4, 6, 8 … 20). An almost quantitative agreement with the experiments validates the MD simulations and, at the same time, provides the necessary structural and dynamic microscopic insights on the nano-segregation and diffusion of xenon in bistriflimide, chloride and hexafluorphosphate salts allowing to observe and rationalize the shaping effect of the cation in the nanostructure.
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Affiliation(s)
- Giacomo Saielli
- CNR - ITM Institute on Membrane Technology, Padova Unit, Via Marzolo, 1, 35131, Padova, Italy.,Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padova, Italy
| | - Franca Castiglione
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. Da Vinci, 32, 20133, Milano, Italy
| | - Michele Mauri
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Roberto Cozzi, 53, 20125, Milano, Italy
| | - Roberto Simonutti
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Roberto Cozzi, 53, 20125, Milano, Italy
| | - Andrea Mele
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. Da Vinci, 32, 20133, Milano, Italy.,CNR - SCITEC Istituto di Scienze e Tecnologie Chimiche, Via A. Corti 12, 20133, Milano, Italy
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7
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Riccobono A, Lazzara G, Rogers SE, Pibiri I, Pace A, Slattery JM, Bruce DW. Synthesis and mesomorphism of related series of triphilic ionic liquid crystals based on 1,2,4-triazolium cations. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2020.114758] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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8
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Pontoni D, DiMichiel M, Deutsch M. Nanoscale Structure in Short‐Chain Ionic Liquids. Chemphyschem 2020; 21:1887-1897. [DOI: 10.1002/cphc.202000548] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Indexed: 02/03/2023]
Affiliation(s)
- Diego Pontoni
- Partnership for Soft Condensed Matter (PSCM) ESRF – The European Synchrotron 71 Avenue des Martyrs 38043 Grenoble France
| | - Marco DiMichiel
- ESRF – The European Synchrotron 71 Avenue des Martyrs 38043 Grenoble France
| | - Moshe Deutsch
- Physics Dept. & Institute of Nanotechnology and Advanced Materials Bar-Ilan University Ramat Gan Israel
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9
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Bhowmik PK, Al-Karawi MKM, Killarney ST, Dizon EJ, Chang A, Kim J, Chen SL, Principe RCG, Ho A, Han H, Mandal HD, Cortez RG, Gutierrez B, Mendez K, Sharpnack L, Agra-Kooijman DM, Fisch MR, Kumar S. Thermotropic Liquid-Crystalline and Light-Emitting Properties of Bis(4-aalkoxyphenyl) Viologen Bis(triflimide) Salts. Molecules 2020; 25:E2435. [PMID: 32456122 PMCID: PMC7288076 DOI: 10.3390/molecules25102435] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 05/21/2020] [Accepted: 05/21/2020] [Indexed: 11/21/2022] Open
Abstract
A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1H and 13C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, Tms, and SmA-to-isotropic transitions, Tis. Those with longer length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330-370 °C. Their light-emitting properties in methanol were also included.
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Affiliation(s)
- Pradip K. Bhowmik
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Muhammed Kareem M. Al-Karawi
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Shane T. Killarney
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Erenz J. Dizon
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Anthony Chang
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Jongin Kim
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Si L. Chen
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Ronald Carlo G. Principe
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Andy Ho
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Haesook Han
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA; (M.K.M.A.-K.); (S.T.K.); (E.J.D.); (A.C.); (J.K.); (S.L.C.); (R.C.G.P.); (A.H.); (H.H.)
| | - Hari D. Mandal
- Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA; (H.D.M.); (R.G.C.); (B.G.); (K.M.)
| | - Raymond G. Cortez
- Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA; (H.D.M.); (R.G.C.); (B.G.); (K.M.)
| | - Bryan Gutierrez
- Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA; (H.D.M.); (R.G.C.); (B.G.); (K.M.)
| | - Klarissa Mendez
- Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA; (H.D.M.); (R.G.C.); (B.G.); (K.M.)
| | - Lewis Sharpnack
- Department of Earth Science, 1006 Webb Hall, University of California, Santa Barbara, CA 93106, USA;
| | - Deña M. Agra-Kooijman
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA;
| | - Michael R. Fisch
- College of Aeronautics and Engineering, Kent State University, Kent, OH 44242, USA;
| | - Satyendra Kumar
- Division of Research, University at Albany, Albany, NY 12222, USA;
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Pontoni D, DiMichiel M, Deutsch M. Temperature evolution of the bulk nano-structure in a homologous series of room temperature ionic liquids. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2019.112280] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Haddad J, Pontoni D, Murphy BM, Festersen S, Runge B, Magnussen OM, Steinrück HG, Reichert H, Ocko BM, Deutsch M. Surface structure evolution in a homologous series of ionic liquids. Proc Natl Acad Sci U S A 2018; 115:E1100-E1107. [PMID: 29358372 PMCID: PMC5819424 DOI: 10.1073/pnas.1716418115] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Interfaces of room temperature ionic liquids (RTILs) are important for both applications and basic science and are therefore intensely studied. However, the evolution of their interface structure with the cation's alkyl chain length [Formula: see text] from Coulomb to van der Waals interaction domination has not yet been studied for even a single broad homologous RTIL series. We present here such a study of the liquid-air interface for [Formula: see text], using angstrom-resolution X-ray methods. For [Formula: see text], a typical "simple liquid" monotonic surface-normal electron density profile [Formula: see text] is obtained, like those of water and organic solvents. For [Formula: see text], increasingly more pronounced nanoscale self-segregation of the molecules' charged moieties and apolar chains yields surface layering with alternating regions of headgroups and chains. The layering decays into the bulk over a few, to a few tens, of nanometers. The layering periods and decay lengths, their linear [Formula: see text] dependence, and slopes are discussed within two models, one with partial-chain interdigitation and the other with liquid-like chains. No surface-parallel long-range order is found within the surface layer. For [Formula: see text], a different surface phase is observed above melting. Our results also impact general liquid-phase issues like supramolecular self-aggregation and bulk-surface structure relations.
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Affiliation(s)
- Julia Haddad
- Physics Department, Bar-Ilan University, Ramat Gan 5290002, Israel
- Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 5290002, Israel
| | - Diego Pontoni
- European Synchrotron Radiation Facility, The European Synchrotron and Partnership for Soft Condensed Matter (PSCM), 38000 Grenoble, France
| | - Bridget M Murphy
- Institute for Experimental and Applied Physics, Kiel University, 24118 Kiel, Germany
- Ruprecht Haensel Laboratory, Kiel University, 24098 Kiel, Germany
| | - Sven Festersen
- Institute for Experimental and Applied Physics, Kiel University, 24118 Kiel, Germany
| | - Benjamin Runge
- Institute for Experimental and Applied Physics, Kiel University, 24118 Kiel, Germany
| | - Olaf M Magnussen
- Institute for Experimental and Applied Physics, Kiel University, 24118 Kiel, Germany
- Ruprecht Haensel Laboratory, Kiel University, 24098 Kiel, Germany
| | - Hans-Georg Steinrück
- Stanford Synchrotron Radiation Laboratory (SSRL) Materials Science Division, Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory, Menlo Park, CA 94025
| | - Harald Reichert
- European Synchrotron Radiation Facility, The European Synchrotron, 38000 Grenoble, France
| | - Benjamin M Ocko
- National Synchrotron Light Source II (NSLS-II), Brookhaven National Laboratory, Upton, NY 11973
| | - Moshe Deutsch
- Physics Department, Bar-Ilan University, Ramat Gan 5290002, Israel;
- Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 5290002, Israel
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Mars J, Hou B, Weiss H, Li H, Konovalov O, Festersen S, Murphy BM, Rütt U, Bier M, Mezger M. Surface induced smectic order in ionic liquids - an X-ray reflectivity study of [C 22C 1im] +[NTf 2] . Phys Chem Chem Phys 2018; 19:26651-26661. [PMID: 28960006 DOI: 10.1039/c7cp04852a] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Surface induced smectic order was found for the ionic liquid 1-methyl-3-docosylimidazolium bis(trifluoromethlysulfonyl)imide by X-ray reflectivity and grazing incidence scattering experiments. Near the free liquid surface, an ordered structure of alternating layers composed of polar and non-polar moieties is observed. This leads to an oscillatory interfacial profile perpendicular to the liquid surface with a periodicity of 3.7 nm. Small angle X-ray scattering and polarized light microscopy measurements suggest that the observed surface structure is related to fluctuations into a metastable liquid crystalline SmA2 phase that was found by supercooling the bulk liquid. The observed surface ordering persists up to 157 °C, i.e. more than 88 K above the bulk melting temperature of 68.1 °C. Close to the bulk melting point, we find a thickness of the ordered layer of L = 30 nm. The dependency of L(τ) = Λ ln(τ/τ1) vs. reduced temperature τ follows a logarithmic growth law. In agreement with theory, the pre-factor Λ is governed by the correlation length of the isotropic bulk phase.
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Affiliation(s)
- Julian Mars
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
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Pontoni D, Haddad J, Di Michiel M, Deutsch M. Self-segregated nanostructure in room temperature ionic liquids. SOFT MATTER 2017; 13:6947-6955. [PMID: 28849840 DOI: 10.1039/c7sm01464c] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The nanosegregated bulk structure, and its evolution with the cation's alkyl length n, are studied by X-ray scattering for an unprecedentedly broad homologous series of a model room-temperature ionic liquid, [CnMIM][NTf2] (n = 4-22). A tri-periodic local structure is found, with the lateral periodicities, dII and dIII independent of n, and a longitudinal one, dI, linearly increasing with n. The results are consistent with a local structure comprising alternating layers of polar headgroups and apolar, interdigitated, partly overlapping, cations' alkyl tails, of an average macroscopic mass density close to that of liquid alkanes. A slope decrease in the linear dI(n) suggests a change from a lower to a higher rate of increase with n of chain overlap for n ≥ 12. The order decay lengths of the layering, and of the lateral chain packing, increase with n, as expected from the increasing van der Waals interaction's domination of the structure. The headgroups' lateral packing decay length decreases with n, due to increasing frustration between the longer lateral periodicity preferred by the headgroups, and the shorter lateral periodicity preferred by the chains. A comparison of the bulk and surface structures highlights the surface's ordering effect, which, however, does not induce here a surface phase different from the bulk, as it does in liquid crystals and liquid alkanes.
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Affiliation(s)
- Diego Pontoni
- ESRF - The European Synchrotron and Partnership for Soft Condensed Matter (PSCM), 71 Avenue des Martyrs, 38000 Grenoble, France
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Weiss H, Mars J, Li H, Kircher G, Ivanova O, Feoktystov A, Soltwedel O, Bier M, Mezger M. Mesoscopic Correlation Functions in Heterogeneous Ionic Liquids. J Phys Chem B 2017; 121:620-629. [PMID: 28001074 DOI: 10.1021/acs.jpcb.6b11220] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A common feature of ionic liquids composed of cations with long aliphatic side chains is structural heterogeneities on the nanometer length scale. This so-called microphase separation arises from the clustering of aliphatic moieties. The temperature dependence of the liquid bulk structure was studied by small-angle X-ray and neutron scattering for a set of methylimidazolium ([C18C1im]+, [C22C1im]+) based ionic liquids with tris(pentafluoroethyl)trifluorophosphate ([FAP]-), bis(trifluoromethylsulfonyl)imide ([NTf2]-), and bis(nonafluorobutylsulfonyl)imide ([NNf2]-) anions. The experimental data is quantitatively analyzed using a generalized Teubner-Strey model. Discussion of the resulting periodicity d and correlation length ξ shows that the structural heterogeneities are governed by the interplay between the alkyl chain length, the geometry of the anion, and entropic effects. Connections between the mesoscopic correlation functions, density, and entropy of fusion are discussed in comparison to alcohols. The observed dependencies allow predictions on the mesoscopic correlation functions based on macroscopic bulk quantities.
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Affiliation(s)
- Henning Weiss
- Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany
| | - Julian Mars
- Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.,Institute of Physics, Johannes Gutenberg University Mainz , 55128 Mainz, Germany
| | - Hailong Li
- Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany
| | - Gunnar Kircher
- Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany
| | - Oxana Ivanova
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH , Lichtenbergstr. 1, 85748 Garching, Germany
| | - Artem Feoktystov
- Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH , Lichtenbergstr. 1, 85748 Garching, Germany
| | - Olaf Soltwedel
- Max Planck Institute for Solid State Research , Outstation at Heinz Maier-Leibnitz Zentrum, Lichtenbergstr. 1, 85747 Garching, Germany
| | - Markus Bier
- Max Planck Institute for Intelligent Systems , Heisenbergstr. 3, 70569 Stuttgart, Germany.,Institute for Theoretical Physics IV, University of Stuttgart , Pfaffenwaldring 57, 70569 Stuttgart, Germany
| | - Markus Mezger
- Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.,Institute of Physics, Johannes Gutenberg University Mainz , 55128 Mainz, Germany
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15
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Nelyubina YV, Shaplov AS, Lozinskaya EI, Buzin MI, Vygodskii YS. A New Volume-Based Approach for Predicting Thermophysical Behavior of Ionic Liquids and Ionic Liquid Crystals. J Am Chem Soc 2016; 138:10076-9. [PMID: 27479022 DOI: 10.1021/jacs.6b05174] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Volume-based prediction of melting points and other properties of ionic liquids (ILs) relies on empirical relations with volumes of ions in these low-melting organic salts. Here we report an accurate way to ionic volumes by Bader's partitioning of electron densities from X-ray diffraction obtained via a simple database approach. For a series of 1-tetradecyl-3-methylimidazolium salts, the volumes of different anions are found to correlate linearly with melting points; larger anions giving lower-melting ILs. The volume-based concept is transferred to ionic liquid crystals (ILs that adopt liquid crystalline mesophases, ILCs) for predicting the domain of their existence from the knowledge of their constituents. For 1-alkyl-3-methylimidazolium ILCs, linear correlations of ionic volumes with the occurrence of LC mesophase and its stability are revealed, thus paving the way to rational design of ILCs by combining suitably sized ions.
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Affiliation(s)
- Yulia V Nelyubina
- A. N. Nesmeyanov Institute of Organoelement Compounds , Vavilova Str., 28, Moscow 119991, Russia
| | - Alexander S Shaplov
- A. N. Nesmeyanov Institute of Organoelement Compounds , Vavilova Str., 28, Moscow 119991, Russia
| | - Elena I Lozinskaya
- A. N. Nesmeyanov Institute of Organoelement Compounds , Vavilova Str., 28, Moscow 119991, Russia
| | - Mikhail I Buzin
- A. N. Nesmeyanov Institute of Organoelement Compounds , Vavilova Str., 28, Moscow 119991, Russia
| | - Yakov S Vygodskii
- A. N. Nesmeyanov Institute of Organoelement Compounds , Vavilova Str., 28, Moscow 119991, Russia
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16
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Goossens K, Lava K, Bielawski CW, Binnemans K. Ionic Liquid Crystals: Versatile Materials. Chem Rev 2016; 116:4643-807. [PMID: 27088310 DOI: 10.1021/cr400334b] [Citation(s) in RCA: 411] [Impact Index Per Article: 51.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.
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Affiliation(s)
- Karel Goossens
- Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS) , Ulsan 689-798, Republic of Korea.,Department of Chemistry, KU Leuven , Celestijnenlaan 200F, P.O. Box 2404, B-3001 Heverlee, Belgium
| | - Kathleen Lava
- Department of Chemistry, KU Leuven , Celestijnenlaan 200F, P.O. Box 2404, B-3001 Heverlee, Belgium.,Department of Organic and Macromolecular Chemistry, Ghent University , Krijgslaan 281 S4, B-9000 Ghent, Belgium
| | - Christopher W Bielawski
- Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS) , Ulsan 689-798, Republic of Korea.,Department of Chemistry and Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST) , Ulsan 689-798, Republic of Korea
| | - Koen Binnemans
- Department of Chemistry, KU Leuven , Celestijnenlaan 200F, P.O. Box 2404, B-3001 Heverlee, Belgium
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