Electrical conductivity and translational diffusion in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Redox potentials in ionic liquids: Anomalous behavior?

Redox potentials depend on the nature of the solvent/electrolyte through the solvation energies of the ionic solute species. For concentrated electrolytes, ion solvation may deviate significantly from the Born model predictions due to ion pairing and correlation effects. Recently, Ghorai and Matyushov [J. Phys. Chem. B 124, 3754-3769 (2020)] predicted, on the basis of linear response theory, an anomalous trend in the solvation energies of room temperature ionic liquids, with deviations of hundreds of kJ/mol from the Born model for certain size solutes/ions. In this work, we computationally evaluate ionic solvation energies in the prototypical ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM/BF4), to further explore this behavior and benchmark several of the approximations utilized in the solvation energy predictions. For comparison, we additionally compute solvation energies within acetonitrile and molten NaCl salt to illustrate the limiting behavior of purely dipolar and ionic solvents. We find that the overscreening effect, which results from the inherent charge oscillations of the ionic liquid, is substantially reduced in magnitude due to screening from the dipoles of the molecular ions. Therefore, for the molten NaCl salt, for which the ions do not have permanent dipoles, modulation of ionic solvation energies from the overscreening effect is most significant. The conclusion is that ionic liquids do indeed exhibit unique solvation behavior due to peak(s) in the electrical susceptibility caused by the ion shell structure; redox potential shifts for BMIM/BF4 are of more modest order ∼0.1 V, but may be larger for other ionic liquids that approach molten salt behavior.

Molecular Dynamics Simulation on the Charge Transport Properties in a Salt-in-Ionic Liquid Electrolyte

A clear picture of charge transport properties in salt-in-ionic liquid electrolyte (SILE) is indispensable for the applications in lithium-ion batteries. In this study, we applied molecular dynamics (MD) simulations on a typical SILE system, composed of lithium bis(fluorosulfonyl)imide (LiFSI) with a molar fraction of 0.3 doped in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI). Based on the MD simulations, we calculated conductivity spectra from 108 Hz to 1014 Hz, charge current correlation functions, and charge mean square displacements, based on the center-of-mass (COM) velocities of the ions. The conductivity spectra show a bimodal feature between 1012 Hz and 1013 Hz, attributed to the interionic vibrations of the EMIM+-FSI- and Li+-FSI- contact ion pairs, respectively. Structural relaxation is observed between 109 Hz and 1012 Hz, and a flat plateau below 109 Hz, attributed to the direct current (DC) conductivity. For this SILE composed of three constituent ions, i.e., Li+, EMIM+, and FSI-, the above transport properties are further partitioned to the contributions of the individual constituent ions, including self, distinct contribution of the same constituent ions, and also the cross correlation between them. Detailed analyses on the individual contributions reveal strongly correlated motions in this complex ionic system.

Molecular Insight into the Ionic Conduction of Quaternary Ammonium and Phosphonium Cation-Based Ionic Liquids Using Dielectric and Spectroscopy Analyses

We analyzed the primary properties of ionic liquids (ILs) comprising quaternary phosphonium cations and bis(trifluoromethylsulfonyl) amide anions and compared them with those of corresponding quaternary-ammonium-cation-based ILs. Broadband dielectric spectroscopy was used to confirm the coupling between the translational and orientational motions of ions, and our results demonstrated that the high ionic conductivity of the phosphonium-based ILs was attributed to their fast rotational dynamics. The differences between ILs with different cations were further evaluated using vibrational (Raman and terahertz) spectroscopy. The Raman spectroscopy data revealed that the cation structure affected the conformation and flexibility (conformational change) of the anion. Furthermore, terahertz spectroscopy allowed us to evaluate the relationship between ion transport and intermolecular interactions between the cation and anion of ILs.

Collectivity in ionic liquids: a temperature dependent, polarizable molecular dynamics study

We use polarizable molecular dynamics simulations to study the thermal dependence of both structural and dynamic properties of two ionic liquids sharing the same cation (1-ethyl-3-methylimidazolium). The linear temperature trend in the structure is accompanied by an exponential Arrhenius-like behavior of the dynamics. Our parameter-free Voronoi tessellation analysis directly casts doubt on common concepts such as the alternating shells of cations and anions and the ionicity. The latter tries to explain the physico-chemical properties of the ionic liquids based on the association and dissociation of an ion pair. However, cations are in the majority of both ion cages, around cations and around anions. There is no preference of a cation for a single anion. Collectivity is a key factor in the dynamic properties of ionic liquids. Consequently, collective rotation relaxes faster than single-particle rotations, and the activation energies for collective translation and rotation are lower than those of the single molecules.

Low-frequency dynamics in ionic liquids: Comparison of experiments and the random barrier model

By examining the fine features of dielectric spectra of ionic liquids, we show that the derivative of real permittivity progressively broadens at low frequencies when the glass transition is approached...

The effect of thermal treatment on ac/dc conductivity and current fluctuations of PVDF/NMP/[EMIM][TFSI] solid polymer electrolyte

The experimental study deals with the investigation of the effect of diverse crystallinity of imidazolium ionic-liquid-based SPE on conductivity and current fluctuations. The experimental study was carried out on samples consisting of [EMIM][TFSI] as ionic liquid, PVDF as a polymer matrix and NMP as a solvent. After the deposition, the particular sample was kept at an appropriate temperature for a specific time in order to achieve different crystalline forms of the polymer in the solvent, since the solvent evaporation rate controls crystallization. The ac/dc conductivities of SPEs were investigated across a range of temperatures using broadband dielectric spectroscopy in terms of electrical conductivity. In SPE samples of the higher solvent evaporation rate, the real parts of conductivity spectra exhibit a sharper transition during sample cooling and an increase of overall conductivity, which is implied by a growing fraction of the amorphous phase in the polymer matrix in which the ionic liquid is immobilized. The conductivity master curves illustrate that the changing of SPEs morphology is reflected in the low frequency regions governed by the electrode polarization effect. The dc conductivity of SPEs exhibits Vogel–Fulcher–Tammann temperature dependence and increases with the intensity of thermal treatment. Spectral densities of current fluctuations showed that flicker noise, thermal noise and shot noise seems to be major noise sources in all samples. The increase of electrolyte conductivity causes a decrease in bulk resistance and partially a decrease in charge transfer resistance, while also resulting in an increase in shot noise. However, the change of electrode material results in a more significant change of spectral density of current fluctuations than the modification of the preparation condition of the solid polymer electrolyte. Thus, the contact noise is considered to contribute to overall current fluctuations across the samples.

Ion Dissociation in Ionic Liquids and Ionic Liquid Solutions

The extent to which cations and anions in ionic liquids (ILs) and ionic liquid solutions are dissociated is of both fundamental scientific interest and practical importance because ion dissociation has been shown to impact viscosity, density, surface tension, volatility, solubility, chemical reactivity, and many other important chemical and physical properties. When mixed with solvents, ionic liquids provide the unique opportunity to investigate ion dissociation from infinite dilution in the solvent to a completely solvent-free state, even at ambient conditions. The most common way to estimate ion dissociation in ILs and IL solutions is by comparing the molar conductivity determined from ionic conductivity measurements such as electrochemical impedance spectroscopy (EIS) (which measure the movement of only the charged, i.e., dissociated, ions) with the molar conductivity calculated from ion diffusivities measured by pulse field gradient nuclear magnetic resonance spectroscopy (PFG-NMR, which gives movement of all of the ions). Because the NMR measurements are time-consuming, the number of ILs and IL solutions investigated by this method is relatively limited. We have shown that use of the Stokes-Einstein equation with estimates of the effective ion Stokes radii allows ion dissociation to be calculated from easily measured density, viscosity, and ionic conductivity data (ρ, η, λ), which is readily available in the literature for a much larger number of pure ILs and IL solutions. Therefore, in this review, we present values of ion dissociation for ILs and IL solutions (aqueous and nonaqueous) determined by both the traditional molar conductivity/PFG-NMR method and the ρ, η, λ method. We explore the effect of cation and anion alkyl chain length, structure, and interaction motifs of the cation and anion, temperature, and the strength of the solvent in IL solutions.

Modulation of Cation Diffusion by Reversible Supramolecular Assemblies in Ionic Liquid-Based Nanocomposites

Ionic liquid (IL) properties, such as high ionic conductivity under ambient conditions combined with nontoxicity and nonflammability, make them important materials for future technologies. Despite high ion conductivity desired for battery applications, cation transport numbers in ILs are not sufficient enough to attain high power density batteries. Thus, developing novel approaches directed toward improvement of cation transport properties is required for the application of ILs in energy-storing devices. In this effort, we used various experimental techniques to demonstrate that the strategy of mixing ILs with ultrasmall (1.8 nm) nanoparticles (NPs) resulted in melt-processable composites with improved transport numbers for cations at room temperature. This significant enhancement in the transport number was attributed to the specific chemistry of NPs exhibiting a weaker cation and stronger anion coordination at ambient temperature. At high temperature, significantly weakened NP-anion associations promoted a liquid-like behavior of composites, highlighting the melt-processability of these composites. These results show that designing a reversible dynamic noncovalent NP-anion association controlled by the temperature may constitute an effective strategy to control ion diffusion. Our studies provide fundamental insights into mechanisms driving the charge transport and offer practical guidance for the design of melt-processable composites with an improved cation transport number under ambient conditions.

Anions as Dynamic Probes for Ionic Liquid Mixtures

Ionic liquid (IL) mixtures have been proposed as a viable alternative to rationally fine-tune the physicochemical properties of ILs for a variety of applications. The understanding of the effects of mixing ILs on the properties of the mixtures is however only in the very early stages. Two series of ionic liquid mixtures, based on the 1-ethyl-3-methylimidazolium and 1-dodecyl-3-methylimidazolium cations, and having a common anion (tetrafluoroborate or bis(trifluoromethylsulfonyl)imide), have been prepared and deeply characterized via multiple NMR techniques. Diffusion and relaxation methods combined with 2D ion-ion correlation (nuclear Overhauser enhancement) experiments have been used for a better understanding of the interplay between dynamics and structure of IL mixtures. A crucial role of the anion in driving the mixture's behavior emerged, making them important "dynamic probes" for gaining information of the polar and nonpolar regions of ionic liquids and their mixtures.

Evolution of Dielectric Behavior of Regenerated Cellulose Film during Isothermal Dehydration Monitored in Real Time via Dielectric Spectroscopy

The dielectric relaxation behavior of a regenerated cellulose (RC) film during isothermal dehydration was monitored in real time via dielectric spectroscopy, in order to investigate on one hand the influence of water on its dynamics and the variation of microstructure and phase composition during dehydration on the other. The progression of water loss is clearly revealed by the evolution of the dielectric relaxation behavior with drying time, which suggests two distinctly different drying stages separated by a striking transition period. The dielectric relaxation behavior at the first drying stage is found overwhelmingly dominated by ionic motion, and that at the second stage is basically a result of molecular dynamics. The mechanisms of these relaxations are proposed, through which the influence of water on the dynamics of the RC film and the variation of the microstructure and phase composition of the film at different hydration state are discussed in detail. An interesting finding is that highly ordered but noncrystalline arrangement of cellulose molecules exists, but it can be formed only when the film is in specific hydration state. This study demonstrates that dielectric spectroscopy is an effective tool in real-time monitoring kinetic process.

Dynamical properties of a room temperature ionic liquid: Using molecular dynamics simulations to implement a dynamic ion cage model

The transport behavior of ionic liquids (ILs) is pivotal for a variety of applications, especially when ILs are used as electrolytes. Many aspects of the transport dynamics of ILs remain to be understood. Here, a common ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf₂), was studied with molecular dynamics simulations. The results show that BmimNTf₂ displays typical structural relaxation, subdiffusive behavior, and a breakdown of the Stokes-Einstein diffusion relation as in glass-forming liquids. In addition, the simulations show that the translational dynamics, reorientation dynamics, and structural relaxation dynamics are well described by the Vogel-Fulcher-Tammann equation like fragile glass forming liquids. Building on previous work that employed ion cage models, it was found that the diffusion dynamics of the cations and anions were well described by a hopping process random walk where the step time is the ion cage lifetime obtained from the cage correlation function. Detailed analysis of the ion cage structures indicated that the electrostatic potential energy of the ion cage dominates the diffusion dynamics of the caged ion. The ion orientational relaxation dynamics showed that ion reorientation is a necessary step for ion cage restructuring. The dynamic ion cage model description of ion diffusion presented here may have implications for designing ILs to control their transport behavior.

Glassy Dynamics and Translational-Rotational Coupling of an Ionically Conducting Pharmaceutical Salt-Sodium Ibuprofen

In this work, we study the structural dipolar relaxation and ionic conductivity relaxation in an ionized derived from a nonionized glass former. The latter is the salt form of a well-studied active pharmaceutical ingredient, sodium ibuprofen, and the former is ibuprofen. Quantum mechanical calculations were employed to study the variation in its molecular electrostatic potentials, and its spatial extent on its salt formation with Na⁺ ions. Measurements have been made using differential scanning calorimetry and broadband dielectric spectroscopy, and the characterization is assisted by density functional theory. The dielectric data contain information on both ionic and dipolar molecular mobility of NaIb and were extracted by representation in terms of the electric modulus and permittivity. A secondary β-conductivity relaxation coexists with the primary α-conductivity relaxation. By use of the coupling model, we show that the β-conductivity relaxation is connected to the α-conductivity relaxation and is the analogue of the relation of the Johari-Goldstein β-relaxation to the structural α-relaxation, shown valid also in ibuprofen. This remarkable result has an impact on the fundamental understanding of the dynamics of ionic conductivity. By representing the data as permittivity, a dipolar β-relaxation was found to have practically the same relaxation times as the β-conductivity relaxation in the glassy state and translational-rotational coupling is valid at a more local secondary relaxation level. However, the α-conductivity relaxation decouples from structural α-relaxation because the structural glass transition temperature is lower than the conductivity counterpart by 29 K. These are novel findings. The study elucidates the effects on the dynamics by the change in the nature of bonding and in size on introducing sodium ions to ibuprofen in the glassy and supercooled liquid states.

The Interplay between Charge Transport and CO2 Capturing Mechanism in [EMIM][SCN] Ionic Liquid: A Broadband Dielectric Study

The hoisted increment in the CO₂ emission in the atmosphere is a noteworthy environmental problem. Gas-liquid absorption is a well-known strategy that can be used to control CO₂ emissions from an increased rate of fossil fuel industrializations. In this work, a combination of broadband dielectric spectroscopy, Fourier infrared (FTIR) spectroscopy, and quantum chemical calculations were used to study the absorption, desorption and kinetic mechanism of a room temperature imidazolium ionic liquid (IL) with cyanide anion, 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) on CO₂ exposure. Initially, the charge transport and glassy dynamics of [EMIM][SCN] is investigated in a wide frequency and temperature range using broadband dielectric spectroscopy and differential scanning calorimetry. The conductivity relaxation was well fitted with Havriliak-Negami function in the modulus formalism, while the dc conductivity correlated well with the Barton-Nakajima-Namikawa relation. Then, the conductometric approach was taken to monitor the interplay between the ionic conductivity of [EMIM][SCN] and diffusion of captured CO₂ in it. The resistance of the IL increases upon CO₂ exposure, indicating a chemical change at the molecular level of [EMIM][SCN]. The possible CO₂ capturing mechanisms for [EMIM][SCN] were investigated with density functional theory calculations and FTIR spectroscopy. Thus, this work proposes a new strategy to explain the mechanism underlined in chemisorption of CO₂ in the [EMIM][SCN]. This can be extended to more promising CO₂ capturing materials including ionic liquids especially imidazolium-based ionic liquids with cyanide anions like dicyanimide, tricyanometanide, tetracyanoborate, etc.

Ionic transport in nematic liquid crystals and alignment layer effects on electrode polarization

The physical properties of a liquid crystal-ionic liquid system were investigated. Low-frequency dielectric spectroscopy for 4-cyano-4'-pentylbiphenyl (5CB) doped with 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF ₄) for the nematic and isotropic phase of host substances was performed. We obtained electrical conductivity values in the range from 298.2 K to 313.2 K and the conductivity anisotropy was confirmed. Further study of the relaxation process for bmim ⁺ allowed us to extract the relaxation frequencies and amplitudes from experimental data and confirm the temperature scaling; the thickness of the interfacial layers was estimated for the homogeneous and homeotropic alignments of the prepared composite. An attempt to unfold the ion contribution on the charge transport was made in order to better understand the electrode polarization process. In this work, the influence of the alignment layer and phase state on the interfacial layer formation in liquid crystal media will be explained better.

Influence of molecular weight on ion-transport properties of polymeric ionic liquids

We report the results of atomistic molecular dynamics simulations on polymerized 1-butyl-3-vinylimidazolium-hexafluorophosphate ionic liquids, studying the influence of the polymer molecular weight on the ion mobilities and the mechanisms underlying ion transport, including ion-association dynamics, ion hopping, and ion-polymer coordinations. With an increase in polymer molecular weight, the diffusivity of the hexafluorophosphate (PF₆^-) counterion decreases and plateaus above seven repeat units. The diffusivity is seen to correlate well with the ion-association structural relaxation time for pure ionic liquids, but becomes more correlated with ion-association lifetimes for larger molecular weight polymers. By analyzing the diffusivity of ions based on coordination structure, we unearth a transport mechanism in which the PF₆^- moves by "climbing the ladder" while associated with four polymeric cations from two different polymers.

A review of NMR methods used in the study of the structure and dynamics of ionic liquids

Recently, NMR spectroscopy has been emerging out as a powerful tool to study the structure and dynamics of ionic liquids (ILs) and ILs-Li⁺ salt mixtures. This mini-review primarily focuses on the applications of various NMR spectroscopic techniques such as self-diffusion measurements, NMR relaxometry, two-dimensional NMR, and other novel NMR approaches to study the structure and dynamics of ILs and its mixtures with lithium salts. Copyright © 2017 John Wiley & Sons, Ltd.

Dielectric study on mixtures of ionic liquids

Ionic liquids are promising candidates for electrolytes in energy-storage systems. We demonstrate that mixing two ionic liquids allows to precisely tune their physical properties, like the dc conductivity. Moreover, these mixtures enable the gradual modification of the fragility parameter, which is believed to be a measure of the complexity of the energy landscape in supercooled liquids. The physical origin of this index is still under debate; therefore, mixing ionic liquids can provide further insights. From the chemical point of view, tuning ionic liquids via mixing is an easy and thus an economic way. For this study, we performed detailed investigations by broadband dielectric spectroscopy and differential scanning calorimetry on two mixing series of ionic liquids. One series combines an imidazole based with a pyridine based ionic liquid and the other two different anions in an imidazole based ionic liquid. The analysis of the glass-transition temperatures and the thorough evaluations of the measured dielectric permittivity and conductivity spectra reveal that the dynamics in mixtures of ionic liquids are well defined by the fractions of their parent compounds.

Investigation of dynamics in BMIM TFSA ionic liquid through variable temperature and pressure NMR relaxometry and diffusometry

A comprehensive variable temperature, pressure and frequency multinuclear (1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T1 measurements reveal site-dependent interactions in the cation with strengths in the order MD3 > CD3 > CD2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD2 sites having the largest gradient. Additionally, the α saturation effect in T1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.

Dynamic response of a thin sessile drop of conductive liquid to an abruptly applied or removed electric field

We consider, both theoretically and experimentally, a thin sessile drop of conductive liquid that rests on the lower plate of a parallel-plate capacitor. We derive analytical expressions for both the initial deformation and the relaxation dynamics of the drop as the electric field is either abruptly applied or abruptly removed, as functions of the geometrical, electrical, and material parameters, and investigate the ranges of validity of these expressions by comparison with full numerical simulations. These expressions provide a reasonable description of the experimentally measured dynamic response of a drop of conductive ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate.

Proton conductivity and phase transitions in 1,2,3-triazole

1,2,3-Triazole (TR) is a good proton conductor which is tidely related to formation of a hydrogen bond network along the N-HN trajectory and its self-dissociation into diH-1,2,3-triazolium and 1,2,3-triazolate. To gain a deeper understanding, the proton conductivity of TR is measured by impedance spectroscopy (IS) across its melting temperature and an additionally discovered solid-solid phase transition. The orthorhombic high temperature phase and the monoclinic low temperature modification are investigated by polarized optical microscopy, DSC- and WAXS measurements. Furthermore, the diffusion coefficients of TR are determined from IS data and measured by (1)H PFG NMR spectroscopy in the melt which allows for separate evaluation of contributions of proton hopping across the hydrogen bond network and the vehicle mechanism to the proton conductivity where the vehicles are defined as charged species generated by TR self-dissociation. Finally, the degree of dissociation of TR is calculated and the influence of the self-dissociation of TR on the proton conductivity is discussed in the context of the dielectric constant.

Carbon-ionogel supercapacitors for integrated microelectronics

To exceed the performance limits of dielectric capacitors in microelectronic circuit applications, we design and demonstrate on-chip coplanar electric double-layer capacitors (EDLCs), or supercapacitors, employing carbon-coated gold electrodes with ionogel electrolyte. The formation of carbon-coated microelectrodes is accomplished by solution processing and results in a ten-fold increase in EDLC capacitance compared to bare gold electrodes without carbon. At frequencies up to 10 Hz, an areal capacitance of 2.1 pF μm(-2) is achieved for coplanar carbon-ionogel EDLCs with 10 μm electrode gaps and 0.14 mm(2) electrode area. Our smallest devices, comprised of 5 μm electrode gaps and 80 μm(2) of active electrode area, reach areal capacitance values of ∼0.3 pF μm(-2) at frequencies up to 1 kHz, even without carbon. To our knowledge, these are the highest reported values to date for on-chip EDLCs with sub-mm(2) areas. A physical EDLC model is developed through the use of computer-aided simulations for design exploration and optimization of coplanar EDLCs. Through modeling and comparison with experimental data, we highlight the importance of reducing the electrode gap and electrolyte resistance to achieve maximum performance from on-chip EDLCs.

Do TFSA Anions Slither? Pressure Exposes the Role of TFSA Conformational Exchange in Self-Diffusion

Multinuclear ((1)H, (2)H, and (19)F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent (2)H T1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, as shown by their respective activation volumes (28.8 ± 2.5 cm(3)/mol for TFSA vs 14.6 ± 1.3 cm(3)/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV(‡)) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis. In addition, (2)H T1 data suggest increased ordering with increasing pressure, with two T1 regimes observed for the MD3 and D2 isotopologues between 0.1-100 and 100-250 MPa, respectively. The activation volumes for T1 were 21 and 25 cm(3)/mol (0-100 MPa) and 11 and 12 cm(3)/mol (100-250 MPa) for the MD3 and D2 isotopologues, respectively.

Decoupling of ionic conductivity from structural dynamics in polymerized ionic liquids

Charge transport and structural dynamics in low molecular weight and polymerized 1-vinyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) are investigated by a combination of broadband dielectric spectroscopy, dynamic mechanical spectroscopy and differential scanning calorimetry. While the dc conductivity and fluidity exhibit practically identical temperature dependence for the non-polymerized IL, a significant decoupling of ionic conduction from structural dynamics is observed for the polymerized IL. In addition, the dc conductivity of the polymerized IL exceeds that of its molecular counterpart by four orders of magnitude at their respective calorimetric glass transition temperatures. This is attributed to the unusually high mobility of the anions especially at lower temperatures when the structural dynamics is significantly slowed down. A simple physical explanation of the possible origin of the remarkable decoupling of ionic conductivity from structural dynamics is proposed.

Classical density functional theory & simulations on a coarse-grained model of aromatic ionic liquids

A new classical density functional approach is developed to accurately treat a coarse-grained model of room temperature aromatic ionic liquids. Our major innovation is the introduction of charge-charge correlations, which are treated in a simple phenomenological way. We test this theory on a generic coarse-grained model for aromatic RTILs with oligomeric forms for both cations and anions, approximating 1-alkyl-3-methyl imidazoliums and BF₄⁻, respectively. We find that predictions by the new density functional theory for fluid structures at charged surfaces are very accurate, as compared with molecular dynamics simulations, across a range of surface charge densities and lengths of the alkyl chain. Predictions of interactions between charged surfaces are also presented.