Pure IL Research Articles

Liquid Structure and Cluster Formation in Ionic Liquid/Water Mixtures – An Extensive ab initio Molecular Dynamics Study on 1-Ethyl-3-Methylimidazolium Acetate/Water Mixtures – Part

Abstract We present an extensive ab initio molecular dynamics study on mixtures of the room temperature ionic liquid 1-ethyl-3-methylimidazolium acetate with water. To show the dependence of the properties on the concentration, we simulated four different systems: Pure IL, pure water, and two binary mixtures with different mixing ratios. We found that the imidazolium rings are stacking on top of each other in the pure ionic liquid, which is a result of the strong dispersion interactions between the cations. With increasing water content, this ordering is disturbed. While in the pure IL the anions are located almost exclusively within the cation's ring plane, they occupy both the in-plane and the on-top position in the mixture. For very high water content, the anions are mainly found on top of the imidazolium ring. The ethyl chains of the cations attract each other via dispersion force and form clusters, indicating the existence of microheterogeneity in our simulations. We also analyzed the topology of the hydrogen bond network and found that the cation is forming hydrogen bonds to multiple anions at the same time, and is therefore a bridging agent. Likewise, the anion is bridging between different cations. At moderate water content, two acetate ions are frequently coordinated to the same water molecule, leading to the formation of acetate/water clusters.

Thermal Stability, Complexing Behavior, and Ionic Transport of Polymeric Gel Membranes Based on Polymer PVdF-HFP and Ionic Liquid, [BMIM][BF4

PVdF-HFP + IL(1-butyl-3-methylimidazolium tetrafluoroborate; [BMIM][BF(4)]) polymeric gel membranes containing different amounts of ionic liquid have been synthesized and characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR), differential scanning calorimetry, thermogravimetric analysis (TGA), and complex impedance spectroscopic techniques. Incorporation of IL in PVdF-HFP polymer changes different physicochemical properties such as melting temperature (T(m)), thermal stability, structural morphology, amorphicity, and ionic transport. It is shown by FTIR, TGA (also first derivative of TGA, "DTGA") that IL partly complexes with the polymer PVdF-HFP and partly remains dispersed in the matrix. The ionic conductivity of polymeric gel membranes has been found to increase with increasing concentration of IL and attains a maximum value of 1.6 × 10(-2) S·cm(-1) for polymer gel membrane containing 90 wt % IL at room temperature. Interestingly, the values of conductivity of membranes with 80 and 90 wt % of IL were higher than that of pure IL (100 wt %). The polymer chain breathing model has been suggested to explain it. The variation of ionic conductivity with temperature of these gel polymeric membranes follows Arrhenius type thermally activated behavior.

Synthesis and Physicochemical Properties of Amino Acid Ionic Liquid 1-Butyl-3-methylimidazolium Aspartate and Binary Mixture with Methanol

An amino acid based ionic liquid [Bmim][Asp], 1-butyl-3-methylimidazolium aspartate, and a binary mixture system composed of [Bmim][Asp] and methanol were synthesized and prepared, respectively. The density, surface tension, and electrical conductivity of the pure IL and the binary system were measured or estimated by the extrapolation method at different temperatures. The physicochemical properties of the IL or the binary system like the molecular volume, standard molar entropy, lattice energy, parachor, speed of sound, molar enthalpy of vaporization, interstice volume, thermal expansion coefficient, excess volume, and so forth were estimated by empirical and semiempirical equations. The glass transition temperature was determined by the differential scanning calorimetry (DSC). The status of intermolecular interaction based on the excess volume change of the IL mixture was discussed at 298.15 K. By Vogel–Fulcher–Tamman (VFT) and Castell–Amis (CA) equations, the relationship between the electrical conduct...

Measurements, Correlations, and Predictions of Thermodynamic Properties of N-Octylisoquinolinium Thiocyanate Ionic Liquid and Its Aqueous Solutions

N-Octylisoquinolinium thiocyanate, [C8iQuin][SCN], has been synthesized in our laboratory from [C8iQuin][Br] as a substrate. The compound was characterized using 1H-NMR, 13C-NMR, and elemental analysis. Karl Fisher titration was used to determine the water content. The density and viscosity of pure ionic liquid were determined over a wide temperature range from (288.15 to 348.15) K. The basic thermal properties of the pure IL have been measured using by means of a differential scanning microcalorimetry technique (DSC). Decomposition of the IL was detected by the simultaneous TG/DTA experiments. (Liquid + liquid) phase equilibria (LLE) have been measured for binary mixtures {[C8iQuin][SCN] (1) + water (2)} using a dynamic method at atmospheric pressure. The experiments have been done over a broad range of ionic liquid mole fraction, x1, and temperatures from 250 K to the boiling point of water. Experimental heat capacities and excess enthalpies were determined for {[C8iQuin][SCN] (1) + water (2)} binary mixtures for different IL mole fractions at a wide range of the temperature at ambient pressure. The influence of temperature and composition was assessed, and suitable equations were used to correlate the experimental data. The experimental results were compared with data for other ionic liquids available in the open literature.

Fluorescence of nanocomposite materials with hydroxyl-functionalised ionic liquid confined into mesoporous silica gel

Nanocomposite materials (IL-sg) of hydroxyl-functionalised ionic liquid 1-hydroxyethyl-3-methlyimidazolium dicyanamide EOHMImN(CN)2 physically confined into mesoporous silica gel are synthesised according to a proper sol-gel process. The silica gel has disordered wormhole-like pore structure and average pore diameter of 3.3–6.2 nm. The materials exhibit notably enhanced fluorescence emissions compared with pure IL. The hydroxyl group on the cation of IL has an obvious effect on the fluorescence emissions of pure IL and the materials, i.e. the emission intensity of pure EOHMImN(CN)2 is c.a. 1.8 times stronger than that of pure IL 1-ethyl-3-methlyimidazolium dicyanamide EMImN(CN)2, however, the emission intensity of EOHMImN(CN)2-sg is c.a. two times weaker than that of EMImN(CN)2-sg.

Generalized PSRK Model for Prediction of Liquid Density of Ionic Liquids

Abstract A simple and generalised expression for adjustable parameter for pure ionic liquids in conjunction with predictive-Soave- Redlich-Kwong (PSRK) approach is presented for prediction of pure IL density. The proposed expression is based on the correlation developed by Nasrifar and Moshfeghian for perfection of saturated liquid density for pure compounds. The generalized expression uses acentric factor and mass connectivity index of pure ionic liquids. A set of 47 pure ionic liquids with 735 data points and 4 different cohesion functions were used in the study. The results were compared with linear generalized model (LGM) developed by Valderrama to check appropriateness and accuracy of expression presented. It was found that the compound specific PSRK approach gives very accurate predictions and generalized expression is at par with LGM model. Further study would include use of other cohesion factor models.

LiFePO4/Li Batteries with Mixtures of Carbonate and Ionic Liquid [EMIM]+[TFSI]- as High Properties and Safety Electrolyte

The electrolyte optimum composition consists of 1mol/L LiTFSI in the [EMIM]+[TFSI]-mixed with EC and DMC in weight ratio of 60:20:20. The LiFePO4/Li cell using 1 mol/L LiTFSI/([EMIM]+[TFSI]-/EC/DMC) as electrolyte show that the first coulomb efficiency was 90% and the first discharge capacity was 168mAh g-1. The 15th reversible capacities were maintain 157mAh g-1at 0.2C. Compared with traditional organic electrolyte and pure IL electrolyte, IL-based mixed electrolyte have good coulomb efficiencies and higher charge and discharge performances. The lithium transference number of IL-based mixed electrolyte at room temperature are 0.59. Thermal stability of IL-based mixed electrolyte higher than traditional organic electrolyte, and show almost non-flammability by the burning tests.

Ionogels based on ionic liquids as potential highly conductive solid state electrolytes

The preparation and properties of ionogels as potential highly conductive solid state electrolytes has been investigated. The ionogels have been prepared by a one-pot sol–gel synthesis using tetraethoxysilane (TEOS) in an ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIm][BF4]. The effect of silica content in the ionogels was characterized and analyzed in terms of chemical interactions, thermal stability and ionic conductivity. Immobilization of the IL in the silica network was observed even at high loading of IL (97wt.%). Hydrogen bond networks between BF4− and the hydroxyl group in the silica was suggested as the mechanism of this immobilization, which was characterized by FTIR and solid-state NMR. TGA analysis shows that the prepared ionogels were stable up to around 450°C, where a-final one-step degradation occurs. The ionic conductivity was found to decrease as the amount of silica increased. However, with high loading of IL (97wt.%) the ionic conductivity was close to that of the pure IL. From the results obtained, these ionogels can be considered potential candidates for electrochemical devices where high ionic conductivity in solid state materials is desirable.

Phase Equilibria Study of the Binary Systems (N-Hexylisoquinolinium Thiocyanate Ionic Liquid + Organic Solvent or Water)

Liquid-liquid phase equilibria (LLE) of binary mixtures containing a room-temperature ionic liquid N-hexylisoquinolinium thiocyanate, [HiQuin][SCN] with an aliphatic hydrocarbon (n-hexane, n-heptane), aromatic hydrocarbon (benzene, toluene, ethylbenzene, n-propylbenzene), cyclohexane, thiophene, water, and 1-alcohol (1-ethanol, 1-butanol, 1-hexanol, 1-octanol, 1-decanol) have been determined using a dynamic method from room temperature to the boiling-point of the solvent at ambient pressure. N-hexylisoquinolinium thiocyanate, [HiQuin][SCN] has been synthesized from N-hexyl-isoquinolinium bromide as a substrate. Specific basic characterization of the new compound including NMR spectra, elementary analysis, and water content have been done. The density and viscosity of pure ionic liquid were determined over a wide temperature range from 298.15 to 348.15 K. The mutual immiscibility with an upper critical solution temperature (UCST) for the binary systems {IL + aliphatic hydrocarbon, cyclohexane, or water} was detected. In the systems of {IL + aromatic hydrocarbon or thiophene} an immiscibility gap with a lower critical solution temperature (LCST) was observed. Complete miscibility in the liquid phase, over a whole range of ionic liquid mole fraction, was observed for the binary mixtures containing IL and an 1-alcohol. For the tested binary systems with immiscibility gap {IL + aliphatic hydrocarbon, aromatic hydrocarbon, cyclohexane, thiophene, or water}, the parameters of the LLE correlation have been derived using the NRTL equation. The basic thermal properties of the pure IL, that is, the glass-transition temperature as well as the heat capacity at the glass-transition temperature, have been measured using a differential scanning microcalorimetry technique (DSC). Decomposition of the IL was detected by simultaneous thermogravimetric/differential thermal analysis (TG/DTA) experiments.

Mixtures of ionic liquids for low temperature electrolytes

The conductivity, viscosity and the self-diffusion coefficient of pyrrolidinium-based ILs (ILs), N-butyl-N-methyl pyrrolidinium-bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) and N-methyl-N-propyl pyrrolidinium-bis(fluorosulfonyl)imide (Pyr13FSI), and their binary mixtures were investigated in order to better understand their behavior as electrolyte components in supercapacitor and lithium battery systems. The IL mixtures showed excellent low temperature properties far exceeding those of the pure IL materials. For example, at −40°C the conductivity of binary mixtures was found to be up to four orders of magnitude higher than that of the pure ILs.

Vesicles in Ionic Liquids

The formation of vesicles from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) in several room-temperature ionic liquids, namely, 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF(4)), 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf(2)), and N-benzylpyridinium bis(trifluoromethylsulfonyl)imide (BnPyNTf(2)), as well as in a water/BmimBF(4) mixture, was investigated. In pure ionic liquids, observations by staining transmission electron microscopy demonstrated clearly the formation of spherical structures with diameters of 200-400 nm. The morphological characteristics of these vesicles in ionic liquids, in particular, the membrane thicknesses, were first investigated by small-angle neutron scattering measurements. The mean bilayer thickness was found to be ∼63 ± 1 Å in a deuterated ionic liquid (BnPyNTf(2)-d). This value was similar to that observed in water. The effect of ILs on the modification of the phase physical properties of multilamellar vesicles (MLVs) was then investigated by differential scanning calorimetry. In pure IL as in water, DPPC exhibited an endothermic pretransition followed by the main transition. These transition temperatures and the associated enthalpies in ILs were higher than those in water because of a reduction of the electrostatic repulsion between zwitterionic head groups. To better understand the effect of ionic liquid on the formation of multilamellar vesicles, mixtures of BmimBF(4) and water, which are miscible in all proportions, were analyzed (BmimBF(4)/water ratio from 0% to 100%). SANS and DSC experiments demonstrated that the bilayer structure and stability were strongly modified by the IL content. Moreover, matching SANS experiments showed that BmimBF(4) molecules prefer to be located inside the DPPC membrane rather than in water.

Density and viscosity of 1-butyl-3-methylimidazolium nitrate with ethanol, 1-propanol, or 1-butanol at several temperatures

Densities and viscosities of 1-butyl-3-methylimidazolium nitrate [Bmim][NO 3], and its binaries with alcohol (ethanol, 1-propanol, or 1-butanol) were measured at different temperatures. The densities and viscosities of pure ionic liquid were correlated successfully by empirical equations. The Vogel–Fulcher–Tammann equations can fit the experimental data of viscosities for pure IL. Excess molar volume and viscosity deviations were calculated for the binaries. The excess molar volumes have negative deviations from the ideal solution.

Electrochemical and Physicochemical Properties of PYR14-FSI Based Electrolytes with LiFSI

N-methyl-N-butylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid (PY14FSI)-based electrolytes with LiFSI have been characterized in terms of conductivity, viscosity, thermal phase behavior, electrochemical and thermal stability. The results indicate a high conductivity for the pure ionic liquid and those containing LiFSI. The addition of salt lowers the melting temperature of the electrolyte mixture and, for some of the electrolytes, the conductivity is superior to 10-5 S cm-1 at -40{degree sign}C and up to 3.7 mS cm-1 at 25{degree sign}C. For the more conductive electrolyte at room temperature ((1-x) PY14FSI-(x) LiFSI (x = 0.10)), lithium metal has been cycled for more than 200 cycles at 20{degree sign}C with little overpotential relative to the Li0/Li+ couple, showing that the passivation layer on the surface of lithium is stable and allows reversible lithium deposition. One drawback of these electrolytes is the low thermal degradation temperature, which is lower than that of the pure IL, which may be attributed to impurities in the commercially available LiFSI.

Electrochemical behavior of K4Fe(CN)6 in [bmim]PF6/TX-100/H2O based microemulsions

The electrochemical behavior of potassium ferrocyanide [K4Fe(CN)6] at Pt/ionic liquid (IL) microemulsion interfaces was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). H2O/TX-100/bmimPF6 was used to prepare three IL microemulsions: water in 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) (W/IL), bicontinuous (WIL) and bmimPF6 in water (IL/W). The results show that the IL microemulsion systems have relatively narrower potential windows compared with the pure IL system. The redox potential gap is about 100 mV in the pure water and the three IL microemulsions. The redox potentials of K4Fe(CN)6/K3Fe(CN)6 and the redox peak currents decrease in the order pure water, IL/W, WIL, W/IL. Furthermore, the peak currents increase linearly with the square root of the scan rate, while the diffusion coefficient increased in the order W/IL, WIL, IL/W. The Nyquist plots obtained in the WIL and IL/W systems show capacitive resistance arcs at high frequencies and 45° straight lines at low frequencies, implying that the electrochemical reactions are controlled by charge transfer and diffusion steps. For the W/IL system there is only a 45° straight line in the Nyquist plot, indicating that diffusion is the controlling step at all frequencies.

Solvatochromic parameters for binary mixtures of an ionic liquid with various protic molecular solvents

Solvatochromic parameters (E N , normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous solution, E N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute–solvent and solvent–solvent interactions were applied to interpret the results. Predicted values of solvatochromic parameters (SP) (E N , normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) from the correlation equations versus its experimental values for binary mixtures of 2-hydroxyethylammonium formate with water, methanol, ethanol, propan-1-ol and propan-2-ol.

Ionic liquid microemulsions: A new medium for electropolymerization

The direct anodic oxidation electropolymerization of 3,4-ethylenedioxythiophene (EDOT) in IL microemulsions, BmimPF 6/Tween 20/H 2O, has been investigated for the first time. Electrochemical measurements indicated that among water-in-BmimPF 6 (W/IL), bicontinuous (B.C.), and BmimPF 6-in-water (IL/W) sub-regions in BmimPF 6/Tween 20/H 2O system, IL/W was the most suitable for the electropolymerization of EDOT, while the electropolymerization did not happen in W/IL. The use of IL microemulsions remarkably reduces the amount of IL, especially for IL/W. UV–vis spectra confirmed the formation of PEDOT. Scanning electron microscopy results demonstrated that nanostructures of compact PEDOT films were still obtained as in pure IL, implying their possible utilization in ion-selective electrodes, ion-sieving films, and matrices for hosting catalyst particles.

Enthalpy of Solution of Amino Acid Ionic Liquid 1-Ethyl-3-methylimidazolium Ammonioacetate

The molar enthalpies of solution, ΔsolHm(wc), of 1-ethyl-3-methylimidazolium ammonioacetate (EMIGly) with various amounts of water and with various molalities were measured by the solution−reaction isoperibol calorimeter at (298.15 ± 0.01) K. According to Archer’s method, the standard molar enthalpis of solution of EMIGly with a known amount of water, ΔsolH0m(wc), were obtained. In order to eliminate the effect of the small amount of water in EMIGly, a linear fitting of ΔsolH0m(wc) against water content was carried out so that a good straight line was obtained, and the intercept was the standard molar enthalpy of solution, ΔsolH0m (pure IL EMIGly) = (−34.6 ± 0.5) kJ·mol−1. Using Glasser’s theory of lattice energy, the hydration enthalpy of the anion of glycine was estimated.

Reduced production of hyperalgesic substances by mononuclear cells from aged rats incubated with carrageenan: role of interleukin 2 and prostaglandins.

To compare the production of hyperalgesic substances by cells from aged (A; 24-month) and juvenile (J; 2-month) rats. 4 x 10(5) purified mononuclear cells from J and A were 2 h-stimulated (test) or not (control) by 250 microg lambda-carrageenan/well. Supernatants (0.1 ml) were intraplantarly (ipl) injected in rat paws and development of mechanical hyperalgesia, in grams, evaluated. Rat interleukin 2 (IL 2) and prostaglandin E2 (PGE2) were also assessed for hyperalgesia development. Test supernatants from A compared with J induced significantly less hyperalgesia (-56 +/- 8.1 and -88.4 +/- 4.6 g, respectively, p < 0.05, ANOVA t test). Local injection of a specific, but not a control, antiserum against IL 2 significantly blocked both pure IL 2- and stimulated supernatants-derived hyperalgesia. In contrast to PGE-like materials, IL 2 content in supernatants was compatible with hyperalgesia development. Hyperalgesia induced by test supernatants was significantly less intense when derived from aged animals. IL 2 may have accounted for such hyperalgesia.

Stable expression of clonal specificity in murine cytomegalovirus-specific large granular lymphoblast lines propagated long-term in recombinant interleukin 2

The somatic stability of cloned long-term cytolytic T lymphocyte lines (CTLL) specific for antigens encoded by murine cytomegalovirus (MCMV) was tracked for more than two years of continuous in vitro propagation. Clone S1 retained its original specificity for a structural (S) antigen of MCMV for about eight months in the presence of antigen and interleukin 2 (IL 2), but not in IL 2 alone. In the following months, however, in spite of the continued presence of antigen, clonal variants developed that displayed distinct patterns of target cell recognition, including loss of the original specificity and acquisition of exclusive specificity for the natural killer target cell YAC-1. On the other hand, large granular lymphoblast (LGL) lines, line IE1IL and a series of sublines thereof, could be established that stably expressed L d-restricted specificity for a viral nonstructural immediate-early (IE) antigen more than two years after withdrawal of antigen and feeder cells when propagated in the presence of pure recombinant human IL 2. The finding that the presence of antigen was not essential for the stability of clone IE1-derived CTLL indicates that maintenance of specificity in LGL lines is not a result of antigen-mediated selection, but reflects an intrinsic property.

Mitogenic effect of PMA + IL 2 on subpopulations of corticoresistant thymocytes.

The proliferative response of subpopulations of corticoresistant thymocytes (CRT) to phorbol-12-myristate-13-acetate (PMA) + interleukin 2 (IL 2) was investigated. Thymocyte subpopulations were selected by the indirect "panning" technique, and their purity was checked by cytofluorometry. Microcultures were set up with an optimal concentration of PMA, EL4 supernatant, or pure IL 2 obtained by recombinant DNA technology (r-IL 2) in the presence or in the absence of accessory splenic adherent cells (SAC). Under these conditions, only the Lyt-2+ CRT proliferated, and this response was IL 2-dose-dependent and was increased by accessory cells. When the calcium ionophore A23187 was added to the cultures, the proliferation of L3T4+ CRT was greatly increased. These results were confirmed by cultures at limiting dilution of positively selected Lyt-2+ and L3T4+ subpopulations of CRT at optimal concentrations of PMA, r-IL 2, A23187, and accessory cells. These results are consistent with the idea that two signals are necessary to activate L3T4+ CRT, whereas only IL 2 is necessary for PMA-induced proliferation of Lyt-2+ CRT. Finally, unlike the case of lectin-induced proliferation of Lyt-2+ and L3T4+ CRT, the presence of accessory cells or cell-cell contact is important for optimal response to PMA + IL 2.