The Phenomenological Account for Electronic Polarization in Ionic Liquid (original) (raw)
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The Journal of Chemical Physics, 2008
The influences of two different commonly employed force fields on statical and dynamical properties of ionic liquids are investigated for ͓EMIM͔͓BF 4 ͔. The force fields compared in this work are the one of Canongia Lopes and Padua ͓J. Phys. Chem. B 110, 19586 ͑2006͔͒ and that of Liu et al. ͓J. Phys. Chem. B 108, 12978 ͑2004͔͒. Differences in the strengths of hydrogen bonds are found, which are also reflected in the static ion distributions around the cation. Moreover, due to the stronger hydrogen bonding in the force field of Liu et al., the diffusive motions of cations and anions and the rotational behavior of the cations are slower compared with those obtained with the force field of Canongia Lopes and Padua. Both force fields underestimate the zero-field electrical conductivity, while the experimental dielectric constant can be reproduced within the expected statistical error boundaries. J 2 ͘, we follow the method described in Ref. 63. ͗M ជ D 2 ͘ is computed by direct averaging over the MD, while ͗M ជ J 2 ͘ is obtained with the Einstein-Helfand method, which allows to determine the conductivity and ͗M ជ J 2 ͘ from the MSD of M ជ J , ͓͗M ជ J ͑t͒ − M ជ J ͑0͔͒ 2 ͘ = 6Vk B Tt + 2͗M ជ J 2 ͘. ͑19͒
2011
Recently, we introduced a new force field (FF) to simulate transport properties of imidazolium-based room-temperature ionic liquids (RTILs) using a solid physical background. In the present work, we apply this FF to derive thermodynamic, structure, and transport properties of the mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and acetonitrile (ACN) over the whole composition range. Three approaches to derive a force field are formulated based on different treatments of the ion-ion and ion-molecule Coulomb interactions using unit-charge, scaled-charge and floating-charge approaches. The simulation results are justified with the help of experimental data on specific density and shear viscosity for these mixtures. We find that a phenomenological account (particularly, simple scaled-charge model) of electronic polarization leads to the best-performing model. Remarkably, its validity does not depend on the molar fraction of [BMIM][BF4] in the mixture. The derived...
Physical Chemistry Chemical Physics, 2011
A new, non-polarizable force field model (FFM) for imidazolium-based, room-temperature ionic liquids (RTILs), 1-ethyl-3-methyl-imidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate, has been developed. Modifying the FFM originally designed by Liu et al. (J. Phys. Chem. B, 2004, 108, 12978-12989), the electrostatic charges on interacting sites are refined according to partial charges calculated by explicit-ion density functional theory. The refined FFM reproduces experimental heats of vaporization, diffusion coefficients, ionic conductivities, and shear viscosities of RTILs, which is a significant improvement over the original model (Zh. Liu, Sh. Huang and W. Wang, J. Phys. Chem. B, 2004, 108, 12978-12989). The advantages of the proposed procedure include clarity, simplicity, and flexibility. Expanding the functionality of our FFM conveniently only requires modification of the electrostatic charges. Our FFM can be extended to other classes of RTILs as well as condensed matter systems in which the ionic interaction requires an account of polarization effects.
The Journal of chemical …, 2008
The influences of two different commonly employed force fields on statical and dynamical properties of ionic liquids are investigated for ͓EMIM͔͓BF 4 ͔. The force fields compared in this work are the one of Canongia Lopes and Padua ͓J. Phys. Chem. B 110, 19586 ͑2006͔͒ and that of Liu et al. ͓J. Phys. Chem. B 108, 12978 ͑2004͔͒. Differences in the strengths of hydrogen bonds are found, which are also reflected in the static ion distributions around the cation. Moreover, due to the stronger hydrogen bonding in the force field of Liu et al., the diffusive motions of cations and anions and the rotational behavior of the cations are slower compared with those obtained with the force field of Canongia Lopes and Padua. Both force fields underestimate the zero-field electrical conductivity, while the experimental dielectric constant can be reproduced within the expected statistical error boundaries. J 2 ͘, we follow the method described in Ref. 63. ͗M ជ D 2 ͘ is computed by direct averaging over the MD, while ͗M ជ J 2 ͘ is obtained with the Einstein-Helfand method, which allows to determine the conductivity and ͗M ជ J 2 ͘ from the MSD of M ជ J , ͓͗M ជ J ͑t͒ − M ជ J ͑0͔͒ 2 ͘ = 6Vk B Tt + 2͗M ជ J 2 ͘. ͑19͒
The Journal of Chemical Physics, 2018
We study ionic liquids composed 1-alkyl-3-methylimidazolium cations and bis(trifluoromethylsulfonyl)imide anions ([CnMIm][NTf2]) with varying chain-length n = 2, 4, 6, 8 by using molecular dynamics simulations. We show that a reparametrization of the dihedral potentials as well as charges of the [NTf2] anion leads to an improvment of the force field model introduced by Köddermann et al. [ChemPhysChem, 8, 2464 (2007)] (KPL-force field). A crucial advantage of the new parameter set is that the minimum energy conformations of the anion (trans and gauche), as deduced from ab initio calculations and Raman experiments, are now both well represented by our model. In addition, the results for [CnMIm][NTf2] show that this modification leads to an even better agreement between experiment and molecular dynamics simulation as demonstrated for densities, diffusion coefficients, vaporization enthalpies, reorientational correlation times, and viscosities. Even though we focused on a better representation of the anion conformation, also the alkyl chain-length dependence of the cation behaves closer to the experiment. We strongly encourage to use the new NGKPL force field for the [NTf2] anion instead of the earlier KPL parameter set for computer simulations aiming to describe the thermodynamics, dynamics and also structure of imidazolium based ionic liquids.
Angewandte Chemie International Edition, 2003
Room temperature ionic liquids (RTILs) have been considered as a "green", recyclable alternative to the traditional volatile organic solvents because of their chemical and physical properties, such as being liquid at room temperature, air and moisture stability, high solubility power, and virtually no vapor pressure. Being hygroscopic, RTILs can absorb a significant amount of water. Their properties (e.g., solubility, polarity, viscosity, and conductivity) are not only changed by, but also are dependent on the amount of absorbed water. [3] Rates of chemical reactions and efficiencies of various processes in RTILs are, therefore, dependent on absorbed water. As a consequence, information on the structures of RTILs and their interactions with water are important not only fundamentally but also for various industrial applications. Various studies have been made using either experimental techniques, such as FT-IR, Near-IR, fluorescence, viscosimetry, conductivity, and pulsed-gradient spin-echo NMR diffusion coefficient measurements, [3, or theoretical calculations. Unfortunately, these techniques cannot provide direct information on the molecular level of structure of RTILs and their interactions with water. Herein we present direct experimental evidence of cation-cation, cation-water, and cation-anion interactions by NMR spectroscopy through intermolecular nuclear Overhauser enhancements (NOEs) on the model compound 1-n-butyl-3-methylimidazolium tetrafluoborate ([BMIm] + [BF 4 ] À (1), ). Cationcation interactions were investigated by homonuclear NOEs in the rotating frame (ROEs). The ROEs pattern of the pure liquid (1 a) was compared with those of samples containing known amounts of water (1 b-g, ). Water was added to change the structure of the pure ionic liquid by introducing water-cation interactions. As a complementary picture, intermolecular water-cation ROEs were also observed and evaluated to provide details of 1) the type of water-cation interactions and 2) the site of interaction. Eventually, the role of the anion was investigated by heteronuclear steady-state 1 H{ 19 F} NOE difference spectra.
The Journal of …, 2008
Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and Pádua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM + is studied in the presence of three different anions, namely, chloride Cl -, tetrafluoroborate B F 4 -, and bis((trifluoromethyl)sulfonyly)imide TF 2 N -. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF 4 ] to [EMIM][TF 2 N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF 2 N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM] [BF 4 ] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.
Structure and Dynamics of Benzyl-NX 3 (X = Me, Et) Trifluoromethanesulfonate Ionic Liquids
The Journal of Physical Chemistry B, 2014
Ammonium-based benzyl-NX 3 (X = methyl, ethyl) trifluoromethanesulfonate (TFA) ionic liquids (ILs) are low cost, nontoxic, thermally stable ion-conducting electrolytes in fuel cells and batteries. In the present study, we have characterized the structure and dynamics of these ILs using molecular dynamics (MD) simulations and ionic conductivity using electro-chemical impedance spectroscopy (EIS) at varying temperature and relative humidity (RH). Results from MD simulations predict that cation−cation and cation− anion interactions are stronger in benzyltrimethylammonium (BzTMA) compared to benzyltriethylammonium (BzTEA) that diminish with increase in RH. Further, the BzTMA cations show both C−H/Ph (center of mass of phenyl ring) and cation-Ph interactions whereas BzTEA cations show only strong cation-Ph interactions. The C−H/Ph interactions (ψ ≥ 90°, d H-Ph ≤ 4 Å, θ < 50°and d C-Ph ≤ 4.3 Å) in BzTMA cations increase with RH and are highest at RH = 90%. The cumulative impact of electrostatic, cation/Ph, and C−H/Ph interactions results in lower conductivity of BzTMA-TFA IL compared to BzTEA-TFA IL. The EIS measurements show that the trends in ionic conductivity of ILs at RH = 30 and 90% are qualitatively similar to the Nernst−Einstein conductivity from MD simulations. The ionic conductivity of BzTEA-TFA IL is ∼3 times higher than BzTMA-TFA IL at 353 K and RH = 90%.
The Journal of Physical Chemistry B, 2011
In this article, we present evolutionary models to predict the octanolÀwater partition coefficients (log P), water solubilities, and critical micelle concentrations (CMCs) of ionic liquids (ILs), as well as the anionic activity coefficients and hydrophobicities in pure water and octanolÀwater. They are based on a polyparameter linear free energy relationship (LFER) using measured and/or DFT-calculated LFER parameters: hydrogen-bonding acidity (A), hydrogen-bonding basicity (B), polarizability/dipolarity (S), excess molar refraction (E), and McGowan volume (V) of IL ions. With both calculated or experimental LFER descriptors of IL ions, the physicochemical parameters were predicted with an errors of 0.182À0.217 for the octanolÀwater partition coefficient and 0.131À0.166 logarithmic units for the water solubility. Because experimentally determined solute parameters of anions are not currently available, the CMC, anionic activity coefficient, and hydrophobicity were predicted with quantum-chemical methods with R 2 values of at least 0.99, as well as errors below 0.168 logarithmic units. These new approaches will facilitate the assessment of the technical applicability and environmental fate of ionic compounds even before their synthesis. B dx.doi.org/10.1021/jp200042f |J. Phys. Chem. B XXXX, XXX, 000-000