1
|
Emerson MS, Ogbodo R, Margulis CJ. Spiers Memorial Lecture: From cold to hot, the structure and structural dynamics of dense ionic fluids. Faraday Discuss 2024. [PMID: 39045616 DOI: 10.1039/d4fd00086b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2024]
Abstract
The structure of ionic liquids (ILs), which a decade or two ago was the subject of polite but heated debate, is now much better understood. This has opened opportunities to ask more sophisticated questions about the role of structure in transport, the structure of systems with ions that are not prototypical, and the similarity between ILs and other dense ionic fluids such as the high-temperature inorganic molten salts; let alone the fact that new areas of research have emerged that sprung from our collective understanding of the structure of ILs such as the deep eutectic solvents, the polymerized ionic liquids, and the zwitterionic liquids. Yet, our understanding of the structure of prototypical ILs may not be as complete as we think it to be, given that recent experiments appear to show that in some cases there may be more than one liquid phase resulting in liquid-liquid (L-L) phase transitions. This article presents a perspective on what we think are key topics related to the structure and structural dynamics of ILs and to some extent high-temperature molten salts.
Collapse
Affiliation(s)
- Matthew S Emerson
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
| | - Raphael Ogbodo
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
| | - Claudio J Margulis
- Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
| |
Collapse
|
2
|
Gao Y, Wu J, Feng Y, Han J, Fang H. Structural effects of water clusters on viscosity at high shear rates. J Chem Phys 2024; 160:104502. [PMID: 38456533 DOI: 10.1063/5.0187906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Accepted: 02/19/2024] [Indexed: 03/09/2024] Open
Abstract
In this study, we use molecular dynamics simulations of liquid water to investigate how shear thinning affects the viscosity of liquid water by structural changes of the hydrogen bond network. The effect of shear on viscosity can be divided into two parts: shear-induced destruction of the hydrogen bond network and the influence of the water structure on shear viscosity. First, strong shear destroys tetrahedral structures and thus reduces the connectivity of the hydrogen bond network. It is mainly because shear deformation, characterized by compression and expansion axes, respectively, triggers the destruction and formation of hydrogen bonds, resulting in anisotropic effects on water structures. At the same time, shear destroys large clusters and enhances the formation of small ones, resulting in a decrease in average cluster sizes. Second, the change of viscosity obeys a power law relationship with the change of hydrogen bond structures, highlighting a one-to-one correspondence between structure and property. Meanwhile, in order to explain why the structure affects viscosity, we define hydrogen-bond viscosity and find that the cooperative motion of the water structures can promote momentum transfer in the form of aggregations. Hydrogen-bond viscosity accounts for 5%-50% of the total viscosity. Our results elucidate that water structures are the important structural units to explain the change of water properties.
Collapse
Affiliation(s)
- Yitian Gao
- State Key Laboratory of Hydro-science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China
| | - Jian Wu
- Department of Physics, Tsinghua University, Beijing 100084, China
| | - Yixuan Feng
- State Key Laboratory of Hydro-science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China
| | - Jiale Han
- State Key Laboratory of Hydro-science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China
| | - Hongwei Fang
- State Key Laboratory of Hydro-science and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China
| |
Collapse
|
3
|
Palumbo O, Paolone A, Philippi F, Rauber D, Welton T. Dynamics in Quaternary Ionic Liquids with Non-Flexible Anions: Insights from Mechanical Spectroscopy. Int J Mol Sci 2023; 24:11046. [PMID: 37446222 DOI: 10.3390/ijms241311046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 06/28/2023] [Accepted: 06/29/2023] [Indexed: 07/15/2023] Open
Abstract
The present work investigates how mechanical properties and ion dynamics in ionic liquids (ILs) can be affected by ILs' design while considering possible relationships between different mechanical and transport properties. Specifically, we study mechanical properties of quaternary ionic liquids with rigid anions by means of Dynamical Mechanical Analysis (DMA). We are able to relate the DMA results to the rheological and transport properties provided by viscosity, conductivity, and diffusion coefficient measurements. A good agreement is found in the temperature dependence of different variables described by the Vogel-Fulcher-Tammann model. In particular, the mechanical spectra of all the measured liquids showed the occurrence of a relaxation, for which the analysis suggested its attribution to a diffusive process, which becomes evident when the ion dynamics are not affected by the fast structural reorganization of flexible anions on a local level.
Collapse
Affiliation(s)
- Oriele Palumbo
- Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Piazzale A. Moro 5, I-00185 Rome, Italy
| | - Annalisa Paolone
- Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Piazzale A. Moro 5, I-00185 Rome, Italy
| | - Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK
| | - Daniel Rauber
- Department of Chemistry, Saarland University, Campus B 2.2, 66123 Saarbrücken, Germany
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK
| |
Collapse
|
4
|
Cosby T, Stachurski CD, Mantz RA, Trulove PC, Durkin DP. Elucidating the interplay of local and mesoscale ion dynamics and transport properties in aprotic ionic liquids. Phys Chem Chem Phys 2023; 25:6342-6351. [PMID: 36779353 DOI: 10.1039/d2cp05863d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Ion dynamics and charge transport in 1-methyl-3-octylimidazolium ionic liquids with chloride, bromide, tetrafluoroborate, tricyanomethanide, hexafluorophosphate, triflate, tetrachloroaluminate, bis(trifluoromethylsulfonyl)imide, and heptachlorodialuminate anions are investigated by broadband dielectric spectroscopy, rheology, viscometry, and differential scanning calorimetry. A detailed analysis reveals an anion and temperature-dependent separation of characteristic molecular relaxation rates extracted from various representations of the dielectric spectra. The separation in rates extracted from the electric modulus and conductivity formalisms is interpreted as an experimental signature of significant heterogeneity in the local ion dynamics associated with the structural glass transition, viscosity, and dc ion conductivity. It is further found that the degree of dynamic heterogeneity correlates with the strengths of slow dielectric and mechanical relaxations previously attributed to the dynamics of mesoscale solvophobic aggregates. Increasing local dynamic heterogeneity correlates with an increase in the strength of the slow, aggregate dielectric relaxation and a decrease in the strength of the slow, aggregate mechanical relaxation. Accordingly, increasing local dynamic heterogeneity, brought about by change in temperature and/or cation/anion chemical structure, correlates with an increase in the static dielectric permittivities and a decrease in the contribution of aggregate dynamics to the zero-shear viscosities. The established correlation provides a new ability to distinguish between the influence of mesoscale aggregate shape/morphology versus local and mesoscale ion dynamics on the transport properties of ionic liquids.
Collapse
Affiliation(s)
- Tyler Cosby
- Division of Mathematics and Sciences, University of Tennessee Southern, Pulaski, TN, USA.
| | | | | | - Paul C Trulove
- Department of Chemistry, US Naval Academy, Annapolis, MD, USA.
| | - David P Durkin
- Department of Chemistry, US Naval Academy, Annapolis, MD, USA.
| |
Collapse
|
5
|
Modelling Shear Thinning of Imidazolium-based Ionic Liquids. Chem Phys Lett 2023. [DOI: 10.1016/j.cplett.2023.140387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
|
6
|
Philippi F, Rauber D, Palumbo O, Goloviznina K, McDaniel J, Pugh D, Suarez S, Fraenza CC, Padua A, Kay CWM, Welton T. Flexibility is the key to tuning the transport properties of fluorinated imide-based ionic liquids. Chem Sci 2022; 13:9176-9190. [PMID: 36093026 PMCID: PMC9384794 DOI: 10.1039/d2sc03074h] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 07/02/2022] [Indexed: 11/21/2022] Open
Abstract
Ionic liquids are becoming increasingly popular for practical applications such as biomass processing and lithium-ion batteries. However, identifying ionic liquids with optimal properties for specific applications by trial and error is extremely inefficient since there are a vast number of potential candidate ions. Here we combine experimental and computational techniques to determine how the interplay of fluorination, flexibility and mass affects the transport properties of ionic liquids with the popular imide anion. We observe that fluorination and flexibility have a large impact on properties such as viscosity, whereas the influence of mass is negligible. Using targeted modifications, we show that conformational flexibility provides a significant contribution to the success of fluorination as a design element. Contrary to conventional wisdom, fluorination by itself is thus not a guarantor for beneficial properties such as low viscosity.
Collapse
Affiliation(s)
- Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| | - Daniel Rauber
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany
| | - Oriele Palumbo
- Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi Piazzale Aldo Moro 5 00185 Rome Italy
| | | | - Jesse McDaniel
- School of Chemistry and Biochemistry, Georgia Institute of Technology Atlanta Georgia 30332-0400 USA
| | - David Pugh
- Department of Chemistry, King's College London 7 Trinity Street London SE1 1DB UK
| | - Sophia Suarez
- Department of Physics, Brooklyn College of CUNY Brooklyn New York 11210 USA
| | - Carla C Fraenza
- Department of Physics and Astronomy, Hunter College of CUNY New York 10065 USA
| | - Agilio Padua
- Laboratoire de Chimie, École Normale Supérieure de Lyon, CNRS 69364 Lyon France
| | - Christopher W M Kay
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany
- London Centre for Nanotechnology, University College London 17-19 Gordon Street London WC1H 0AH UK
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| |
Collapse
|
7
|
Yamaguchi T. Volume viscosity and ultrasonic relaxation of ethanol-water mixtures studied by molecular dynamics simulations. Phys Chem Chem Phys 2022; 24:12311-12318. [PMID: 35545094 DOI: 10.1039/d2cp00856d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The volume viscosity of ethanol-water mixtures at various compositions was calculated by means of equilibrium molecular dynamics simulations, and the results were compared with acoustic experiments. The volume viscosity exhibited a strong maximum around the ethanol mole fraction of 0.27, which is in agreement with experiments. The relaxation in the 100 ps regime, which had been revealed by ultrasonic spectroscopy, was also reproduced. Analysis of the two-body density and the adiabatic pressure fluctuation demonstrated that the large volume viscosity of the mixture originates from the long-range concentration fluctuation.
Collapse
Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University, Chikusa, Nagoya, 464-8603, Japan.
| |
Collapse
|
8
|
Yamaguchi T. Coupling between Translational Diffusion of a Solute and Dynamics of the Heterogeneous Structure: Higher Alcohols and Ionic Liquids. J Phys Chem B 2022; 126:3125-3134. [PMID: 35438995 DOI: 10.1021/acs.jpcb.2c01053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Translational diffusion of nonpolar monoatomic solutes in a room-temperature ionic liquid and 1-octanol was studied by molecular dynamics simulation. The diffusion coefficient was evaluated in two different ways: (1) from the mean-square displacement of a freely diffusing solute and (2) from the time correlation function of force acting on a fixed solute. The diffusion of the free solute is much greater than the prediction of the Stokes-Einstein (SE) relation when the size of the solute is small, as has been reported by many experimental works. In contrast, the friction on fixed small solutes follows the SE relation. The mechanism of the solute diffusion in both solvents was then analyzed based on the coupling between the translational motion of the solute and the collective dynamics of the heterogeneous intermediate-range structure characteristic to these solvents. Analysis revealed that the coupling is present in all systems, but the relaxation is fast in the cases of free and small solutes. This suggests that the coupling can relax through the motion of the solute when the solute is free and small, while the relaxation of the heterogeneous structure itself is required for large or fixed solutes. The difference in the relaxation dynamics of the friction on the solute and the shear viscosity is explained as the coupling with different dynamic modes of the solvent. Therefore, the validity of the SE relation may not be a good criterion to judge whether the mechanisms of the diffusion and the viscosity are the same or not.
Collapse
Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
| |
Collapse
|
9
|
Kodis G, Ertem MZ, Newton MD, Matyushov DV. Reorganization Energy of Electron Transfer in Ionic Liquids. J Phys Chem Lett 2022; 13:3297-3303. [PMID: 35389644 DOI: 10.1021/acs.jpclett.2c00733] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Bandshape analysis of charge-transfer optical bands in room-temperature ionic liquids (ILs) was performed to extract the reorganization energy of electron transfer. Remarkably, the reorganization energies in ILs are close to those in cyclohexane. This result runs against common wisdom in the field since conducting ILs, which are characterized by an infinite static dielectric constant, and nonpolar cyclohexane fall to the opposite ends of the polarity scale based on their dielectric constants. Theoretical calculations employing structure factors of ILs from molecular dynamics simulations support the low values of the reorganization energy. Standard dielectric arguments do not apply to solvation in ILs, and nonergodic reorganization energies are required for a quantitative analysis.
Collapse
Affiliation(s)
- Gerdenis Kodis
- Department of Physics and School of Molecular Sciences, Arizona State University, PO Box 871504, Tempe, Arizona 85287-1504, United States
| | - Mehmed Z Ertem
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Marshall D Newton
- Chemistry Division, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Dmitry V Matyushov
- Department of Physics and School of Molecular Sciences, Arizona State University, PO Box 871504, Tempe, Arizona 85287-1504, United States
| |
Collapse
|
10
|
Philippi F, Rauber D, Eliasen KL, Bouscharain N, Niss K, Kay CWM, Welton T. Pressing matter: why are ionic liquids so viscous? Chem Sci 2022; 13:2735-2743. [PMID: 35340854 PMCID: PMC8890108 DOI: 10.1039/d1sc06857a] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Accepted: 02/06/2022] [Indexed: 01/09/2023] Open
Abstract
Room temperature ionic liquids are considered to have huge potential for practical applications such as batteries. However, their high viscosity presents a significant challenge to their use changing from niche to ubiquitous. The modelling and prediction of viscosity in ionic liquids is the subject of an ongoing debate involving two competing hypotheses: molecular and local mechanisms versus collective and long-range mechanisms. To distinguish between these two theories, we compared an ionic liquid with its uncharged, isoelectronic, isostructural molecular mimic. We measured the viscosity of the molecular mimic at high pressure to emulate the high densities in ionic liquids, which result from the Coulomb interactions in the latter. We were thus able to reveal that the relative contributions of coulombic compaction and the charge network interactions are of similar magnitude. We therefore suggest that the optimisation of the viscosity in room temperature ionic liquids must follow a dual approach.
Collapse
Affiliation(s)
- Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| | - Daniel Rauber
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany
| | - Kira Lieberkind Eliasen
- "Glass and Time", IMFUFA, Department of Science and Environment, Roskilde University P.O. Box 260 DK-4000 Roskilde Denmark
| | | | - Kristine Niss
- "Glass and Time", IMFUFA, Department of Science and Environment, Roskilde University P.O. Box 260 DK-4000 Roskilde Denmark
| | - Christopher W M Kay
- Department of Chemistry, Saarland University Campus B2.2 Saarbrücken Germany.,London Centre for Nanotechnology, University College London 17-19 Gordon Street London WC1H 0AH UK
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| |
Collapse
|
11
|
Amith WD, Araque JC, Margulis CJ. Relationship between the Relaxation of Ionic Liquid Structural Motifs and That of the Shear Viscosity. J Phys Chem B 2021; 125:6264-6271. [PMID: 34097825 PMCID: PMC8279556 DOI: 10.1021/acs.jpcb.1c03105] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
In a set of recent
articles, we have highlighted that friction
is highly inhomogeneous in a typical ionic liquid (IL) with charge
networks that are stiff and charge-depleted regions that are soft.
This has consequences not only for the dynamics of ILs but also for the transport properties of solutes
dissolved in them. In this article, we explore whether the family
of alkylimidazolium ILs coupled with bis(trifluoromethylsulfonyl)imide
(with similar Coulombic interactions but different alkyl tails), when
dynamically “equalized” by having a similar shear viscosity,
display q-dependent structural relaxation time scales
that are the same across the family. Our results show that this is
not the case, and in fact, the relaxation of in-network charge alternation
appears to be significantly affected by the presence of separate polar
and apolar domains. However, we also find that if one was to assign
weight factors to the relaxation of the structural motifs, charge
alternation always contributes about the same amount (between 62.1
and 66.3%) across systems to the running integral of the stress tensor
correlation function from which the shear viscosity is derived. Adjacency
correlations between positive and negative moieties also contribute
an identical amount if a prepeak is not present (about 38%) and a
slightly smaller amount (about 28%) when intermediate range order
exists. The prepeak only contributes about 6% to viscoelastic relaxation,
highlighting that the dynamics of the smaller scale motifs is the
most important.
Collapse
Affiliation(s)
| | - Juan C Araque
- School of Engineering, Benedictine College, Atchison, Kansas 66002, United States
| | - Claudio J Margulis
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| |
Collapse
|
12
|
Wang YL, Li B, Sarman S, Mocci F, Lu ZY, Yuan J, Laaksonen A, Fayer MD. Microstructural and Dynamical Heterogeneities in Ionic Liquids. Chem Rev 2020; 120:5798-5877. [PMID: 32292036 PMCID: PMC7349628 DOI: 10.1021/acs.chemrev.9b00693] [Citation(s) in RCA: 197] [Impact Index Per Article: 49.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Indexed: 12/11/2022]
Abstract
Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.
Collapse
Affiliation(s)
- Yong-Lei Wang
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Bin Li
- School
of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai 519082, P. R. China
| | - Sten Sarman
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Francesca Mocci
- Department
of Chemical and Geological Sciences, University
of Cagliari, I-09042 Monserrato, Italy
| | - Zhong-Yuan Lu
- State
Key Laboratory of Supramolecular Structure and Materials, Institute
of Theoretical Chemistry, Jilin University, Changchun 130021, P. R. China
| | - Jiayin Yuan
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Aatto Laaksonen
- Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 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
| | - Michael D. Fayer
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
| |
Collapse
|
13
|
Ghorai PK, Matyushov DV. Equilibrium Solvation, Electron-Transfer Reactions, and Stokes-Shift Dynamics in Ionic Liquids. J Phys Chem B 2020; 124:3754-3769. [DOI: 10.1021/acs.jpcb.0c01773] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Pradip Kr. Ghorai
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India
| | - Dmitry V. Matyushov
- Department of Physics and School of Molecular Sciences, Arizona State University, PO Box 871504, Tempe, Arizona 85287, United States
| |
Collapse
|
14
|
Amith WD, Araque JC, Margulis CJ. A Pictorial View of Viscosity in Ionic Liquids and the Link to Nanostructural Heterogeneity. J Phys Chem Lett 2020; 11:2062-2066. [PMID: 32079397 DOI: 10.1021/acs.jpclett.0c00170] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Prototypical ionic liquids (ILs) are characterized by three structural motifs associated with (1) vicinal interactions, (2) the formation of positive-negative charge-alternating chains or networks, and (3) the alternation of these networks with apolar domains. In recent articles, we highlighted that the friction and mobility in these systems are nowhere close to being spatially homogeneous. This results in what one could call mechanical heterogeneity, where charge networks are intrinsically stiff and charge-depleted regions are softer, flexible, and mobile. This Letter attempts to provide a clear and visual connection between friction-associated with the dynamics of the structural motifs (in particular, the charge network)-and recent theoretical work by Yamaguchi linking the time-dependent viscosity of ILs to the decay of the charge alternation peak in the dynamic structure function. We propose that charge blurring associated with the loss of memory of where positive and negative charges are within networks is the key mechanism associated with viscosity in ILs. An IL will have low viscosity if a characteristic charge-blurring decorrelation time is low. With this in mind, engineering new low-viscosity ILs is reduced to understanding how to minimize this quantity.
Collapse
Affiliation(s)
| | - Juan C Araque
- School of Engineering, Benedictine College, Atchison, Kansas 66002, United States
| | - Claudio J Margulis
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| |
Collapse
|
15
|
Cosby T, Kapoor U, Shah JK, Sangoro J. Mesoscale Organization and Dynamics in Binary Ionic Liquid Mixtures. J Phys Chem Lett 2019; 10:6274-6280. [PMID: 31560210 DOI: 10.1021/acs.jpclett.9b02478] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The impact of mesoscale organization on dynamics and ion transport in binary ionic liquid mixtures is investigated by broad-band dielectric spectroscopy, dynamic-mechanical spectroscopy, X-ray scattering, and molecular dynamics simulations. The mixtures are found to form distinct liquids with macroscopic properties that significantly deviate from weighted contributions of the neat components. For instance, it is shown that the mesoscale morphologies in ionic liquids can be tuned by mixing to enhance the static dielectric permittivity of the resulting liquid by as high as 100% relative to the neat ionic liquid components. This enhancement is attributed to the intricate role of interfacial dynamics associated with the changes in the mesoscopic aggregate morphologies in these systems. These results demonstrate the potential to design the physicochemical properties of ionic liquids through control of solvophobic aggregation.
Collapse
Affiliation(s)
- Tyler Cosby
- Department of Chemical and Biomolecular Engineering , University of Tennessee , Knoxville , Tennessee 37996 , United States
| | - Utkarsh Kapoor
- School of Chemical Engineering , Oklahoma State University , Stillwater , Oklahoma 74078 , United States
| | - Jindal K Shah
- School of Chemical Engineering , Oklahoma State University , Stillwater , Oklahoma 74078 , United States
| | - Joshua Sangoro
- Department of Chemical and Biomolecular Engineering , University of Tennessee , Knoxville , Tennessee 37996 , United States
| |
Collapse
|
16
|
Yamaguchi T. Shear Thinning and Nonlinear Structural Deformation of Ionic Liquids with Long Alkyl Chains Studied by Molecular Dynamics Simulation. J Phys Chem B 2019; 123:6260-6265. [PMID: 31259551 DOI: 10.1021/acs.jpcb.9b03557] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nonequilibrium molecular dynamics (MD) simulation was performed on imidazolium-based ionic liquids of two different alkyl chain lengths, and shear-rate-dependent viscosity was evaluated. Compared with the frequency-dependent linear shear viscosity determined by equilibrium MD simulation, shear thinning occurs at the shear rate several times lower than that predicted by the Cox-Merz rule. The deformation of the structure factor was also evaluated as the function of shear rate. The onset of shear thinning corresponds to that of the nonlinearity in the deformation of the charge-alternation mode in both ionic liquids, which is in harmony with the result of our previous work that the shear relaxation of ionic liquids is mainly coupled to the structural relaxation of the charge-alternation mode. In the presence of the polar-nonpolar domain structure characteristic to ionic liquids with a long alkyl chain, in particular, the nonlinearity in the domain mode begins within the Newtonian regime of shear viscosity.
Collapse
Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering , Nagoya University , Furo-cho, Chikusa, Nagoya , Aichi 464-8603 , Japan
| |
Collapse
|
17
|
Yamaguchi T, Kikuzawa T. High-frequency shear viscosity and ionic mobility of solutions of polyethylene glycol in ionic liquids. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.04.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
18
|
Pabst F, Gabriel J, Blochowicz T. Mesoscale Aggregates and Dynamic Asymmetry in Ionic Liquids: Evidence from Depolarized Dynamic Light Scattering. J Phys Chem Lett 2019; 10:2130-2134. [PMID: 30978281 DOI: 10.1021/acs.jpclett.9b00686] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Nanoscale structures in ionic liquids (ILs) are usually identified by X-ray or neutron scattering techniques and occur when the alkyl chains of the cations are long enough to show the tendency to segregate into apolar domains. In search of dynamic evidence for these nanostructures, different experimental techniques recently reported bimodal dynamic susceptibility spectra. In all cases, the faster process observed was ascribed to the structural α-relaxation and the slower one to the relaxation of long-lived aggregates. By contrast, we show by depolarized dynamic light scattering (DDLS) experiments on a systematic series of imidazolium-based ILs that the dynamics of the cation and anion are clearly separated for long alkyl chains. Therefore, the observation of a bimodal behavior is not related to any nanostructure but reflects the two-component nature of ILs. Thus, a consistent picture is obtained across different experimental methods, like dielectric and shear mechanical relaxation. Finally, the actual dynamic signature of nanostructures is identified for the first time as a weak feature in some of the DDLS spectra at even lower frequencies.
Collapse
Affiliation(s)
- Florian Pabst
- Institut für Festkörperphysik , Technische Universität Darmstadt , 64289 Darmstadt , Germany
| | - Jan Gabriel
- Institut für Festkörperphysik , Technische Universität Darmstadt , 64289 Darmstadt , Germany
| | - Thomas Blochowicz
- Institut für Festkörperphysik , Technische Universität Darmstadt , 64289 Darmstadt , Germany
| |
Collapse
|
19
|
Yamaguchi T, Matsuoka T. Translation-orientation coupling and Cox-Merz rule of liquid hexane. J Chem Phys 2018; 149:204502. [PMID: 30501258 DOI: 10.1063/1.5051680] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Equilibrium and non-equilibrium molecular dynamics simulations are performed on liquid hexane in order to clarify the origin of the Cox-Merz rule of liquids composed of chain-like molecules. The relation between the frequency-dependent complex shear viscosity and the shear-rate dependent nonlinear viscosity follows the Cox-Merz rule as expected. The slowest viscoelastic relaxation mode is explained by the translation-orientation coupling mechanism, and the saturation of the shear-induced orientational order is observed in the non-equilibrium simulation at the onset of the shear thinning. The origin of the Cox-Merz rule is discussed in terms of the translation-orientation coupling.
Collapse
Affiliation(s)
- Tsuyoshi Yamaguchi
- Graduate School of Engineering, Nagoya University, Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan
| | - Tatsuro Matsuoka
- Graduate School of Engineering, Nagoya University, Furo-cho B2-3 (611), Chikusa, Nagoya, Aichi 464-8603, Japan
| |
Collapse
|
20
|
Araque JC, Margulis CJ. In an ionic liquid, high local friction is determined by the proximity to the charge network. J Chem Phys 2018; 149:144503. [PMID: 30316258 DOI: 10.1063/1.5045675] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Structural heterogeneity in Ionic Liquids (ILs) is to a large extent defined by nanoscale apolar pockets that act as spacers between strings of positive and negative charges that alternate. In contrast to this, recent work from our group and that of others appear to indicate that dynamic, energetic, and mechanical heterogeneities are governed by the charged part of the liquid. In this article, we study the dynamics of methane, a small apolar solute, in the family of ILs 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ( Im 1 , n + /NTf2 -), with n = 2, 4, 8 at temperatures that make the viscosity for each liquid similar and around 8 cP. We do this in an attempt to equalize the effect of the solvent on the dynamics of the solute. In all cases, we find that solute proximity to charge-enhanced regions coincides with translationally caged regimes (high local friction) whereas the opposite is true in charge-depleted regions. In a way, these ILs behave like a liquid within a liquid where the charge network is the high friction component.
Collapse
Affiliation(s)
- Juan C Araque
- School of Engineering, Benedictine College, Atchison, Kansas 66002, USA
| | | |
Collapse
|