Surfactant aggregation within room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

On the basis of the response of solvatochromic probes [Reichardt's betaine dye, pyrene, and 1,3-bis(1-pyrenyl)propane], we have investigated the aggregation behavior of common anionic, cationic, and nonionic surfactants when solubilized within a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (emimTf2N). We observed possible aggregate formation by all nonionic surfactants included in the study (Brij-35, Brij-700, Tween-20, and Triton X-100), while no aggregation was observed for the cationic surfactant cetyltrimethylammonium bromide. The anionic surfactant sodium dodecyl sulfate does not appear to solubilize within emimTf2N at ambient conditions.     

Low-temperature heat capacity of room-temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Heat capacities of liquid, stable crystal, and liquid-quenched glass of a room-temperature ionic liquid (RTIL), 1-hexyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide were measured between 5 and 310 K by adiabatic calorimetry. Heat capacity of the liquid at 298.15 K was determined for an IUPAC project as (631.6 +/- 0.5) J K(-1) mol(-1). Fusion was observed at T(fus) = 272.10 K for the stable crystalline phase, with enthalpy and entropy of fusion of 28.34 kJ mol(-1) and 104.2 J K(-1) mol(-1), respectively. The purity of the sample was estimated as 99.83 mol % by the fractional melting method. The liquid could be supercooled easily and the glass transition was observed around T(g) approximately 183 K, which was in agreement with the empirical relation, T(g) approximately ((2)/(3)) T(fus). The heat capacity of the liquid-quenched glass was larger than that of the crystal as a whole. In the lowest temperature region, however, the difference between the two showed a maximum around 6 K and a minimum around 15 K, at which the heat capacity of the glass was a little smaller than that of crystal.     

Solubility of carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

In this work, the phase behaviour of the binary system of carbon dioxide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N]) has been studied experimentally. The equipment used for the experiments is the Cailletet set-up, based on visual observations of phase transitions of systems with constant overall composition. Results are reported for carbon dioxide concentrations ranging from 12.3 to 59.3 mol%, and within temperature and pressure ranges of 310–450 K and 0–15 MPa, respectively. The data reveal an extremely high capacity of the selected ionic liquid for dissolving CO₂ gas, for example, reaching up to about 60 mol% within the above-mentioned pressure and temperature range. Also, the solubility of CO₂ in the ionic liquid [emim][Tf₂N] is compared to the solubility of CO₂ in the ionic liquid [emim][PF₆], an ionic liquid that shares the same cation.     

Liquid structure of room-temperature ionic liquid, 1-Ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide

The liquid structure of 1-ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide (EMI(+)TFSI(-)) has been studied by means of large-angle X-ray scattering (LAXS), (1)H, (13)C, and (19)F NMR, and molecular dynamics (MD) simulations. LAXS measurements show that the ionic liquid is highly structured with intermolecular interactions at around 6, 9, and 15 A. The intermolecular interactions at around 6, 9, and 15 A are ascribed, on the basis of the MD simulation, to the nearest neighbor EMI(+)...TFSI(-) interaction, the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions, and the second neighbor EMI+...TFSI(-) interaction, respectively. The ionic liquid involves two conformers, C(1) (cis) and C(2) (trans), for TFSI(-), and two conformers, planar cis and nonplanar staggered, for EMI(+), and thus the system involves four types of the EMI(+)...TFSI(-) interactions in the liquid state by taking into account the conformers. However, the EMI(+)...TFSI(-) interaction is not largely different for all combinations of the conformers. The same applies alsoto the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions. It is suggested from the 13C NMR that the imidazolium C(2) proton of EMI(+) strongly interacts with the O atom of the -SO(2)(CF(3)) group of TFSI(-). The interaction is not ascribed to hydrogen-bonding, according to the MD simulation. It is shown that the liquid structure is significantly different from the layered crystal structure that involves only the nonplanar staggered EMI(+) and C(1) TFSI(-) conformers.     

Vapour permeation and sorption in fluoropolymer gel membrane based on ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide

The emissions of hydrocarbons from fossil fuels into atmosphere entail both an economic loss and an environmental pollution. Membrane separations can be used for vapour recovery and/or vapour removal from the permanent gas stream, given that the appropriate membrane is identified. A neat poly(vinylidene fluoride-co-hexafluoropropylene) membrane is impermeable to both the representatives of aliphatic hydrocarbons and branched hydrocarbons, namely hexane and isooctane, whereas the permeation flux is enhanced by the presence of 80 mass % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide in the membrane, as detailed in this work. The permeabilities of hydrocarbon vapours were determined from the binary mixture containing hydrocarbon and nitrogen to simulate the real input of an air stream containing a condensable hydrocarbon. The diffusion coefficient determined from sorption measurements was higher for hexane, as would be expected for a smaller molecule, whereas both the sorption isotherms and permeabilities of the hydrocarbons studied were found to be almost identical. It is possible that the sorption effect predominates in the transport mechanism for VOCs/N₂ separations.     

Supercapacitive performance of porous graphene nanosheets in bis(trifluoromethylsulfony)imide and bis(fluorosulfonyl)imide ionic liquid electrolytes

Journal of Solid State Electrochemistry - A method of high-heating-rate thermal reduction is used to produce porous graphene nanosheets (PGNSs). This material is characterized by a unique holey...     

Ion-pair formation in the ionic liquid 1-ethyl-3-methylimidazolium bis(triflyl)imide as a function of temperature and concentration.

The structures and ion-pair formation in the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are studied by a combination of FTIR measurements and DFT calculations. We could clearly distinguish imidazolium cations that are completely H-bonded to anions from those that are single H-bonded in ion pairs. Ion-pair formation already occurs in the neat IL and rises with temperature. Ion-pair formation is strongly promoted by dilution of the IL in chloroform. In these weakly polar environments ion pairs H-bonded via C(2)H are strongly favored over those H-bonded via C(4,5)H. This finding is in agreement with DFT (gas phase) calculations, which show a preference for ion pairs H-bonded via C(2)H as a result of the acidic C(2)H bond.     

Rotational dynamics of a diatomic solute in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate

Reorientational time correlation functions C(l)(t)( identical withP(l)[cos theta(t)]) for a diatomic solute in 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI(+)PF(6) (-)) are analyzed via molecular dynamics computer simulations, where <...> denotes an equilibrium ensemble average, P(l) the lth order Legendre polynomial and theta(t) the angle between the solute orientation at time t and its initial direction. Overall results are indicative of heterogeneous dynamics in EMI(+)PF(6) (-). For a small nondipolar solute, C(l)(t) are well-described as stretched exponential functions in wide time ranges. One striking feature is that after rapid initial relaxation, C(2)(t) decays more slowly than C(1)(t). As a result, the correlation time associated with the former is considerably longer than that with the latter. This is ascribed to solvent structural fluctuations, which allow large-amplitude solute rotations. As the solute size grows, relaxation of C(l)(t) approaches exponential decay.     

Changes of the near-surface chemical composition of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide room temperature ionic liquid under the influence of irradiation

Radiation induced degradation effects are studied for a model ionic liquid (IL)--[EMIm]Tf(2)N--in order to distinguish in which way the results of X-ray based material analysis methods can be falsified by the radiation supplied by typical X-ray sources itself. Photoelectron spectroscopy is commonly used for determining the electronic structure of ionic liquids. Degradation effects, which often occur e.g. in organic materials during X-ray or electron irradiation, are potentially critical for the interpretation of data obtained from ionic liquids. The changes of the chemical composition as well as the radiation-induced desorption of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm]Tf(2)N) fragments are analysed by X-ray photoelectron spectroscopy (XPS) as well as quadrupole mass spectroscopy (QMS) upon exposure to monochromated or non-monochromated AlKα X-rays from typical laboratory sources. During the irradiation of [EMIm]Tf(2)N, an increasing carbon concentration is observed in both cases and especially the [Tf(2)N](-) ion is strongly altered. This observation is supported by the results from the QMS analysis which revealed a variety of different IL fragments that are desorbed during X-ray irradiation. It is shown that the decomposition rate is directly linked to the photon flux on the sample and hence has to be considered when planning an XPS experiment. However, for typical experiments on this particular IL the measurements suggest that the changes are on a larger time scale as typically required for spectra acquisition, in particular if monochromated X-ray sources are used.     

Development of Abraham model IL-specific correlations for N-triethyl(octyl)ammonium bis(fluorosulfonyl)imide and 1-butyl-3-methylpyrrolidinium bis(fluorosulfonyl)imide

ABSTRACT

Abraham model correlations are derived for describing gas-to-ionic liquid and water-to-ionic liquid partition coefficients from published experimental data for solutes dissolved in both N-triethyl(octyl)ammonium bis(fluorosulfonyl)imide and 1-butyl-3-methyl-pyrrolidinium bis(fluorosulfonyl)imide. Derived Abraham model correlations describe the observed partition coefficient data to within 0.13 log units. As part of the current study the existing equation coefficients for the N-triethyl(octyl)ammonium cation were updated and reported for the first time were equation coefficients for the bis(trifluorosulfonyl)imide anion.     

Functionalized 1,3-dialkylimidazolium bis(fluorosulfonyl)imide as neat ionic liquid electrolytes for lithium-ion batteries

Neat ionic liquid electrolytes based on functionalized 1,3-dialkylimidazolium cation and bis(fluorosulfonyl)imide anion were investigated in MCMB/LiFePO₄ full cells with commercial electrodes for the first time. Ether functionalization could bring the prominent improvement of initial efficiency and the comparable cycle performance to a conventional carbonate-based electrolyte. In view of full cells, it was inferred that the further oxidation on cathode of the reduction products on anode during the charge process might result in the serious capacity loss of initial cycle.     

Determination of ammonia based on the electro-oxidation of hydroquinone in dimethylformamide or in the room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

The results detail a novel methodology for the electrochemical determination of ammonia based on its interaction with hydroquinone in DMF. It has been shown that ammonia reversibly removes protons from the hydroquinone molecules, thus facilitating the oxidative process with the emergence of a new wave at less positive potentials. The analytical utility of the proposed methodology has been examined with a linear range from 10 to 95 ppm and corresponding limit-of-detection of 4.2 ppm achievable. Finally, the response of hydroquinone in the presence of ammonia has been examined in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide, [EMIM][N(Tf)₂]. Analogous voltammetric waveshapes to that observed in DMF were obtained, thereby confirming the viability of the method in either DMF or [EMIM][N(Tf)₂] as solvent.     

Effect of temperature and water content on the shear viscosity of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as studied by atomistic simulations

Atomistic simulations are conducted to examine the dependence of the viscosity of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide on temperature and water content. A nonequilibrium molecular dynamics procedure is utilized along with an established fixed charge force field. It is found that the simulations quantitatively capture the temperature dependence of the viscosity as well as the drop in viscosity that occurs with increasing water content. Using mixture viscosity models, we show that the relative drop in viscosity with water content is actually less than that that would be predicted for an ideal system. This finding is at odds with the popular notion that small amounts of water cause an unusually large drop in the viscosity of ionic liquids. The simulations suggest that, due to preferential association of water with anions and the formation of water clusters, the excess molar volume is negative. This means that dissolved water is actually less effective at lowering the viscosity of these mixtures when compared to a solute obeying ideal mixing behavior. The use of a nonequilibrium simulation technique enables diffusive behavior to be observed on the time scale of the simulations, and standard equilibrium molecular dynamics resulted in sub-diffusive behavior even over 2 ns of simulation time.     

Thermal decomposition mechanism of 1-ethyl-3-methylimidazolium bromide ionic liquid

In order to better understand the volatilization process for ionic liquids, the vapor evolved from heating the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIM(+)Br(-)) was analyzed via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and thermogravimetric analysis mass spectrometry (TGA-MS). For this ionic liquid, the experimental results indicate that vaporization takes place via the evolution of alkyl bromides and alkylimidazoles, presumably through alkyl abstraction via an S(N)2 type mechanism, and that vaporization of intact ion pairs or the formation of carbenes is negligible. Activation enthalpies for the formation of the methyl and ethyl bromides were evaluated experimentally, ΔH(?)(CH(3)Br) = 116.1 ± 6.6 kJ/mol and ΔH(?)(CH(3)CH(2)Br) = 122.9 ± 7.2 kJ/mol, and the results are found to be in agreement with calculated values for the S(N)2 reactions. Comparisons of product photoionization efficiency (PIE) curves with literature data are in good agreement, and ab initio thermodynamics calculations are presented as further evidence for the proposed thermal decomposition mechanism. Estimates for the enthalpy of vaporization of EMIM(+)Br(-) and, by comparison, 1-butyl-3-methylimidazolium bromide (BMIM(+)Br(-)) from molecular dynamics calculations and their gas phase enthalpies of formation obtained by G4 calculations yield estimates for the ionic liquids' enthalpies of formation in the liquid phase: ΔH(vap)(298 K) (EMIM(+)Br(-)) = 168 ± 20 kJ/mol, ΔH(f,?gas)(298 K) (EMIM(+)Br(-)) = 38.4 ± 10 kJ/mol, ΔH(f,?liq)(298 K) (EMIM(+)Br(-)) = -130 ± 22 kJ/mol, ΔH(f,?gas)(298 K) (BMIM(+)Br(-)) = -5.6 ± 10 kJ/mol, and ΔH(f,?liq)(298 K) (BMIM(+)Br(-)) = -180 ± 20 kJ/mol.     

Cathodic chloride extraction treatment of a late bronze-age artifact affected by bronze disease in room-temperature ionic-liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI)

This paper concentrates on a novel approach to the electrochemical treatment of bronze disease, based on the use of room-temperature ionic liquids (RTIL). In particular, we employed 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as the electrolyte for the galvanostatic cathodic treatment of a late bronze-age artifact that had been exposed to marine environment during its history, dating back to ca. 1100 B.C. After an accurate metallographic and structural analysis of the as-found object—proving, among other findings, that bronze disease is essentially related to the presence of nantokite locked inside subsurface pits of typical equivalent diameter of several hundred micrometers, we subjected it to optimal electrochemical conditions, showing—on the basis of X-ray diffraction—that nantokite could be effectively removed and Cu(I) reduced to metallic Cu. Numerical computations in the full three-dimensional pit geometry, with realistic nonlinear electrochemical boundary conditions, provide the theoretical framework for the choice of RTIL—as opposed to aqueous solutions—and for the quantitative evaluation of Cl⁻ removal rates.     

Cation-anion interactions in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-based ionic liquid electrolytes

An important step in developing ionic-liquid-based electrolytes for lithium rechargeable batteries is obtaining a molecular-level understanding of the ionic interactions that occur in these systems. In this study, 1-ethyl-3-methylimidazolium trifluoromethansulfonate ([C2mim]CF3SO3) is complexed with LiCF3SO3, and the local structures of the CF3SO3- and [C2mim]+ ions are investigated with infrared and Raman spectroscopy. The isolation and subsequent refinement of a Li[C2mim](CF3SO3)2 crystal provides further insight into the structure of the [C2mim]CF3SO3-LiCF3SO3 solutions. Minor changes are observed in the infrared and Raman spectra of dilute [C2mim]CF3SO3-LiCF3SO3 solutions compared to pure [C2mim]CF3SO3. However, a suspension of very small Li[C2mim](CF3SO3)2 crystallites forms at a solution composition of [C2mim]CF3SO3:LiCF3SO3 = 10:1 (mole ratio), placing an upper limit on the solubility of LiCF3SO3. Essentially no changes are observed in the vibrational modes of the [C2mim]+ cations over the entire range of LiCF3SO3 compositions studied, suggesting that the addition of these compounds does not significantly perturb the local structure of the [C2mim]+ cations. The salt used in this study has a common anion with the ionic liquid; thus, the ion cloud surrounding the [C2mim]+ ions, which must be primarily composed of CF3SO3- anions, is not significantly altered with the addition of LiCF3SO3.     

Nuclear magnetic relaxation and diffusion study of the ionic liquids 1-ethyl- and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide confined in porous glass

The molecular dynamics of the room-temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Bmim Tf2N) confined in porous glass is studied by nuclear magnetic resonance (NMR) relaxometry and diffusometry and is compared with the bulk dynamics over a wide temperature range. The molecular reorientation processes for anions and cations alike are found to be significantly affected by the presence of the glass interface at high temperatures. In this respect, the ionic liquid behaves similarly to polar liquids where proton NMR relaxation is governed by reorientations mediated by translational displacements (RMTDs). This process becomes less significant towards lower temperatures when the characteristic translational correlation times of the ions approach a timescale comparable with those of the RMTD process, and the relaxation dispersions in bulk and in confinement become similar below a temperature corresponding to about 1.2T_g, a value where the onset of dynamic heterogeneity has been observed before. The self-diffusion coefficient, on the other hand, is found to be strongly reduced than the bulk within the accessible temperature range of 248 K and above and is significantly slower than expected from the tortuosity effect, suggesting that ion–surface interactions affect the macroscopic properties.     

A molecular dynamics investigation of the structural and dynamic properties of the ionic liquid 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

Molecular dynamics simulations have been performed to investigate the structure and dynamics of the ionic liquid, 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C(4)mim][Tf(2)N]) in the temperature range of 283-460 K. Extensive analysis was carried out to characterize a number of structural and dynamic features. Transport properties were computed using a variety of equilibrium methods that employed the Green-Kubo and Einstein formulations. Nonequilibrium techniques were also used. In general, different methods mostly yielded consistent results, although some differences were observed. Computed self-diffusivities and ionic conductivities tended to be slightly lower than experimental values, while computed viscosities were significantly higher than experiment. Computed thermal conductivities agreed reasonably well with experimental data. Despite these discrepancies, the simulations capture the experimental temperature-dependent trends for all these transport properties. Single ion dynamics were studied by examining diffusional anisotropy, the self-part of the van Hove function, non-Gaussian parameters, and incoherent intermediate scattering functions. It is found that cations diffuse faster than anions and are more dynamically heterogeneous. A clear anisotropy is revealed in cation displacement, with the motion normal to the imidazolium ring plane being the most hindered and the motion along the alkyl chain in the plane of the ring being the most facile. Cations structurally relax faster than anions but they rotationally relax slower than anions. There is a pronounced temperature dependence to the rotational anisotropy of the cations, but only a weak temperature dependence for the anions. The ionic conductivity deviates from the Nernst-Einstein relation due to the correlated motion of cations and anions. The results suggest that the dynamical behavior of this and related ionic liquids is extremely complex and consists of many different modes with widely varying timescales, making the prediction of dynamical trends extremely difficult.