Aggregates in mixtures of ionic liquids

Surfactant-like ionic liquids (C₁₆MIMCl, C₁₆MIMBF₄) aggregate in mixtures with another ionic liquid (EAN). Critical aggregate concentrations and estimations of object sizes are given and compared to aqueous systems and other relevant literature data. The investigated mixtures are stable up to more than 200 °C and can probably be used to extend the limited temperature range of water-based colloids.     

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH₃CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH₃CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH₃CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν₁ (CD₃ ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd.     

The physical properties of aqueous solution of room-temperature ionic liquids based on imidazolium: Database and evaluation

We report the systematic studies of the physical properties of systems involving imidazolium based ionic liquids and water. The measurements of density ρ, refractive index Δ_n, viscosity η, specific conductance κ and surface tension γ were made over the whole concentration range. The equivalent conductivity Λ_m was calculated. The physical properti`es of the solutions changed with the change of association between ionic liquid and water. The physical properties of the solutions also vary with the alkyl length on the cation and polarity of anion.     

Prediction carbon dioxide solubility in ionic liquids based on deep learning

Ionic liquids have a great potential in capture and separation of carbon dioxide (CO₂), and the solubility of CO₂ in ionic liquids is one of key data for engineering applications. In this paper, the critical properties of ionic liquids are combined with deep learning models (CP-DNN, CP-CNN, CP-RNN) to establish theoretical prediction models of CO₂ solubility in ionic liquids. The predictive performance of these framworks is able to meet or exceed the predicted effects of the method based on thermodynamic models (PR,SRK) and machine learning method (XGBoost). For CP-RNN, the coefficient of determination (R²) between experimental and predicted values is 0.988, CP-CNN is 0.999, and CP-DNN is 0.984. This research can avoid complex computational characterisation, it is to provide a theoretical method to further enrich and improve the data information analysis of the solubility of CO₂ in ionic liquids.     

Physicochemical properties of ionic liquids based on imidazolium/pyrrolidinium cations and maleate/phthalate anions

Ionic liquids (ILs) based on imidazolium/pyrrolidinium cations and maleate/phthalate anions can be used as excellent electrolyte materials for electrolytic capacitors. In this study, we synthesized four ILs of this family and investigated their thermal behaviors, ionic conductivities and sparking voltages. The four ILs have high thermal stability for capacitor requirements. The conductivities of imidazolium ILs are slightly higher than those of pyrrolidinium analogs and the conductivities of maleate anion-based ILs are higher than those of corresponding phthalate anion-based ILs. Besides, the long-term thermal stability of imidazolium ILs in conductivity is superior to that of pyrrolidinium analogs. Whereas the long-term thermal stability of phthalate anion-based ILs is better than that of corresponding maleate anion-based ILs. The influence of cationic structure of the ILs on conductivity was analyzed. The temperature dependence of conductivity was also discussed in this work. The Vogel–Tammann–Fulcher (VTF) equation accurately describes the temperature dependence of conductivity for the ILs. In addition, the result of sparking voltage measurement shows that neither Ikonopisov nor Albella model is valid for the ILs.     

Potentialities of ionic liquids as new electrolyte media in advanced electrochemical devices

This paper reviews the various classes of ionic liquids (ILs) in view of their established and expected applications in advanced electrochemical devices, such as lithium batteries, fuel cells, and supercapacitors. In this respect, particular attention is devoted to aprotic and protic ILs, with a related discussion in terms of their thermal and transport properties. In addition, the role in the electrochemical technology of a new class of ILs having cation and anion tethered in an intramolecular form is stressed. Due to their emerging importance, IL-based polymers are finally reported and discussed. A conclusion, where the expected evolution of the ILs research and development is evaluated, is also included.     

The effect of ionic liquids on the conductivity of electrospun polyacrylonitrile membranes

Adding conductive additives to electrospinning solutions has been proven to increase the conductivity of electrospun membranes. The aim of this study was to learn the effect of ionic liquids (ILs) on the polyacrylonitrile membranes conductivity. Three different ionic liquids were used with concentration to 10 wt%. The conductivity of the membranes increases from picoS range without using IL to microS range with adding IL. At concentration 8 wt% ILs the percolation threshold was observed with maximum conductivity of the electrospun membranes. The maximum conductivity was measured to be 2.39 μS/cm.     

Tribological properties of Ti-doped DLC coatings under ionic liquids lubricated conditions

In this paper, titanium doped diamond-like carbon (Ti-DLC) coatings were prepared onto AISI 52100 steel substrates using medium frequency magnetic sputtering process, and were analyzed using the Raman and transmission electron microscope (TEM). Two kinds of 1,3-dialkyl imidazolium ionic liquids (ILs) were synthesized and evaluated as lubricants for Ti-DLC/steel contacts at room temperature, and PFPE as comparison lubricant. The tribological properties of the ILs were investigated using a ball-on-disk type UMT reciprocating friction tester. The results indicated that the ILs have excellent friction-reducing properties, the friction coefficient kept at a relatively stable value of 0.07-0.06, which was reduced approximately by 47% compared with perfluoropolyether (PFPE). The worn surfaces of Ti-DLC coatings were observed and analyzed using a MICROXAM-3D non-contact surface profiler, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The Ti-DLC coatings using ionic liquids lubricating systems are considered as potential lubricating system in vacuum and space moving friction pairs.     

An efficient enzymatic modification of cordycepin in ionic liquids under ultrasonic irradiation

A comparative study of the immobilized Candida antarctica lipase B (Novozym 435)-catalyzed acylation of cordycepin with vinyl acetate in ionic liquids (ILs) under ultrasonic irradiation and shaking was conducted. The application of ultrasonic irradiation instead of shaking during acylation resulted in an enhanced reaction rate and a higher level of substrate conversion. Among the various ILs examined, 1-butyl-3-methylimidazolium tetrafluorobrate ([C₄MIm][BF₄]) was the best medium for the reaction because it produced the highest substrate conversion. In [C₄MIm][BF₄], the optimal ultrasonic power, water activity, and reaction temperature were 120 W, 0.33, and 50 °C, respectively. The acylation of cordycepin in [C₄MIm][BF₄] proved to be regioselective under both conditions: the C5′-OH was acylated. Novozym 435 exhibited a much higher operational stability in [C₄MIm][BF₄], and 58.0% of its original activity was maintained after ten reuse cycles under ultrasonic irradiation. Compared with the cordycepin, the rate of adenosine deaminase-catalyzed deamination was greatly reduced when the 5′-OH was substituted by acetyl group. These results demonstrated that the combined application of ultrasonic irradiation and IL as a medium was an efficient approach for the enzymatic modification of cordycepin.     

Temperature effect on the molecular interactions between two ammonium ionic liquids and dimethylsulfoxide

To understand the molecular interactions between newly synthesized ammonium ionic liquids (ILs) and highly polar solvent dimethylsulfoxide (DMSO), precise measurements such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been performed over the whole composition range at temperature ranging from 298.15 to 308.15 K and at atmospheric pressure. The ILs investigated in the present study included diethyl ammonium acetate ([Et₂NH][CH₃COO], DEAA) and triethyl ammonium acetate ([Et₃NH][CH₃COO], TEAA). Further, to gain some insight into the nature of molecular interactions in these mixed solvents, we predicted the excess molar volume (V^E), the deviation in isentropic compressibilities (ΔK_s) and deviation in viscosity (Δη) as a function of the concentration of IL using the measured properties of ρ, u and η, respectively. Redlich-Kister polynomial was used to correlate the results. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and DMSO molecules and their structural factors.     

A FT-IR spectroscopic study of ultrasound effect on aqueous imidazole based ionic liquids having different counter ions

Ultrasound (US) effect on 1-butyl-3-methyl-imidazolium (BMI) ionic liquids having different counter anions, BF₄⁻, PF₆⁻ and Cl⁻ in aqueous medium was studied by FT-IR spectroscopy. Their deconvolution spectra were used to analyze the change of hydrogen bond in the absence and presence of US exposure to the ionic liquid. The FT-IR spectra were measured in different water contents without and with US at 23 kHz. These results indicated that the counter anion species in the imidazole based the ionic liquids played an important role for water solvation, when the US was exposed. The US hardly changed hydrogen bonding in the aqueous BMI–PF₆, while the BMI–BF₄ and BMI–Cl showed obvious change in their FT-IR spectra. Especially for the BMI–Cl, significant change was observed by the US exposure in the range of 2.6 wt% to 20 wt% of water contents. The results showed that the US could break the hydrogen bond in the BMI–Cl ionic liquids. In the case of BMI–BF₄, the FT-IR band at 950–1152 cm⁻¹ was significantly intensified under US exposure, due to that the US influenced BF₄⁻-water interaction. But, it was observed that the ionic liquid having PF₆⁻ was very less changed in the US system.     

Study of surface interactions of ionic liquids with aluminium alloys in corrosion and erosion-corrosion processes

Surface interactions of alkylimidazolium ionic liquids (ILs) with aluminium alloy Al 2011 have been studied by immersion tests in seven neat ILs [1-n-alkyl-3-methylimidazolium X⁻ (X = BF₄; n = 2 (IL1), 6 (IL2), 8 (IL3). X = CF₃SO₃; n = 2 (IL4). X = (4-CH₃C₆H₄SO₃); n = 2 (IL5). X = PF₆; n = 6 (IL6)] and 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide (IL7)]. Immersion tests for Al 2011 have also been carried out in 1 wt.% and 5 wt.% solutions of 1-ethyl,3-methylimidazolium tetrafluoroborate (IL1) in water. No corrosion of Al 2011 by neat ILs is observed. The highest corrosion rate for Al 2011 in water is observed in the presence of a 5 wt.% IL1 due to hydrolysis of the anion with hydrogen evolution and formation of aluminium fluoride. Erosion-corrosion processes have been studied for three aluminium alloys (Al 2011, Al 6061 and Al 7075) in a 90 wt.% IL1 solution in water in the presence of α-alumina particles. The erosion-corrosion rates are around 0.2 mm/year or lower, and increase with increasing copper content to give a corrosion resistance order of Al 6061 > Al 7075 > Al 2011. Results are discussed on the basis of scanning electron microscopy (SEM) observations, energy dispersive spectroscopy (EDS) analysis, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) determinations.     

Thermodynamic properties of some ionic liquids using a simple equation of state

In this work, we have used a simple equation of state (EoS) to predict the density and other thermodynamic properties such as isobaric expansion coefficient, α_P , isothermal compressibility, κ_T, and internal pressure, P_i, for nine ionic liquids including trihexyl (tetradecyl) phosphonium chloride ([(C₆H₁₃)₃P(C₁₄H₂₉)][Cl]), trihexyl (tetradecyl) phosphonium acetate ([(C₆H₁₃)₃P(C₁₄H₂₉)][Ac]), trihexyl (tetradecyl) phosphonium bis {(trifluoromethyl) sulfonyl} amide ([(C₆H₁₃)₃P(C₁₄H₂₉)][NTf₂]), 1-butyl-3-methylimidazolium bis {(trifluoromethyl) sulfonyl} amide ([bmim][NTf₂]), 1-hexyl-3-methylimidazolium bis {(trifluoromethyl) sulfonyl} amide ([hmim][NTf₂]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-butyl-3-octylimidazolium tetrafluoroborate ([omim][BF₄]), 1-butyl-3-octylimidazolium hexafluorophosphate ([omim][PF₆]), and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) at different temperatures and pressures. A wide comparison with experimental and literature data has been made. The results show that this EoS can be used to reproduce and predict different thermodynamic properties of ionic liquids within experimental errors.     

Influence of ionic liquids on the surface properties of poplar veneers

In this paper, the influence of four types of imidazolium-based ionic liquids (ILs) on the surface properties of common aspen (Populus tremula) veneers has been studied by using contact angle, electrical conductivity and Fourier transform infrared spectroscopy analysis. The measurements showed that wood wettabillity is increased by IL treatment. The electrical conductivities of treated wood were in the 0.5-1 mS/cm range, higher than the ones reported in the reference literature. It has been determined that the ILs decrease the crystallinity and improve the flexibility of the cellulose matrix. It has been determined by photographic image analysis that the surface roughness of the IL treated veneers decreases in comparison with the untreated samples.     

新型BrФnsted酸性离子液体的合成与表征

制备了五种对水稳定性好、带-SO3H官能团的磺酸类BrФnsted酸离子液体,用核磁共振(NMR)、红外光谱(IR)、电喷雾质谱(ESI-MS)、热重分析(TG)等表征手段对制备的离子液体进行了表征。结果表明,制备的离子液体与预期设计的结构一致,离子液体纯度大于95%;热重分析发现离子液体具有高的热稳定性和较宽的液态范围,其分解温度均高于300℃;五种离子液体均存在四种离子存在形式,H 可以单独以离子形式存在,并不是通常所认为的仅有两种离子存在形式。另外,研究了离子液体在常用溶剂中的溶解性,发现制备的离子液体易溶于水、甲醇,不溶于乙醚、甲苯和乙酸乙酯。     

Synthesis of aryl azides: a probe reaction to study the synergetic action of ultrasounds and ionic liquids

The combined effect of ultrasounds and ionic liquids was used to perform the synthesis of aryl azides by nucleophilic aromatic substitution in ionic liquid/[1-butyl-3-methylimidazolium][N₃] binary mixtures. The ultrasounds efficiency was analyzed as a function of the substrate and of the ionic liquid structure. In the first case, both 6π and 10π electrons aryl halides were considered. As far as the ionic liquid structure is concerned, both aromatic and aliphatic ionic liquids were taken into account. Among aromatic cations, the effects due to different ability in giving hydrogen bond or π-π interactions were considered. The use of a geminal ionic liquid having an aromatic spacer was examined too.On the whole, collected data evidence an activating effect on the target reaction by the combined use of ultrasounds and ionic liquids. The structural order degree of the ionic liquid seems to be the main factor affecting the ultrasounds efficiency. Furthermore, the effects due to changes in the anion structure seem to be more significant than those due to changes in the cation structure.     

Spectroscopic investigation on the effect of pairing anions in imidazolium-based ionic liquids on the J-aggregation of meso-tetrakis-(4-sulfonatophenyl)porphyrin in aqueous solution

The effect of pairing anions in imidazolium-based ionic liquids (ILs) on the J-aggregation of meso-tetrakis-(4-sulfonatophenyl)porphyrin (TPPS) is investigated in aqueous solutions by the spectroscopic methods. The ILs used herein possess similar cations but different pairing anions, tetrafluoroborate (BF₄⁻) and p-toluenesulfonate (TS⁻). The results from absorption and fluorescence spectra indicate that the J-aggregation is mainly regulated by anionic species. The J-aggregation of TPPS is initially promoted with the increase of 1-butyl-3-methylimidazolium tetrafluoroborate/1-ethyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄/EMIMBF₄) until 0.10/0.40 mol/L and subsequently weakened slightly with further increase of BMIMBF₄/EMIMBF₄ concentration. However, the J-aggregation of TPPS hardly occurs in the tested concentration range of 1-butyl-3-methylimidazolium-tosylate/1-ethyl-3-methylimidazolium-tosylate (BMIMTS/EMIMTS). Furthermore, obvious redshifts in both absorption and fluorescence spectra of TPPS are observed with progressive addition of BMIMTS/EMIMTS. TPPS induces proton chemical shifts of BMIMBF₄/EMIMBF₄ and BMIMTS/EMIMTS to shift downfield and upfield, respectively. So it can be concluded that ILs with simple pairing anion BF₄⁻ promote the J-aggregation of TPPS by charge equilibrium, while ILs with pairing anion TS⁻ inhibit the J-aggregation of TPPS by the π-π and hydrophobic interaction.     

Applying electrohydrodynamic atomization to enhance mass transfer of metal salts from an aqueous phase towards ionic liquids

In this work a two coaxial nozzles configuration is used to investigate whether electro hydrodynamic atomization of an ionic liquid in combination with an aqueous metal salt solution could enhance the removal of metal salts. The technique was evaluated for the removal of manganese (II), cobalt (II) calcium and sodium chloride. Good metal salt extraction was observed for the water-presaturated ionic liquid, tetraoctylammonium oleate, at an applied electrical potential of 5 kV, which was slightly lower compared to mechanical mixing, but a higher separation factor was obtained between the transition metals and the alkali and earth alkali metals.