Alkylimidazolium Cations Research Articles

Unusually Large Ligand Field Splitting in Anionic Europium(III) Complexes Induced by a Small Imidazolic Counterion.

Luminescent trivalent lanthanide (Ln3+) complexes are compounds of technological interest due to their unique photophysical properties, particularly anionic tetrakis complexes, given their higher stability and emission quantum yields. However, structural studies on the cation-anion interaction in these complexes and the relation of such to luminescence are still lacking. Herein, the cation-anion interactions in two luminescent anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III) complexes with alkylimidazolium cations, specifically 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium are investigated. The Eu3+ complexes were synthesized and characterized by elemental analysis, mass spectrometry, and single-crystal X-ray crystallography, and their luminescence spectra were recorded at 77 K. Quantum chemical calculations were also performed. X-ray crystallography revealed hydrogen bonds between the enolate ligands and imidazolium ring hydrogens. The 1-butyl-3-methylimidazolium complex had two crystallographic Eu3+ sites, also confirmed by luminescence spectroscopy. The 1-ethyl-3-methylimidazolium complex exhibited an unusual 300 cm-1 splitting in the 5D0 → 7F1 transition, as reproduced by ligand field calculations, suggesting a stronger hydrogen bonding due to the smaller substituent. We hypothesize that this strong bonding likely causes angular distortions, resulting in high ligand field splittings.

Short alkyl-imidazolium ionic liquids enhanced in-situ transesterification of microalgae

Ionic liquids (ILs) catalyzed in-situ transesterification (IST) of microalgae is a promising strategy to improve biodiesel yield through enhancing cellulose solubility and catalyzing transesterification. Effect of anions of ILs on biodiesel has been widely investigated previously. However, how do cations of ILs affect IST of microalgae is still unclear. On this basis, ILs composed of alkyl-imidazolium cations with different length, 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), and 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF4]) catalyzed IST of microalgae are experimentally and theoretically investigated. The results indicate that increasing alkyl chains of cations weakens interactions of ILs-cellulose, and reduces acidities of ILs, subsequently leads to decrease of cellulose extraction yield and biodiesel yield. Although cellulose extraction yield and biodiesel yield are affected by reaction temperature, dosage of methanol, and MILs: Algae, however, H-bonding interactions of ILs-cellulose and acidities of ILs are still dominate parameters affecting cellulose extraction yield and biodiesel yield, respectively, leading to their unchanged sort under variable reaction conditions as following: [Emim][BF4] > [Bmim][BF4] > [Hmim][BF4]. This work reveals that short alkyl chain of cation is favorable to both cellulose extraction and biodiesel yield, providing theoretical guides for screen and design of benign ILs to further improve biodiesel of in-situ transesterification of microalgae.

Influence of the Deposition Rate and Substrate Temperature on the Morphology of Thermally Evaporated Ionic Liquids

The wetting behavior of ionic liquids (ILs) on the mesoscopic scale considerably impacts a wide range of scientific fields and technologies. Particularly under vacuum conditions, these materials exhibit unique characteristics. This work explores the effect of the deposition rate and substrate temperature on the nucleation, droplet formation, and droplet spreading of ILs films obtained by thermal evaporation. Four ILs were studied, encompassing an alkylimidazolium cation (CnC1im) and either bis(trifluoromethylsulfonyl)imide (NTf2) or the triflate (OTf) as the anion. Each IL sample was simultaneously deposited on surfaces of indium tin oxide (ITO) and silver (Ag). The mass flow rate was reproducibly controlled using a Knudsen cell as an evaporation source, and the film morphology (micro- and nanodroplets) was evaluated by scanning electron microscopy (SEM). The wettability of the substrates by the ILs was notably affected by changes in mass flow rate and substrate temperature. Specifically, the results indicated that an increase in the deposition rate and/or substrate temperature intensified the droplet coalescence of [C2C1im][NTf2] and [C2C1im][OTf] on ITO surfaces. Conversely, a smaller impact was observed on the Ag surface due to the strong adhesion between the ILs and the metallic film. Furthermore, modifying the deposition parameters resulted in a noticeable differentiation in the droplet morphology obtained for [C8C1im][NTf2] and [C8C1im][OTf]. Nevertheless, droplets from long-chain ILs deposited on ITO surfaces showed intensified coalescence, regardless of the deposition rate or substrate temperature.

Nucleation, Coalescence, and Thin-Film Growth of Triflate-Based Ionic Liquids on ITO, Ag, and Au Surfaces

This study investigates the nucleation and growth of micro-/nanodroplets of triflate-based ionic liquids (ILs) fabricated by vapor deposition on different surfaces: indium tin oxide (ITO); silver (Ag); gold (Au). The ILs studied are constituted by the alkylimidazolium cation and the triflate anion—[CnC1im][OTF] series. One of the key issues that determine the potential applications of ILs is the wettability of surfaces. Herein, the wetting behavior was evaluated by changing the cation alkyl chain length (C2 to C10). A reproducible control of the deposition rate was conducted employing Knudsen cells, and the thin-film morphology was evaluated by high-resolution scanning electron microscopy (SEM). The study reported here for the [CnC1im][OTF] series agrees with recent data for the [CnC1im][NTf2] congeners, highlighting the higher wettability of the solid substrates to long-chain alkylimidazolium cations. Compared to [NTf2], the [OTF] series evidenced an even more pronounced wetting ability on Au and coalescence processes of droplets highly intense on ITO. Higher homogeneity and film cohesion were found for cationic groups associated with larger alkyl side chains. An island growth was observed on both Ag and ITO substrates independently of the cation alkyl chain length. The Ag surface promoted the formation of smaller-size droplets. A quantitative analysis of the number of microdroplets formed on Ag and ITO revealed a trend shift around [C6C1im][OTF], emphasizing the effect of the nanostructuration intensification due to the formation of nonpolar continuous domains.

Quantum chemical calculations of formation enthalpies of cations and anions of ionic liquids

The development of advanced ionic-liquid-based applications requires accurate thermochemical data for both ionic liquids and their constituent ions. Herein, the formation enthalpies of alkylimidazolium cations ([CnMIm+], n = 2, 4, 6, 8, 10) and various anions (trifluoromethanesulfonate ([TfO−]), ethyl sulfate ([ES−]), dicyanamide ([DCA−]), and bis(trifluoromethane)sulfonylimide ([NTf2−])) in the ideal gas state were obtained by quantum chemical calculations using density functional theory (DFT: B3LYP, B98, M06, M06-2X) and composite (G4) thermochemical models in the framework of the isodesmic reaction approach. The enthalpies of heterolytic dissociation of neutral ion pairs (NIPs) for the [CnMIm+][X−] series (n = 2, 4, 6, 8, 10; X− = [TfO−], [ES−], [NTf2−], [DCA−], [BF4−], [PF6−], [Cl−], [Br−], [I−]) were derived using the obtained data and literature formation enthalpies (ΔfH°) of NIPs. Analysis of the thermochemical property trends revealed that the formation enthalpies of [CnMIm+] decrease linearly as the alkyl chain length increases. In addition, the use of the isodesmic reaction approach improved the reliability of the computed data. Furthermore, owing to its internal self-consistency, the G4 method was found to be the most appropriate for describing the thermodynamic quantities of the cations and anions of ionic liquids.

Alkylimidazolium Protic Ionic Liquids: Structural Features and Physicochemical Properties.

We focus on a series of protic ionic liquids (PILs) with imidazolium and alkylimidazolium (1R3HIm, R=methyl, ethyl, propyl, and butyl) cations. Using the literature data and our experimental results on the thermal and transport properties, we analyze the effects of the anion nature and the alkyl radical length in the cation structure on the above properties. DFT calculations in gas and solvent phase provide further microscopic insights into the structure and cation-anion binding in these PILs. We show that the higher thermodynamic stability of an ion pair raises the PIL decomposition temperature. The melting points of the salts with the same cation decrease as the hydrocarbon radical in the cation becomes longer, which correlates with the weaker ion-ion interaction inthe ion pairs. A comparative analysis of the protic ILs and corresponding ILs (1R3MeIm) with the same radical (R) in the cation structure and the same anion has been performed. The lower melting points of the ILs with 1R3MeIm cations are assumed to result from the weakening of both the ion-ion interaction and the hydrogen bond.

Carboxylate functionalized imidazolium-based zwitterions as benign and sustainable solvent for cellulose dissolution: Synthesis and characterization

Cellulose is most abundant biopolymer on earth and can be utilized as sustainable resources for many applications, however, their utilization at great extent is limited due to lack of benign and recyclable solvent. While N-methylmorpholine-N-oxide (NMMO), used in Lyocell process, is thermally unstable and may undergoes runaway conditions, commercialization of ionic liquid as solvent still suffers from recyclability issues. Herein, we present the synthesis of a series of zwitterions, composed of tethered alkyl imidazolium cation and carboxylate anion, and investigated their cellulose dissolution characteristics. Effect of alkyl chain length of imidazolium ring on its dissolution efficiencies was studied and amongst synthesized zwitterions, the hexanoate derivatives exhibited 13% (w/w) cellulose dissolution at 100–125 °C. Thermal stability of zwitterions and their cellulose solution was characterized by DSC-TGA and found to be more stable than the NMMO and Lyocell solution. Rheological studies indicate that cellulose solution in zwitterions are viscoelastic and in spinnable range of fibre processing. Structural and morphological characterization of regenerated cellulose using elemental analysis, FTIR, DSC-TGA, GPC, XRD and SEM showed that zwitterions have no adverse effect on its physicochemical and morphological properties. A method for recovery and purification of solvent after cellulose dissolution and regeneration is also presented.

New catalytic systems with chemically fixed nickel complexes in the reactions of reductive activation of C-F bonds in ionic liquid media

The nickel complexes with bidentate nitrogen-containing ligands covalently bound to alkylimidazolium cations were obtained for the first time. By the example of the reaction of selective hydrodefluorination of hexafluorobenzene to pentafluorobenzene, it was shown that the catalytic systems ionic liquid - water - covalently bound nickel complex based on the obtained compounds are much more efficient with repeated use in comparison with unfixed nickel complexes. The decisive influence of the cationic fragment of the ionic liquid on the possibility of multiple use of nickel complexes has been established.

Paving the way to solubility through volatility: Thermodynamics of imidazolium-based ionic liquids of the type [CnC1Im][I

Ionic liquids are effectively used for manufacturing of nanoparticles for thermoelectric generators and in the field of hydrogen storage. Development and optimization of these processes require knowledge of the thermodynamic properties of ionic liquids. Thermochemical study of the series of 1-alkyl-3-methylimidazolium iodides is presented in this work. Vapor pressures and vaporization enthalpies have been measured by using quartz-crystal microbalance. Solution enthalpies were measured by using solution calorimetry. Thermodynamics of aqueous solutions, solubility parameters and miscibility of ILs in eleven organic solvents were derived and discussed. The absence of thermal decomposition of [C4C1Im][I] under vaporization conditions has been demonstrated experimentally and theoretically. It has been shown that vaporization enthalpies are linearly dependent on the chain length of the alkyl substituent and linearly dependent on the surface tension. Aqueous-phase enthalpies of formation of alkyl imidazolium cations have been derived with help of solution calorimetry.

Protic Ionic Liquids Based on the Alkyl-Imidazolium Cation: Effect of the Alkyl Chain Length on Structure and Dynamics.

Protic ionic liquids are known to form extended hydrogen-bonded networks that can lead to properties different from those encountered in the aprotic analogous liquids, in particular with respect to the structure and transport behavior. In this context, the present paper focuses on a wide series of 1-alkyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [HC nIm][TFSI], with the alkyl chain length ( n) on the imidazolium cation varying from ethyl ( n = 2) to dodecyl ( n = 12). A combination of several methods, such as vibrational spectroscopy, wide-angle X-ray scattering (WAXS), broadband dielectric spectroscopy, and 1H NMR spectroscopy, is used to understand the correlation between local cation-anion coordination, nature of nanosegregation, and transport properties. The results indicate the propensity of the -NH site on the cation to form stronger H-bonds with the anion as the alkyl chain length increases. In addition, the position and width of the scattering peak q1 (or the pre-peak), resolved by WAXS and due to the nanosegregation of the polar from the nonpolar domains, are clearly dependent on the alkyl chain length. However, we find no evidence from pulsed-field gradient NMR of a proton motion decoupled from molecular diffusion, hypothesized to be facilitated by the longer N-H bonds localized in the segregated ionic domains. Finally, for all protic ionic liquids investigated, the ionic conductivity displays a Vogel-Fulcher-Tammann dependence on inverse temperature, with an activation energy Ea that also depends on the alkyl chain length, although not strictly linearly.

Molecular Mechanisms Underlying Inhibitory Binding of Alkylimidazolium Ionic Liquids to Laccase.

Water-miscible alkylimidazolium ionic liquids (ILs) are “green” co-solvents for laccase catalysis, but generally inhibit enzyme activity. Here, we present novel insights into inhibition mechanisms by a combination of enzyme kinetics analysis and molecular simulation. Alkylimidazolium cations competitively bound to the TI Cu active pocket in the laccase through hydrophobic interactions. Cations with shorter alkyl chains (C2~C6) entered the channel inside the pocket, exhibiting a high compatibility with laccase (competitive inhibition constant Kic = 3.36~3.83 mM). Under the same conditions, [Omim]Cl (Kic = 2.15 mM) and [Dmim]Cl (Kic = 0.18 mM) with longer alkyl chains bound with Leu296 or Leu297 near the pocket edge and Leu429 around TI Cu, which resulted in stronger inhibition. Complexation with alkylimidazolium cations shifted the pH optima of laccase to the right by 0.5 unit, and might, thereby, lead to invalidation of the Hofmeister series of anions. EtSO4− showed higher biocompatibility than did Ac− or Cl−, probably due to its binding near the TI Cu and its hindering the entry of alkylimidazolium cations. In addition, all tested ILs accelerated the scavenging of 2, 2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radicals, which, however, did not play a determining role in the inhibition of laccase.

Ionothermal Design of Crystalline Halogeno(cyano)cuprate Family: Structure Diversity, Solid-State Luminescence, and Photocatalytic Performance.

A general preparative method for multifunctional halogeno(cyano)cuprate materials in ionic liquids is developed in this work. Under ionothermal conditions, alkylimidazolium-based ionic liquids serving as solvent, charge-compensating, and structure-directing agent, as well as reactant lead to 12 members of the novel hybrid halogeno(cyano)cuprate family with a general formula of [R1R2R3IM]b+c-a[CuaXb(CN)c] (R1R2R3IM = alkylimidazolium cations, X = halide anions). X-ray single-crystal diffractions show that diverse inorganic halogeno(cyano)cuprate components vary from discrete complexes (1 and 2), one-dimensional (1D) chains (3-7), two-dimensional (2D) layer (8), to three-dimensional (3D) open frameworks (9-12). 1 and 2 are of zero-dimensional discrete structures containing triangular [CuX3]2- anions. In complexes 3-7, pentagonal bipyramidal [Cu2X3] units are bridged by CN groups to give 1D [Cu2X3(CN)]2- inorganic chains, which are charge-balanced by the surrounded alkylimidazolium cations. 2D inorganic [Cu5ClI2(CN)4]2- layer in complex 8 is alternately packed with [VMIM]+ organic cations. In complex 9, left- and right-handed Cu-CN helical chains connect each other to give a 3D open framework, which are further entrapped by 1D zigzag Cu-CN chains and [PMIM]+ cations. Diverse unique Cu(I) atoms and cyanide or halide bridging groups in 10, 11, and 12 are extended into 3D anionic open frameworks with 1D channels, which are occupied by alkylimidazolium cations. For all hybrid halogeno(cyano)cuprate complexes, the extensively existing C-H···X or C-H···π hydrogen bonds help to stabilize the ultimate supramolecular packing structures. Notably, the distances between adjacent Cu(I) centers range from 2.420(2) to 2.989(2) Å in all polymeric frameworks, which indicate strong Cu···Cu interactions. Thanks to the cooperation of conjugate π electron cyanide systems with halide ions and/or Cu···Cu interactions, compounds 1-12 all demonstrate strong solid-state photoluminescence and semiconducting performance. Specially, hybrid halogeno(cyano)cuprates reported herein first exhibit excellent photocatalytic degradation of organic dye. To the best of our knowledge, fewer than 10 crystalline halogeno(cyano)cuprate compounds were obtained before this work, although different synthetic routes have been involved. Clearly, the discovery of this large hybrid material family under ionothermal conditions is important for the further development of novel functional halogeno(cyano) filled-shell d10 metal crystalline materials.

Effect of microwave irradiations on the sorption of alkylimidazolium salts on bentonite

Sorption study of alkylimidazolium salts on a bentonite aims at elaborating organophilic organoclay materials likely to be used in the separation of organic compounds of diverse polluted effluents. Therefore, the action of bromide and hexafluorophosphate salts of several alkyl-3-methylimidazolium, with long hydrocarbon chains (C10–C18), on a calcic bentonite was followed by several analysis methods. The analysis results reveal the insertion of alkylimidazolium cations between layers of clay, the adsorption extent of alkylimidazolium salts on surfaces of treated clays and presence of bonds relative to fixed organic salts. The contribution of activation by microwave irradiations on adsorption and insertion of bentonite was also studied (90 W for 5–30 min) and the obtained results were compared with those obtained under classical conditions (room temperature for 24 h). It was found that adsorption and intercalation capacities become quicker and more important under microwave activation. This insertion phenomenon becomes more and more significant with the irradiation time and the excess of imidazolium salts. The original point of the paper carries on the activation by microwave irradiations on bentonite insertion.

Elucidation of the Morphology of Imidazolium-Based Anion Exchange Membranes for Alkaline Anion Fuel Cells

Due to the growing concerns on the depletion of petroleum based energy resources and the climate change, polymer electrolyte membrane fuel cells (FCs) technologies have received much attention in recent years owing to their high efficiencies and low emissions. Among them, alkaline anion exchange membrane fuel cell (AEM-FC) is a good choice, because it avoids the consumption of acid-resistant precious metal catalysts and costs up. However, the biggest challenge in developing AEM-FCs is to fabricate AEM with high ion conductivity and mechanical stability without chemical deterioration at elevated pH and temperatures. So far, most strategies were focused on synthesizing new thermally and chemically durable fluorinated and aromatic polymers. For the first time, our group tried to develop the new type of 2Me-AEMs by radiation-induced grafting of 2-methyl-1-vinylimidazole and styrene into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and a subsequent N-alkylation with methyliodide. The resultant AEMs exhibit high ion conductivity (> 100 mS/cm) and longer alkaline durability, owing to the fact that the methyl protecting group at 2-imidazole position prevented the ring-opening degradation. 2Me-AEM with an IEC(ion exchange capacity) of 1.82 mmol/g shows the best well-balanced properties required for fuel cell applications. All these findings on one hand, are the result of sample preparation procedure of the radiation grafting method and the introduction of alkylimidazolium cations as an anion conducting group, and on the other hand, are believed to be controlled by the microphase separated structures of the membranes in the hydrated state. In this work, we aim to elucidate the morphology of these 2Me-AEMs and understand the structure related unique properties such as the mechanical property and the anion conductivity. We investigated the morphology and swelling behavior of these new graft-type AEMs by using contrast variation small angle neutron scattering (SANS) technique, performed mainly on KWS-2 SANS diffractometer operated by Juelich Centre for Neutron Science at the neutron source Heinz Maier-Leibnitz (FRM II reactor) in Garching, Germany. Our results showed that the scattering intensity and the shape of the profiles vary significantly upon grafting, but change little upon alkylation; while the incorporation of water in the hydrophilic domains upon swelling, not only increases the intensity and domain size, but also leads to the excess scattering at high-q region with q being the scattering vector. From these results, we concluded that the crystalline lamellar and crystallite structures originating from the pristine ETFE films were more or less conserved in these AEMs, but the lamellar d-spacing in both dry and wet membranes were enlarged, indicating an expansion of the amorphous lamellae due to the graft chains introduced in the grafting process and the water incorporated in the swelling process. We further quantitatively studied the swelling behavior of the AEMs in various water mixtures of water and deuterated water with different volume ratios (contrast variation method), and the morphology of these membranes was elucidated by three phases: phase 1) crystalline ETFE domains, which offer good mechanical properties; phase 2) hydrophobic amorphous domains, which are made up of amorphous ETFE chains and offer a matrix to create conducting regions; phase 3) interconnected hydrated domains, which are composed of the entire graft chains and water and play a key role to promote the conductivity.

Tunable Aryl Alkyl Ionic Liquids with Weakly Coordinating Tetrakis((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)borate [B(hfip)4 ] Anions.

Weakly coordinating borate or aluminate anions have recently been shown to yield interesting properties of the resulting ionic liquids (ILs). The same is true for large phenyl-substituted imidazolium cations, which can be tuned by the choice, position, or number of substituents on the aromatic ring. We were therefore interested to combine these aryl alkyl imidazolium cations with the weakly coordinating tetrakis((1,1,1,3,3,3-hexafluoropropan-2-yl)oxy)borate [B(hfip)4 ](-) anions to study the physical properties and viscosities of these ionic liquids. Despite the large size and high molecular weight of these readily available ILs, they are liquid at room temperature and show remarkably low glass transition points and relatively high decomposition temperatures.

Electrochemical and physicochemical properties of redox ionic liquids using electroactive anions: influence of alkylimidazolium chain length

Ferrocenylsulfonyl(trifluoromethylsulfonyl)imide [FcNTf] is reported as a redox anionic species used to obtain an electroactive ionic liquid with a typical alkylimidazolium cation. Here, several of these redox ionic liquids (RILs) were prepared by combining FcNTf with alkylimidazolium cations in order to understand the influence of symmetry and alkyl chain length on the RIL system. The physicochemical and electrochemical properties are characterized for [CxCyIm][FcNTf], where x and y were varied between 1 and 8, both in the pure, undiluted state and in solutions of acetonitrile. In pure form, the ionic conductivity of [CxCyIm][FcNTf] was found to range between 0.22 and 0.42mScm−1 at 60°C, and the alkyl chain length was found to have a similar effect on viscosity as in conventional imidazolium-NTf2 ionic liquids. While an increase in alkyl chain length increases viscosity and decreases mass transport, it was found to have no effect on the redox potential of the ferrocene center. The cyclic voltammetry of [CxCyIm][FcNTf] solutions diluted in acetonitrile exhibited behavior which depends on concentration and on the presence of a supporting electrolyte. At concentrations above 50wt.% and in the absence of any supporting electrolyte, the electroactive anion was found to deposit as a dense film on the electrode upon oxidation. This behavior is linked to formation of Fc+NTf− zwitterions, which accumulates in the double-layer and precipitates on the electrode surface. This study also investigates the electrochemical properties of film deposition.

Polymerization of vinyl fluoride in ionic liquid and ionic solutions

Poly(vinyl fluoride) films are extensively used as protective, easy-clean materials in the photovoltaic and aerospace industries. However, polymerization of vinyl fluoride (VF) monomer typically requires high pressures (>5000 psi) due to the low solubility of VF monomer in the aqueous polymerization medium. VF was found to exhibit high solubilities in fluorinated ionic liquids and concentrated aqueous ionic salt solutions at low pressures (<1000 psi). Polymerization of vinyl fluoride in the presence of ionic liquids or ionic salt solutions was pursued as a means of reducing the pressure needed to achieve high monomer conversion and molecular weight. The use of traditional ionic liquids possessing alkylimidazolium cations paired with fluorinated anions as solvents for VF polymerization resulted in poor conversion of vinyl fluoride, likely due to hydrogen atom abstraction from the alkyl substituents on the imidazolium cations. Polymerization of VF in the presence of lithium salts of the ionic liquid anions (trifluoromethylsulfonyl imide [Tf2N], triflate, and trifluoroacetate), on the other hand, resulted in high VF conversion and production of high molecular weight polymer at low VF pressures. The morphology of the resultant polymer consisted of fractal-like aggregates, and mixtures of the polymer with the aqueous ionic salt solutions formed viscous pastes.

Solvatochromic polarity parameters for binary mixtures of 1-butyl-3-methylimidazolium acetate with water, methanol, and dimethylsulfoxide

Solvatochromic polarity parameters (ETN, a, β, and π*) for binary mixtures of 1-butyl-3-methylimidazolium acetate-ionic liquid, which is a promising solvent of lignocellulosic materials with water, methanol, and dimethylsulfoxide, are determined via UV spectroscopy. A Redlich-Kister (CNIBS/R-K) equation modified for a quasi-ideal binary solvent is used to describe algebraically the dependences between the Dimroth-Reichardt energies, the Kamlet-Taft parameters, and the composition of binary mixtures. The addition of molecular solvents to the ionic liquid in significant amounts was shown to produce no radical changes in its polarity or donor and acceptor characteristics, due to the incorporation of a cosolvent into supramolecular clusters formed by alkylimidazolium cations.

Cholesteryl-containing ionic liquid crystals composed of alkylimidazolium cations and different anions

Cholesteryl-containing ionic liquid crystals (ILCs) 1-cholesteryloxycarbonylmethyl(propyl)-3-methyl(butyl)imidazolium chlorides ([Ca-Me-Im]Cl, [Ca-Bu-Im]Cl, [Cb-Me-Im]Cl and [Cb-Bu-Im]Cl) and corresponding imidazolium tetrachloroaluminates ([Ca-Me-Im]AlCl4, [Ca-Bu-Im]AlCl4, [Cb-Me-Im]AlCl4 and [Cb-Bu-Im]AlCl4) were synthesized in this work, and the chemical structure, LC behavior and ionic conductivity of all these ILCs were characterized by several technical methods. The imidazolium-based salts with Cl− ions showed chiral smectic A (SA*) phase on both heating and cooling cycles, while the tetrachloroaluminates exhibited chiral nematic (N*) phase. The mesophase was confirmed by characteristic LC textures observed by polarizing optical microscopy and typical diffractogram obtained by X-ray diffraction measurements. The samples with similar cholesteryl-linkage component showed similar phase transition temperature and entropy, indicating the cholesteryl component influence predominately on the phase transition rather than alkyl substituents on the imidazole ring. The imidazolium tetrachloroaluminates display relatively low phase transition temperature compared with the precursor chlorides. The functional difference in LC behavior and ionic conductivity were discussed by investigated the structural difference between the Cl−-containing and AlCl4—containing materials. The imidazolium chlorides exhibited layer structure both in crystal and mesophase states, and should be organized with a ‘head-to-tail’ organization to form interdigitated monolayer structures due to the tight ion pairs. But the imidazolium tetrachloroaluminates displayed layer structure only in crystal phase, and should be organized in ‘head-to-head’ arrangements form bilayer structures due to loose combination of ion pairs despite of hydrogen-bond and electrostatic attraction interaction.

Imidazolium Cation Based Anion-Conducting Electrolyte Membranes Prepared by Radiation Induced Grafting for Direct Hydrazine Hydrate Fuel Cells

Graft-type anion-conducting electrolyte membranes (AEMs) with imidazolium cations on graft polymers were synthesized through radiation-induced graft polymerization of N-vinylimidazole (NVIm) on poly(ethylene-co-tetrafluoroethylene) (ETFE) films, followed by N-propylation and ion-exchange reactions. The N-propylation proceeded quantitatively, whereas the ion-exchange reactions in 1 M KOH at 60°C were accompanied by partial β-elimination of the imidazolium cations to yield copolymer grafts consisting of poly-(1-vinyl-3-propylimidazolium hydroxide) and double bonds (polyethyne) (AEM2), which exhibited an ion-exchange capacity (IEC) of 0.85 mmol g−1 and ionic conductivity of 10 mS cm−1. AEM2 showed alkaline stability at 60°C but it gradually degraded at 80°C for ca. 150 h. The copolymer-type AEM (AEM3) with an IEC of 1.20 mmol g−1 was prepared through the copolymerization of NVIm with styrene on ETFE films, followed by the same N-propylation and ion-exchange reactions. AEM3 was characterized to be a terpolymer, owing to partial β-elimination and showed higher alkaline durability in 1 M KOH at 80°C. As a result, it exhibited higher conductivity (>10 mS cm−1) for 250 h. Therefore, alkylimidazolium cations in copolymer grafts are a promising anion conducting group for alkaline-durable AEMs. A maximum power density of 75 mW cm−2 is obtained for AEM3 in a direct hydrazine hydrate fuel cell.