The Chemical Environment of Ionic Liquids: Links Between Liquid Structure, Dynamics, and Solvation

Kobrak, Mark N.

doi:10.1002/9780470259498.ch2

Cited by 25 publications

(22 citation statements)

References 253 publications

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“…Room temperature ionic liquids (ILs), normally composed of organic cations and anions, are potentially important solvents and electrolytes for use in a variety of different applications . Because of the numerous combinations of different organic ions and functional variants thereof, ILs are potential “designer” solvents, as their properties can be adjusted by employing different constituent molecules . It is therefore of practical importance to develop a molecular-level understanding of the properties of ILs in order to more effectively design and utilize them for present and future applications .…”

Section: Introductionmentioning

confidence: 99%

Ab Initio Force Fields for Imidazolium-Based Ionic Liquids

et al. 2016

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We develop ab initio force fields for alkylimidazolium-based ionic liquids (ILs) that predict the density, heats of vaporization, diffusion, and conductivity that are in semiquantitative agreement with experimental data. These predictions are useful in light of the scarcity of and sometimes inconsistency in experimental heats of vaporization and diffusion coefficients. We illuminate physical trends in the liquid cohesive energy with cation chain length and anion. These trends are different than those based on the experimental heats of vaporization. Molecular dynamics prediction of the room temperature dynamics of such ILs is more difficult than is generally realized in the literature due to large statistical uncertainties and sensitivity to subtle force field details. We believe that our developed force fields will be useful for correctly determining the physics responsible for the structure/property relationships in neat ILs.

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Section: Introductionmentioning

confidence: 99%

Ab Initio Force Fields for Imidazolium-Based Ionic Liquids

et al. 2016

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“…6,7 With this experience we have turned to ionic liquids. Due to the broad range of applications of ionic liquids, [19][20][21][22] for which knowledge of transport coefficients is of great importance, there are several reports on their diffusion coefficients measured by means of PFG NMR; [23][24][25][26][27] At this stage one should stress that PFG NMR measures self-diffusion coefficient of the molecule (or ion), while FC NMR probes the relative diffusion coefficient, D 12 = D 1 + D 2 , where D 1 , D 2 are self-diffusion coefficients of the participating species (for identical molecules D 12 = 2D). The relaxation studies on molecular liquids have been carried out for protons ( 1 H).…”

Section: Introductionmentioning

confidence: 99%

Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry

Kruk

Meier

Rachocki

et al. 2014

The Journal of Chemical Physics

125

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Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(ω) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids.

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“…1 for a schematic of the system). Related ideas of ion association have been employed in [13][14][15][16] to study criticality To determine the fraction of free ions, α, we consider a "chemical" equilibrium between free ions and ion pairs, which we define as ions being held at closest approach cation + anion cation − anion.…”

mentioning

confidence: 99%

“…1 for a schematic of the system). Related ideas of ion association have been employed in [13][14][15][16] to study criticality and the gas-liquid transition in Coulomb fluids.…”

mentioning

confidence: 99%

Are Room-Temperature Ionic Liquids Dilute Electrolytes?

Lee

Vella

Perkin

et al. 2014

J. Phys. Chem. Lett.

137

143

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An important question in understanding the structure of ionic liquids is whether ions are truly "free" and mobile, which would correspond to a concentrated ionic melt, or are rather "bound" in ion pairs, that is, a liquid of ion pairs with a small concentration of free ions. Recent surface force balance experiments from different groups have given conflicting answers to this question. We propose a simple model for the thermodynamics and kinetics of ion pairing in ionic liquids. Our model takes into account screened ion-ion, dipole-dipole, and dipole-ion interactions in the mean-field limit. The results of this model suggest that almost two-thirds of the ions are free at any instant, and ion pairs have a short lifetime comparable to the characteristic time scale for diffusion. These results suggest that there is no particular thermodynamic or kinetic preference for ions to reside in pairs. We therefore conclude that ionic liquids are concentrated, rather than dilute, electrolytes.

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The Chemical Environment of Ionic Liquids: Links Between Liquid Structure, Dynamics, and Solvation

Cited by 25 publications

References 253 publications

Ab Initio Force Fields for Imidazolium-Based Ionic Liquids

Ab Initio Force Fields for Imidazolium-Based Ionic Liquids

Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry

Are Room-Temperature Ionic Liquids Dilute Electrolytes?

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