Molecular dynamics simulation of the ionic liquid N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide

Thermodynamics, structure, and dynamics of an ionic liquid based on a quaternary ammonium salt with ether side chain, namely, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, MOENM2E TFSI, are investigated by molecular dynamics (MD) simulations. Average density and configurational energy of simulated MOENM2E TFSI are interpreted with models that take into account empirical ionic volumes. A throughout comparison of the equilibrium structure of MOENM2E TFSI with previous results for the more common ionic liquids based on imidazolium cations is provided. Several time correlation functions are used to reveal the microscopic dynamics of MOENM2E TFSI. Structural relaxation is discussed by the calculation of simultaneous space-time correlation functions. Temperature effects on transport coefficients (diffusion, conductivity, and viscosity) are investigated. The ratio between the actual conductivity and the estimate from ionic diffusion by the Nernst-Einstein equation indicates that correlated motion of neighboring ions in MOENM2E TFSI is similar to imidazolium ionic liquids. In line with experiment, Walden plot of conductivity and viscosity indicates that simulated MOENM2E TFSI should be classified as a poor ionic liquid.     

A new fluorinated anion for room-temperature ionic liquids

A new room-temperature ionic liquid (RTIL) consisting of the fluorinated anion bis(trifluoromethyl)-phosphinate((CF₃)₂PO₂⁻) coupled with the 1-butyl-3-methyl-imidazoliuim (BMIM) cation has been synthesized and characterized by physicochemical and electrochemical means including differential scanning calorimetry (DSC), thermogravimetric analysis, viscosity, conductivity and cyclic voltammetry measurements. Properties are compared with those of the known RTIL consisting of BMIM coupled with the bis(trifluoromethyl)-sulfonylimide (TFSI) anion.     

Effect of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide on the properties of poly(glycidyl methacrylate) based solid polymer electrolytes

A free standing polymer electrolytes films, containing poly(glycidyl methacrylate) (PGMA) as the polymer host, lithium perchlorate (LiClO₄), and ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide [Bmim][TFSI] as a plasticizer was successfully prepared via the solution casting method. The XRD analysis revealed the amorphous nature of the electrolyte. ATR-FTIR and thermal studies confirmed the interaction and complexation between the polymer host and the ionic liquid. The maximum ionic conductivity of the solid polymer electrolyte was found at 2.56 × 10^–5 S cm^–1 by the addition of 60 wt % [Bmim][TFSI] at room temperature and increased up to 3.19 × 10^–4 S cm^–1 at 373 K, as well as exhibited a transition of temperature dependence of conductivity: Arrhenius-like behavior at low and high temperatures.     

Low-viscosity and low-melting point asymmetric trialkylsulfonium based ionic liquids as potential electrolytes

Nine new ionic liquids based on small asymmetric trialkylsulfonium cations with TFSI⁻ anion were prepared and characterized. Physical and electrochemical properties of these ionic liquids, including melting point, thermal stability, viscosity, conductivity and electrochemical window were determined. Reducing symmetry of cations reduces the melting points of these ILs. Some of these hydrophobic ionic liquids showed low-viscosity and low-melting point characteristics. The viscosities of S₂₂₃TFSI, S₂₂₁TFSI and S₁₂₃TFSI were 33, 36 and 39 mPa s at 25 °C, respectively. Electrochemical and thermal stabilities of these ILs permitted them to become promising electrolytes used in electrochemical devices.     

On the interaction of carbon electrodes and non conventional electrolytes in high-voltage electrochemical capacitors

This study is essentially based on innovative electrolytes such as the organic salt N-methyl-N-butylpyrrolidinium tetrafluoroborate (Pyr₁₄BF₄) dissolved in propylene carbonate (PC) and the pure ionic liquid (N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI) and its solution in PC. Activated carbon cloths were used as self-standing binder-free electrodes. It is found that the presence of impurities in carbon electrodes may lead to electrolyte decomposition and electrode degradation which notably affect the electrochemical double-layer capacitor (EDLC) performance. Such processes greatly depend on the composition of both the electrode and the electrolyte, being much less significant with solvent-containing electrolytes. By raising the operation temperature to 60 °C, the EDLC performance in the ionic liquid Pyr₁₄TFSI is notably improved due to a relevant decrease in the viscosity and increase in ionic conductivity. By contrast, the presence of impurities, e.g., Zn and Al, in the electrodes remarkably reduces the electrolyte stability and a thick layer of decomposition products completely covers the carbon fibers after cycling at high temperature. The ionic liquid in solution maintains the high maximum operative voltage of the net ionic liquid whereas its viscosity and ionic conductivity are close to those of the conventional Et₄NBF₄/PC. Furthermore, the presence of propylene carbonate as solvent prevents to some extent the ionic liquid degradation.     

A mild, efficient, and selective deprotection of tert-butyldimethylsilyl (TBDMS) ethers using dicationic ionic liquid as a catalyst

Selective deprotection of alkyl TBDMS ether in the presence of phenolic TBDMS ether using dicationic ionic liquid [tetraEG(mim)₂][OMs]₂ as a homogeneous catalyst showed significant catalytic activity in methanol at ambient temperature to produce respective alcohol in excellent yield. The present environmentally benign catalytic system is found to be very convenient, fast, high yielding, and clean method for selective desilylation of alkyl silyl ethers even in the existence of other sensitive organic functional groups such as aldehyde, methoxy, and acetate were also achieved.     

Modification of carbon electrode in ionic liquid through the reduction of phenyl diazonium salt. Electrochemical evidence in ionic liquid

Electrochemical reduction of the 4-nitrophenyl diazonium salt in ionic liquid media has been investigated at carbon electrode. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The cyclic voltammetry study demonstrated the possibility of the electrochemical grafting of the nitrophenyl groups onto carbon electrode after the reduction of its corresponding diazonium in ionic liquid. The electrochemical characterization of the modified electrode achieved on ionic liquid displays the presence of the nitrophenyl group at the carbon surface. Moreover, the surface concentration of the attached group obtained in this media was found to be around 1.7 × 10⁻¹⁰ mol cm⁻², this value may suggest the possibility of the formation of monolayer. Furthermore, the characterization of the modified electrode in [EMIM][TFSI] showed the conversion of some NO₂-phenyl groups to NHOH-phenyl. This observation could indicate the presence of surface interaction between the reduced NO₂-phenyl and the ionic liquid cation, thanks to the presence of acidic proton in the ionic liquid cation.     

Application of novel room temperature ionic liquids in flexible supercapacitors

This paper studied application of different types of room temperature ionic liquids (RTILs) into flexible supercapacitors. Typical RTILs including 1-buthyl-3-methyl-imidazolium [BMIM][Cl], trioctylmethylammonium bis(trifluoromethylsulfonyl)imide [OMA][TFSI] and triethylsulfonium bis(trifluoromethylsulfonyl)imide ([SET₃][TFSI]) were studied. [SET₃][TFSI] shows the best result as electrolyte in electrochemical double-layer (EDLC) supercapacitors with very high specific capacitance of 244 F/g at room temperature, overceiling the performance of conventional carbonate electrolyte such as dimethyl carbonate (DMC) with more stable performance and much larger electrochemical window.     

Transport coefficients, Raman spectroscopy, and computer simulation of lithium salt solutions in an ionic liquid

Lithium salt solutions of Li(CF3SO2)2N, LiTFSI, in a room-temperature ionic liquid (RTIL), 1-butyl-2,3-dimethyl-imidazolium cation, BMMI, and the (CF3SO2)2N(-), bis(trifluoromethanesulfonyl)imide anion, [BMMI][TFSI], were prepared in different concentrations. Thermal properties, density, viscosity, ionic conductivity, and self-diffusion coefficients were determined at different temperatures for pure [BMMI][TFSI] and the lithium solutions. Raman spectroscopy measurements and computer simulations were also carried out in order to understand the microscopic origin of the observed changes in transport coefficients. Slopes of Walden plots for conductivity and fluidity, and the ratio between the actual conductivity and the Nernst-Einstein estimate for conductivity, decrease with increasing LiTFSI content. All of these studies indicated the formation of aggregates of different chemical nature, as it is corroborated by the Raman spectra. In addition, molecular dynamics (MD) simulations showed that the coordination of Li+ by oxygen atoms of TFSI anions changes with Li+ concentration producing a remarkable change of the RTIL structure with a concomitant reduction of diffusion coefficients of all species in the solutions.     

A novel ternary polymer electrolyte for LMP batteries based on thermal cross-linked poly(urethane acrylate) in presence of a lithium salt and an ionic liquid

A new ternary polymer electrolyte based on thermally cross-linked poly(urethane acrylate) (PUA), lithium bis(trifluoromethansulfonyl)imide (LiTFSI) and the ionic liquid N-butyl-N-methylpyrrolidinium TFSI (PYR₁₄TFSI) was developed and tested for application in LMP batteries. The polymer electrolyte was a transparent yellow self-standing material with quite good mechanical properties, i.e., comparable to that of a flexible rubber. The room temperature ionic conductivity of the dry polymer electrolyte was found to be as high as 0.1 mS cm⁻¹ for the compound containing 40 wt% of ionic liquid (PYR₁₄TFSI) and a O/Li ratio of 15/1 (Li⁺ from LiTFSI). The thermal analysis of the new cross-linked electrolyte showed that it was homogeneous, amorphous and stable over a wide temperature range extending from −40 °C to 100 °C. The homogeneity of the polymer electrolyte was also confirmed by SEM analysis.     

Acrylate functionalized tetraalkylammonium salts with ionic liquid properties

Acrylate functionalized ionic liquids based on tetraalkylammonium salts with terminal acrylates- and methylacrylates were synthesized. Melting points and ionic conductivity of twenty compounds in six groups were determined. Within one group the effect of three different counterions was investigated and discussed. The groups differ in cationic structure elements because of their functional groups such as acrylate and methacrylate, alkyl residues at the nitrogen and number of quaternary ammonium atoms within the organic cation. The effect of these cationic structure elements has been examined concerning the compiled parameters with a view to qualifying them as components for solid state electrolytes. The newly synthesized ionic liquids were characterized by NMR and FTIR analysis. The exchange of halide ions like bromide as counter ions to weakly coordinating [PF?]?, [OTf]? or [TFSI]? reduces the melting points significantly and leads to an ion conductivity of about 10?? S/cm at room temperature. In the case of the dicationic ionic liquid, an ion conductivity of about 10?3 S/cm was observed.     

Synthesis,crystal structure and photochromic property of a phenethyl viologen bismuth(III) chloride

Viologen bismuthate halides generally show photochromic properties. In the present work, phenylethyl alcohol was introduced into chloro bismuthates in the hope to prepare photochromic crystalline materials and finally a photochromic inorganic-organic hybrid, (PeV)₃(Bi₂Cl₉)₂ (1), based on an in situ generated PeV²⁺ cation (PeV²⁺ = phenethylviologen = N,N′-diphenethyl-4,4′-bipyridinium), has been obtained, whose microstructure contains a discrete dimer [Bi₂Cl₉]^3– counterion identified by single crystal X-ray diffraction. More importantly, 1 exhibits a typical photochromic behavior, which can be mainly attributed to the reversible inter-conversion between the monocation viologen radical [PeV]^+? and the viologen dication [PeV]²⁺.     

Coordination polymer glass from a protic ionic liquid: proton conductivity and mechanical properties as an electrolyte

High proton conducting electrolytes with mechanical moldability are a key material for energy devices. We propose an approach for creating a coordination polymer (CP) glass from a protic ionic liquid for a solid-state anhydrous proton conductor. A protic ionic liquid (dema)(H₂PO₄), with components which also act as bridging ligands, was applied to construct a CP glass (dema)_0.35[Zn(H₂PO₄)_2.35(H₃PO₄)_0.65]. The structural analysis revealed that large Zn–H₂PO₄⁻/H₃PO₄ coordination networks formed in the CP glass. The network formation results in enhancement of the properties of proton conductivity and viscoelasticity. High anhydrous proton conductivity (σ = 13.3 mS cm⁻¹ at 120 °C) and a high transport number of the proton (0.94) were achieved by the coordination networks. A fuel cell with this CP glass membrane exhibits a high open-circuit voltage and power density (0.15 W cm⁻²) under dry conditions at 120 °C due to the conducting properties and mechanical properties of the CP glass.

A proton-conducting coordination polymer glass derived from a protic ionic liquid works as a moldable solid electrolyte and the anhydrous fuel cell showed I–V performance of 0.15 W cm⁻² at 120 °C.     

Quantum design of ionic liquids for extreme chemical inertness and a new theory of the glass transition

In many modern technologies (such as batteries and supercapacitors), there is a strong need for redox-stable ionic liquids. Experimentally, the stability of ionic liquids can be quantified by the voltage range over which electron tunneling does not occur, but so far, quantum theory has not been applied systematically to this problem. Here, we report the electrochemical reduction of a series of quaternary ammonium cations in the presence of bis(trifluoromethylsulfonyl)imide (TFSI) anions and use nonadiabatic electron transfer theory to explicate the results. We find that increasing the chain length of the alkyl groups confers improved chemical inertness at all accessible temperatures. Simultaneously, decreasing the symmetry of the quaternary ammonium cations lowers the melting points of the corresponding ionic liquids, in two cases yielding highly inert solvents at room temperature. These are called hexyltriethylammonium TFSI (HTE-TFSI) and butyltrimethylammonium TFSI (BTM-TFSI). Indeed, the latter are two of the most redox-stable solvents in the history of electrochemistry. To gain insight into their properties, very high precision electrical conductivity measurements have been carried out in the range +20 °C to +190 °C. In both cases, the data conform to the Vogel-Tammann-Fulcher (VTF) equation with “six nines” precision (R ²?>?0.999999). The critical temperature for the onset of conductivity coincides with the glass transition temperature T _g. This is compelling evidence that ionic liquids are, in fact, softened glasses. Finally, by focusing on the previously unsuspected connection between the molecular degrees of freedom of ionic liquids and their bulk conductivities, we are able to propose a new theory of the glass transition. This should have utility far beyond ionic liquids, in areas as diverse as glassy metals and polymer science.     

Physicochemical properties of ionic liquid analogue containing magnesium chloride as temperature and composition dependence

The ionic liquid analogue containing MgCl₂ based on choline chloride and glycerol was reported. The solubility of MgCl₂ in the ionic liquid analogue based on choline chloride and glycerol was measured from T?=?293?C393?K. The empirical equation about the solubility and temperature was obtained. Thermal analysis showed that the ionic liquid analogue was stable from room temperature to 140?°C. The physical properties such as conductivity ??, density ?? and viscosity ?? of ionic liquid analogue were measured as function of the content of MgCl₂ and temperature. An empirical equation about the density (??) and temperature was obtained. The ions transport behaviours are analyzed using hole-theory. It is shown that the conductivity of the ionic liquid analogues is controlled by the ion mobility and the suitable voids.     

Novel functionalized ionic liquid with a sulfur atom in the aliphatic side chain of the pyrrolidinium cation

A novel ionic liquid, never reported in literature until now, was properly designed, synthesized and preliminary investigated. This material was prepared combining the N-methylpyrrolidinium cation (PYR_1(2S1))⁺, exhibiting a sulfur atom in the alkyl side chain, with the bis(trifluoromethanesulfonyl)imide anion, (TFSI)⁻, to be addressed as safer electrolyte component for sulfur-based battery systems. The presence of sulfur within the cation side chain was found to prevent the crystallization of the ionic liquid even in the presence of lithium salt. Cyclic voltammetries have clearly indicated that Li⁺ cation exhibits good mobility and is reversibly plated/stripped in PYR_1(2S1)TFSI–LiTFSI electrolytes with high efficiency.     

Main‐chain viologen polymers with organic counterions exhibiting thermotropic liquid‐crystalline and fluorescent properties*

A series of viologen polymers with bromide, tosylate, and triflimide as counterions were prepared by either the Menshutkin reaction or metathesis reaction in a common organic solvent. Their polyelectrolyte behavior in methanol was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid‐crystalline properties with a number of experimental techniques. Each of the viologen polymers with organic counterions had a low melting transition or fusion temperature above which it formed either a high‐order smectic phase or a low‐order smectic phase. Each of them also exhibited a smectic‐to‐isotropic transition. The ranges of the liquid‐crystalline phase were 80–88 °C for viologen polymers with tosylate as a counterion and 120–146 °C for viologen polymers with triflimide as a counterion. They had excellent thermal stability. The ranges of thermal stability were 288–329 °C for viologen polymers with tosylate as a counterion and 343–350 °C for viologen polymers with triflimide as a counterion. The fluorescence property for all of the viologen polymers in either aqueous or methanol solution was also included in this study. For example, the viologen polymer containing the 4,4′‐bipyridinium and p‐xylyl units along the backbone of the polymer chain with triflimide as a counterion had an absorption spectrum (λ_max = 265 nm), an excitation spectrum (λ_ex values = 357, 443, and 454 with monitoring at 533 nm), and an emission spectrum (λ_em = 536 nm with excitation at 430 and 450 nm) in methanol. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 659–674, 2002; DOI 10.1002/pola.10134     

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

In this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C₆(mim)]⁺_X^?, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C₆(mim)₂X₂], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl^? and Br^? anions prefer to locate almost in the plane of the imidazolium ring whereas the I^? anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl^? and Br^? anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.     

Photochromic and photomechanical ionene elastomer containing poly(tetrahydrofuran) segments and viologen units

Elastomeric polymer consisting of poly(oxytetramethylene) segments and viologen units (PTV) was synthesized by the reaction of dicationic living poly(tetrahydrofuran) with 4,4′-bipyridine at ?70°C. The chloride or bromide ion was introduced as the counter anion into the viologen groups of PTV by the treatment of the reaction mixture with aqueous sodium chloride or bromide, respectively. The solid film of PTV having chloride inon showed photochromism, i.e., color change by light irradiation, via photoreduction of the violegen groups. In contrast. PTV of bromide counter anion required a small amount of poly(N-vinyl-2-pyrrolidone) to undergo the photochromic reaction. The irradiation of light also affected the stress relaxation of the polymers, namely PTV showed photomechanical behavior. This phenomenon is considered to be induced by the decrease of total number of ionic charges of PTV by photo-reduction of the viologen groups followed by the change of a state of ionic clustering in the polymer matrix.     

On the importance of the nature of the ionic liquids in the selective simultaneous separation of the substrates and products of a transesterification reaction through supported ionic liquid membranes

Previously, we reported the selective simultaneous separation of the substrates and products of a transesterification reaction (vinyl butyrate, 1-butanol, butyl butyrate, and butyric acid) through supported liquid membranes (SLMs) based on two ionic liquids (ILs): 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim⁺][PF₆⁻], and 1-octyl-3-methylimidazolium hexafluorophosphate, [omim⁺][PF₆⁻]. The significant differences observed in the selectivity values, attributed to the different nature of the ionic liquid phase used, led us to further investigate this matter.