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.     

Mesophilic alcohol dehydrogenase behavior in imidazolium based ionic liquids

The use of ionic liquids to replace organic solvents in biocatalytic processes has recently gained much attention. Despite the wide applications of oxidoreductases, there are few reports of their catalyzed reaction in ionic liquid. We have investigated the influence of four water miscible ionic liquids on the activity, stability and structure of the mesophilic alcohol dehydrogenase from yeast. Upon changes in ionic liquids concentration, both activity and stability of the enzyme were affected. As the concentration of ionic liquids increased, K_m increased while k_cat decreased. Associated conformational changes caused by ILs (150 mM) were monitored using fluorescence technique. Finally, the effects of ILs cations and anions on the enzyme activity and stability in aqueous IL mixtures were discussed.     

Studies on electrowetting of room temperature ionic liquids

This paper reports experimental investigations on the electrowetting behavior of ionic liquids in comparison with aqueous electrolytes, which is one of the important research topics in optofluidics. The effect of applied voltage on the contact angle is reported in detail. In addition, the liquid–solid material interfacial tension and the thickness of insulating layer are estimated under certain conditions. Related conclusions are valuable in the field of future electrowetting applications.     

Effect of monocationic ionic liquids as electrolyte additives on the electrochemical and thermal properties of Li-ion batteries

The conventional electrolyte system has been compared with the ionic liquid (IL) additive containing electrolyte system at room temperature as well as elevated temperature. In this work, two types of monocationic ILs such as 1-butyl-3-methylpyrrolidinium hexafluorophosphate (Pyr IL) and 1-ethyl-3-methylimidazolium hexafluorophosphate (IMI IL) are added as an additive at two different weight ratios in 1.15 M LiPF₆ (EC/EMC = 3/7 v/v) electrolyte solution, the structural, electrochemical and thermal characteristics of LiNi_0.80Co_0.15Al_0.05O₂ (NCA)/carbon full-cell in different electrolyte formulations have been reconnoitered. X-ray diffraction (XRD) studies have proved that IL as an electrolyte additive does not alter the structural stability of cathode materials after cycling. Under room temperature, Pyr IL additives at 1 wt% and 3 wt% deliver better cycleability than others, with the retention ratios of 93.62% and 92.8%, respectively. At elevated temperature, only 1 wt% Pyr IL additive is giving stable capacity retention ratio of 80.74%. Ionic conductivity and self-extinguishing time (SET) values are increasing with respect to the amount of additive added to the electrolyte. Thermal studies reveal that 3 wt% Pyr IL is favorable regarding the safety of the battery as it shows shifting of peak to higher temperature of 272.10 °C. Among the IL additives evaluated in this study, addition of 1 wt% Pyr IL is the most desirable additive for achieving the best cycling performance as well as thermal behavior of Li-ion batteries.     

Modelling interfacial properties of ionic liquids with ePC-SAFT combined with density gradient theory

Highlights

• Combination of ePC-SAFT with density gradient theory

• Calculation of interfacial properties of pure ILs in broad temperature range

• Quantitative predictions of surface tensions for ILs not used in κ parameter fitting

     

Synergic effects of ultrasound and ionic liquids on fluconazole emulsion

The aim of this work was to evaluate the influence of US on the properties of the fluconazole emulsions prepared using imidazolium-based ILs ([C_n C₁im]Br). The effects of the preparation method (mechanical stirring or US), US amplitude, alkyl chain length (of [C₁₂C₁im]Br or [C₁₆C₁im]Br), and IL concentration on the physicochemical properties were evaluated. Properties such as droplet size, span index, morphology, viscosity encapsulation efficiency, and drug release profile were determined. The results showed that US-prepared emulsions had a smaller droplet size and smaller polydispersity (Span) than those prepared by mechanical stirring. Additionally, the results showed that emulsions prepared with [C₁₆C₁im]Br and US had spherical shapes and increased stability compared to emulsions prepared by MS, and also depended on the IL concentration. The emulsion prepared by US at 40% amplitude had increased encapsulation efficiency. US provided a decrease in the viscosity of emulsions containing [C₁₂C₁im]Br; however, in general, all emulsions had viscosity close to that of water. Emulsions containing [C₁₆C₁im]Br had the lowest viscosities of all the emulsions. The emulsions containing the IL [C₁₆C₁im]Br had more controlled release and a lower cumulative percentage of drug release. The IL concentration required to prepare these emulsions was lower than the amount of conventional surfactant required, which highlights the potential synergic effects of ILs and US in preparing emulsions of hydrophobic drugs.     

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.     

Electronic structures of imidazolium-based ionic liquids

Electronic structures of ionic liquids formed by 1-buthyl-3-alkylimidazolium ion [C_nmim]⁺ (n = 4 and 8) with various inorganic and organic anions have been investigated by ultraviolet photoemission, X-ray photoemission, inverse photoemission and soft X-ray emission spectroscopies (SXES). The comparison of the calculated density of states with the observed spectra revealed that the molecular orbital energies of these ionic liquids are significantly affected by the electrostatic Madelung potential among the ions. The SXES results clearly show that the both highest occupied and lowest unoccupied states of [C₄mim]⁺PF₆⁻ are derived from the cation as a result of strong Madelung potential. On the other hand, the SXES results show the valence electronic structures of ionic liquids with larger anion molecules, [C_nmim]⁺Tf₂N⁻ and [C_nmim]⁺OTf⁻ are contributed from the both cation and anion.     

Thermodynamic properties of the mixtures of some ionic liquids with alcohols using a simple equation of state

In the present work, we have used a simple equation of state called the GMA EoS to calculate the density of three ionic liquid mixtures including 1-butyl-3-methylimidazolum hexafluorophosphate, [BMIM] [PF₆] + methanol, 1-butyl-3-methylimidazolum tetrafluoroborate, [BMIM] [BF₄] + methanol, and [BMIM] [BF₄] + ethanol at different temperatures, pressures, and compositions. The isothermal compressibility, excess molar volumes, and excess Gibbs molar energy of these mixtures have been computed using this equation of state. The values of statistical parameters show that the GMA EoS can predict these thermodynamic properties very well within the experimental errors. The results show that isothermal compressibility of ionic liquids is lower than alcohols and the effect of temperature and pressure on the isothermal compressibility of ionic liquids is lower than alcohols. The excess molar volumes and excess molar Gibbs energy for these ionic liquid mixtures with alcohols are all negative at various temperatures and pressures over the whole composition range. The results have been interpreted in terms of intermolecular interactions and structural factors of the ionic liquids and alcohols.     

Synthesis of ZnO nanostructures with controlled morphology and size in ionic liquids

Nanostructured ZnO has been synthesized by a hydrothermal route, using different ionic liquids (ILs) as the morphology templates. The morphology of ZnO changes from rod-like to star-like and flower-like in different ILs. A 3D nano/micro structure ZnO with unique flower-like morphology has been synthesized via the assembly of dicationic IL and [Zn(OH)₄]²⁻. The flower-like pattern was obtained in the presence of IL 1. The flower-like ZnO structure has a hexagonal prism, with a hexagonal pyramid on the tip, and diameter of ~444 nm. While the ZnO prepared in IL 2, shows uniform rod-like shape with a diameter of 91 nm, star-like morphology consisting of nanorods with diameter of ~109 nm was formed in IL 3. The XRD, SEM, and PL spectra have been employed for characterization of the synthesized ZnO nano structures.     

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.     

Electroreduction of N-methylphthalimide in room temperature ionic liquids under insonated and silent conditions

The selective electroreduction N-methylphthalimide to 3-hydroxy-2-methyl-isoindolin-1-one has been performed in ionic liquids using phenol as a proton donor under silent and ultrasonic conditions. A significant increase in the rate of electroreduction is shown using ultrasonic activation and in addition high current efficiencies were observed. Some decomposition of the ionic liquid was found to have occurred under exposure to ultrasound.     

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.     

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.     

Study of tribochemical decomposition of ionic liquids on a nascent steel surface

Tribological properties and the decomposition process of ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide) on a nascent surface of bearing steel 52100 were investigated by a ball-on-disk friction tester in a vacuum chamber equipped with a quadrupole mass spectrometer (Q-MS). Ionic liquids exhibited better tribological properties than synthetic hydrocarbon oil (multialkylated cyclopentane (MAC)) in high vacuum conditions. The induction period for decomposition of MAC was about 10 km, while no obvious gaseous products were observed for ionic liquids even after a sliding distance of 22 km under the same mechanical conditions. The mass spectra indicated that both the anionic and cationic moieties of ionic liquids decomposed on the nascent steel surface during friction processes. The cationic moiety with a longer alkyl chain was more difficult to decompose on the nascent steel surface than that with a shorter alkyl chain. XPS analysis revealed that the tribofilm formed by ionic liquid was mainly composed of FeF₂ and FeS, which deactivated the nascent surface. As a result, desorption rate of gaseous products decreased appreciably comparing with MAC. The critical load for the mechanical activation of the decomposition correspondingly increased from 1.1 N of MAC to 8 N of ionic liquids.     

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.     

Thermal behaviour of two room-temperature ionic liquids containing the methylimidazolium cation

We have investigated the glass transition relaxation of two room-temperature ionic liquids using Modulated Temperature Differential Scanning Calorimetry (MTDSC). Furthermore, conventional DSC was used to clarify their crystallisation behaviour. One of the liquids avoids crystallisation, while the other shows cold crystallisation. A step-by-step temperature scanning experimental procedure was used to analyse in detail the thermal behaviour of the latter in the crystallisation and melting temperature regions. The existence of polymorphism is discussed.     

Theoretical investigation of imidazolium based ionic liquid/alcohol mixture: a molecular dynamic simulation

In this work, molecular dynamic simulation of the mixture of imidazolium based ionic liquids with alcohols is implemented in order to investigate mixing excess properties and some structural and physical properties of the mixture. Excess volumes and enthalpies are evaluated for 11 different mole fractions of ionic liquids at each 0.1, in the range of 0 to 1. Radial distribution function, cohesive energy density, potential of mean force, solvation energy, and diffusion coefficient are reported and analysed. The effects of the cationic alkyl chain length, in comparison with changes of the anions, on these properties are reported. Results reveal that the methanol molecule participates with its hydrophilic characteristics in the mixing process and tends to aggregate around anion part of the ionic liquids, especially in the case of Cl.     

Ionic liquid analogous formed from magnesium chloride hexahydrate and its physico-chemical properties

In this paper, a homogeneous, colorless ionic liquid analogous containing choline chloride and magnesium chloride hexahydrate is reported. The structure of the ionic liquid analogous is preliminarily investigated by Fourier transform infrared spectroscopy (FTIR). It is shown that the magnesium chloride hexahydrate bonds via hydrogen bonds with choline chloride. The physico-chemical properties of the ionic liquid analogous such as melting point, viscosity, conductivity and density are measured as a function of temperature and composition. A straight line equation is used to fit the density data while the Arrhenius equation is used to fit both viscosity and conductivity. The thermal expansion coefficients (r), the molar Gibbs energy of activation (ΔG*) for viscous flow, the molar enthalpy of activation (ΔH*) and the molar entropy of activation (ΔS*) for viscous flow have been calculated.