Properties Of Imidazolium-based Ionic Liquids Research Articles

Vibrational Spectra Simulations in Amino Acid-Based Imidazolium Ionic Liquids.

We present maximally localized Wannier functions and Voronoi tessellation to obtain dipole moment distributions for vibrational spectra in several important ionic liquids calculated by using ab initio molecular dynamics simulations. IR and Raman spectra of various imidazolium-based ionic liquids (ILs) paired with six amino acid anions are shown herein. For IR spectra, two approaches (Wannier and Voronoi) are in agreement with respect to the relative intensities and the overall shapes for the main peaks. Under Raman spectra, the polarizability of the covalent bonds is shown to affect the strength of the Raman scattering signal. The advantage of the Voronoi tessellation method, being that it does not have strong spikes in its time development, is demonstrated by the comparison of two theoretical methods (Wannier and Voronoi) with experimental data. We analyze the errors between theoretical and experimental spectroscopic data, with the Voronoi method shown to accurately reproduce experimental values. In addition, theoretical spectroscopy shows the ability to accurately separate components of a mixture. The combination of theoretical and experimental methods is utilized to understand the spectroscopic properties of amino acid-based imidazolium ILs.

Hydrogen-Bonded Complexes in Binary Mixture of Imidazolium-Based Ionic Liquids with Organic Solvents.

Though local structures in ionic liquids are dominated by strong Coulomb forces, directional hydrogen bonds can also influence the physicochemical properties of imidazolium-based ionic liquids. In particular, the C-2 position of the imidazolium cation is acidic and can bind with suitable hydrogen bond acceptor sites of molecular solvents dissolved in imidazolium-based ionic liquids. In this report, we identify hydrogen-bonded microenvironments of the model ionic liquid, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate, and the changes that occur when molecular solvents are dissolved in it by using a C-D infrared reporter at the C-2 position of the cation. Our linear and nonlinear infrared experiments, along with computational studies, indicate that the molecular solvent dimethyl sulfoxide can form strong hydrogen-bonded dimers with the cation of the ionic liquid at the C-2 position. In contrast, acetone, which is also a hydrogen bond acceptor similar to dimethyl sulfoxide, does not show evidence of cation-solvent hydrogen-bonded conformers at the C-2 position. The outcome of our study on a broad scale strengthens the importance of cation-solute interactions in ionic liquids.

Study on extract-pyrolysis cascading utilization characteristics of typical biomass using imidazolium-based ionic liquids

As the main utilization method of biomass, direct pyrolysis destroyed high value-added constituents. Extract-pyrolysis cascading utilization technical was applied in two typical biomasses: chlorella (CH) and pine sawdust (PS). Four imidazolium-based ionic liquids (ILs) were chosen as the extractants, and obtained higher extraction yield for CH than PS. Among them, BmimCl (1-Butyl-3-methylimidazolium chloride) obtained highest extraction yield for CH and PS of 72.73% and 20.58%. Selected ILs exhibited strong extraction abilities of oxygen-containing compounds for both CH and PS and nitrogen-containing compounds for CH. Compared with direct pyrolysis, gas and char yields of CH and PS had obvious decrease and the liquid phase products yields increased with more diverse composition especially phenolic compounds. The liquid phase products yield of PS and CH increased by 27.15%, 37.80% and 61.20%, 70.82% using BmimHSO4 (1-Butyl-3-methylimidazolium hydrogensulfate) and BmimCl. The extract-pyrolysis characteristics of CH and PS were obtained through the comparison of gas–liquid-solid products composition and distribution, and they depend on the structure of biomass and the physical–chemical properties of ILs. Extract-pyrolysis utilization approach has potential to realize clean and high-value utilization of biomass, and more valuable liquid products can be obtained.

Role of C2 methylation and anion type on the physicochemical and thermal properties of imidazolium-based ionic liquids

This study focused on the effects of methylation and different anions (Br − and Cl − ) on the physicochemical and thermal properties of [C 16 MIM]X and [C 16 MMIM]X, belonging to the imidazolium-based ionic liquid (IL) family. The effect of methylation on the transmittance in the fingerprint region of the Fourier transform infrared (FT-IR) spectrum was observed as a blue shift, and a new peak associated with the C-N stretching bond was obtained. In contrast, in the functional group region, the frequency shift was related to the change in the vibrational mode from C2-H-X to C2-methyl-X. In general, methylation resulted in an increase in decomposition temperature, an increase in melting temperature, and a decrease in melting enthalpy, leading to a reduction in entropy. The trends observed for the decomposition temperature, melting temperature, and melting enthalpy with different anions depended on the strength of the Brønsted acids and hydrogen bonds of the Br − and Cl − based anions. The thermal conductivity of the methylated ILs increased with an increase in temperature. In contrast, for the non-methylated (protonated) ILs, the thermal conductivity of [C 16 MIM]Br decreased with an increase in temperature, while the opposite trend was observed for [C 16 MIM]Cl. The data were compared with those of the short alkyl chain and weakly coordinating anion of NTf 2 . The analysis was performed considering different phases, the prominent role and different behaviour in the hydrogen bonding at the C2 position of the imidazolium ring upon methylation, and the significant change in viscosity, which can influence the IL structure.

Imidazolium based ionic liquids as green corrosion inhibitors against corrosion of mild steel in acidic media

Ionic liquids are compounds that consist entirely of ions. Since the last decade, ionic liquids have evolved as effective corrosion inhibitors. Ionic liquids are extensively used as potent corrosion inhibitors against metals and alloys because of their high solubility, low toxicity, low melting point, high polarity, and very high stability to thermal and chemical processes. This review would focus on the excellent inhibition properties of imidazolium-based ionic liquids, as well as the different factors that affect the inhibition efficacy of these compounds, such as the effect of chain length, molecular surface area, and position of substituents attached to the imidazolium ring, and so on. This article discusses the recently analyzed imidazolium-based ionic liquids and their inhibition mechanisms as studied by employing several techniques such as Potentiodynamic polarization, Weight loss, electrochemical impedance spectroscopy, Atomic force microscopy (AFM), Scanning electron microscopy (SEM), Density functional theory (DFT) studies, Molecular dynamics simulations and so on.

Temperature and Composition Dependence of the Thermodynamic Properties of an Aqueous Solution of 1-Ethyl-3-methylimidazolium Formate and 1-Ethyl-3-methylimidazolium Acetate

New experimental data on the thermodynamic properties of imidazolium-based ionic liquids (ILs) and {IL + water} solutions are presented. The isothermal (vapor + liquid) phase equilibrium (VLE) and the density of binary mixtures composed of 1-ethyl-3-methylimidazolium formate, [EMIM][HCOO], or 1-ethyl-3-methylimidazolium acetate, [EMIM][CH3COO], and water are demonstrated. The experimental data were measured at temperatures from 298.15 to 348.15 K over a wide IL mole fraction under ambient pressure. Both ILs were delivered by IoLiTec, and the water content was determined by the Karl–Fischer titration technique. The thermophysical properties of the pure ILs, that is, glass-transition temperature, heat capacity at glass-transition change, and the temperature and enthalpy of melting, were determined by differential scanning calorimetry technique. The VLE has been measured by an ebulliometric method at temperatures from 338.15 to 368.15 K and pressures up to 85 kPa. The experimental VLE data were tested for thermodynamic consistency using the Van Ness test. The nonrandom two-liquid model equation was used to correlate the experimental VLE data. The density of the tested aqueous solution has been measured as a function of IL’s mole fraction over a wide temperature range. The empirical equations were applied for density data correlation. From the experimental density data for the {[EMIM][CH3COO] (1) + water (2)} system, the excess molar volumes were determined and correlated using the Redlich–Kister equation.

Prediction of the Liquid-Liquid Extraction Properties of Imidazolium-Based Ionic Liquids for the Extraction of Aromatics from Aliphatics.

Liquid-liquid extraction (LLE) is an important technique to separate aromatics from aliphatics since these compounds have very similar boiling points and cannot be separated by distillation. Ionic liquids (ILs) are considered as potential extractants to extract aromatics from aliphatics. In this paper, molecular dynamics (MD) simulations were used to predict the extraction property (i.e., capacity and selectivity) of ILs for the LLE of aromatics from aliphatics. The extraction properties of seven different ILs including [C2mim][Tf2N], [C2mim][TFO], [C2mim][SCN], [C2mim][DCA], [C2mim][TCM], [C4mim][Tf2N], and [C8mim][Tf2N] were investigated. Results show that ILs with shorter alkyl chain cations and [Tf2N]- anion exhibit better extraction efficiency than other ILs, which is in agreement with previously reported experimental data on the extraction of toluene from aliphatics and further validated the reliability of the proposed model. The binding energies between ILs and organic molecules were calculated by the density functional theory, which help explain the different extraction behaviors of different ILs. The symmetry-adapted perturbation theory analysis was performed to further understand the interaction mechanisms between ILs and organics. Our study shows that the [Tf2N]- anion also has the best extraction capability for heavier aromatics (o-xylene, m-xylene, and p-xylene) from common aliphatics (heptane and octane). The MD modeling approach can be a low-cost in silico tool for the high-throughput fast screening of ILs for the LLE of aromatics from aliphatics.

Imidazolium‐based poly(ionic liquid)s for demulsification of water in crude oil emulsions

Imidazolium‐based ionic liquids (ILs) and their corresponding poly(ionic liquid)s (PILs) as powerful demulsifiers for water separation from the crude oil emulsions were used. Vinyl imidazolium‐based ILs were prepared and then polymerized according to the free radical homo‐polymerization. NMR and FT‐IR analyses confirmed the successful synthesis of ILs and their corresponding polymers. Demulsifying properties of different synthetic ILs, including [C12‐VIM][Br], [C10‐VIM][Br], [C8‐VIM][Br], [C6‐VIM][Br], [C4‐VIM][Br], and [Benzyl‐VIM][Br]) and their analogous poly(ionic liquid)s were evaluated and compared with each other. The influence of the important parameters on the emulsion breaking such as demulsifier concentration, the alkyl chain length of the synthesized demulsifiers, and the operating factors such as the stirring rate, stirring time, and temperature were investigated through the bottle test. Maximum dehydration efficiencies around 99.2% for [C12‐VIM][Br] at 400 ppm and 100% for P[C12‐VIM][Br] at 50 ppm were achieved after 4 hours at 70°C, 15 minutes stirring time, and 800 rpm stirring rate. After demulsification of the crude oil emulsions, the interfacial tension decreased from 22.18 ± 0.1 to 0.83 ± 0.2 mN/m for [C12‐VIM][Br] and from 20.18 ± 0.2 to 0.70 ± 0.2 mN/m for P[C12‐VIM][Br]. The average diameter of the water droplets increased from 2‐10 ± 0.63 to 30‐140 ± 0.51 for [C12‐VIM][Br] within 20 minutes. In addition, the residual water content decreased from 20% to 0.04% for [C12‐VIM][Br] within 24 hours.

Temperature-dependent spectroscopic properties of imidazolium-based Ionic Liquids in the 100 MHz to 10 GHz microwave region

Microwave spectroscopic properties of imidazolium-based ionic liquids has been investigated in the 100 MHz to 10 GHz range over a range of temperature between 25 oC and 125 oC for characterising the dielectric and loss factor properties.

Synthesis and characterization of physicochemical properties of imidazolium-based ionic liquids and their application for simultaneous determination of sulfur compounds

Three types of imidazolium-based ionic liquids (IMILs) were synthesized and characterized by 13C and 1H NMR, FT-IR, and elemental analysis. Thermal stability and physicochemical properties of prepared IMILs were measured in the temperature range of 283.15 to 363.15 K. The physicochemical results revealed the entirely temperature-dependent properties and quietly decreasing through increasing the temperature. Electrochemical studies of the IMILs were also performed at the surface of screen-printed electrode cells. Consideration of these properties and determining the unique abilities of IMILs will help researchers through modern applications like liquid-liquid extraction, particular tasks of scavenging and removal of hydrogen sulfide and thiols from petroleum matrices.

Functionalized imidazolium-based ionic liquids: biological activity evaluation, toxicity screening, spectroscopic, and molecular docking studies

A series of long-chain imidazolium-based ionic liquids (ILs) 1-dodecyl-3-methylimidazolium chloride (1), 1,3-bis(octyloxycarbonylmethyl)imidazolium chloride (2) and 1-dodecyloxycarbonylmethyl-3-methyloxycarbonylmethylimidazolium chloride (3), were synthesized and evaluated as antimicrobials against a wide range of bacteria and fungi. Toxicological risks of selected compounds were assessed using the biomodels of various organizational and functional levels. All compounds demonstrated significant antibacterial and antifungal activity. The toxicity results indicate that ILs containing an ester functional group in the alkyl side chain exhibited much lower toxicity to D. magna and acetylcholinesterase inhibition than ILs with long alkyl chain without polar substituents, while toxicity toward Danio rerio was on a par. The HSA-binding properties of ILs have been investigated by FT-IR spectroscopy technique and the evidences have suggested that the test compounds could induce the protein unfolding and changes in the secondary structure of HSA. The docking studies were carried out to provide structural insights of the ILs–HSA-binding interactions. The docked compounds exhibit a high binding affinity to HSA and the hydrogen bonding, hydrophobic and electrostatic interactions played a major role in the process. ILs 2 and 3 may be perspective for further investigation as potential low-toxic biocides with high antimicrobial activity against reference and clinical multidrug-resistant strains.

Wetting behavior of aqueous 1-alkyl-3-methylimidazolium tetrafluoroborate {[Cn MIM][BF4] (n = 2, 4, 6)} on graphite surface

Herein, molecular dynamics simulations have been conducted to investigate the effect of cation chain length on the wetting and interfacial properties of aqueous imidazolium-based ionic liquids (ILs) consisting of 1-ethyl-3-methylimidazolium [EMIM], 1-butyl-3-methylimidazolium [BMIM], and 1-hexyl-3-methylimidazolium [HMIM] cations with common tetrafluoroborate [BF4] anions on a graphite surface in the IL concentration range of 10–50 wt%. The difference between the contact angles of aqueous [EMIM][BF4] and [BMIM][BF4] droplets is very small regardless of the IL content. However, a noticeable reduction in the contact angle is observed for the IL with a longer alkyl chain [HMIM][BF4] at high IL concentrations. Furthermore, interfacial tensions and works of adhesion are calculated to quantify the wettability of the studied ILs; as a result, lower works of adhesion are obtained for the longer alkyl chain compounds (Sali et al., 2017). Droplet characteristics near the surface are obtained from two-dimensional density contours and orientation order parameters. The majority of IL molecules are located near the solid–liquid interface in all the studied cases. However, the [BMIM][BF4] and [HMIM][BF4] ILs with longer alkyl chains are also detected at the liquid–vapor interface. Finally, IL interactions with water molecules through hydrogen bonding are investigated at various concentrations. The obtained interfacial tensions are in good agreement with the experimental values reported in the literature. The results of this study can help elucidate the wetting and interfacial properties of aqueous imidazolium-based ILs.

An inspection of the dispersive properties of imidazolium-based ionic liquids in the Vis-NIR

In this work, the refractive index dependence on the wavelength of 20 ionic liquids is characterised by spectrally resolved white-light interferometry in a spectral interval comprising a range of wavelengths from 400 to 1000 nm at different temperatures between 298.15 and 323.15 K. With these data and using a refractive index model based on a single resonance Sellmeier equation, we calculate the Abbe number, group index, group velocity dispersion, and dispersion of the thermo-optic coefficient for each liquid. Using the Lorentz–Lorenz approach and density data, we demonstrate (from the empirical results) the linear variation of the molar volume and molar refraction with the number of carbons in the alkyl chain. Further, we confirm that this linear relation can be used to predict the refractive index of liquids of the same family provided the addition of CH2 groups does not lead to anisotropies in the refractive index.

Effect of the chain lengthening on transport properties of imidazolium-based ionic liquids

The objective of this work is to study the effect of the lengthening of the linear alkyl chain of the imidazolium cation on some transport properties. We focused on hydrophobic ionic liquids based on bis(trifluoromethanesulfonyl)imide anion. Among the different properties, we measured at the viscosity and ionic conductivity of four different 1-alkyl-3-methylimidazolium ionic liquid in the temperature range between 293 and 333K. Thus, Electrochemical windows of these ionic liquids and the diffusion coefficient of ferrocenemethanol (FcMeOH) in the four ionic liquids were studied using cyclic voltammetry at 298K. The FcMeOH diffusion coefficient was found to be higher in shorter alkyl chain ionic liquids.

Effect of alkyl chain length on the wetting behavior of imidazolium based ionic liquids: A molecular dynamics study

Molecular dynamics (MD) simulations are performed to investigate the wetting behavior of imidazolium-based ionic liquids (ILs), which mainly consist of an imidazolium ring with a flexible alkyl chain attachment. The length of the alkyl chain can be easily manipulated to modulate the wetting properties of the ILs. To understand the role of the alkyl chain, we investigate the wetting behavior of two room-temperature ionic liquids (RTILs), 1,3-dimethylimidazolium tetra-fluoroborate [DMIM][BF4] and 1-propyl-3-methylimidazolium tetra-fluoroborate [PrMIM][BF4], on a graphite surface. Furthermore, the effects of the droplet size and temperature on the contact angle of the IL droplets are investigated. The wetting behaviors of both IL droplets are characterized using a density profile and orientation order parameter profile along the axis normal to the surface. The length of the alkyl chain is found to be crucial for modulating the wetting properties of the ILs. With an increase in the length of the alkyl chain, the contact angle of the droplet decreases, which is also in line with experimental results [1,2]. The wetting of the IL droplets strongly depends on the temperature and the relative fluid-fluid and fluid-substrate interactions. With the increase in temperature, the contact angle of the IL droplet decreases, resulting in the formation of a single layer film at a high temperature. In addition, the behavior of the contact angle of the IL droplet is analyzed through the surface tension as well as the graphite-IL interfacial tension. Furthermore, considering the anisotropic properties of the imidazolium-based ILs, we calculate the contact angles for cylindrical filaments (2D) on the graphite surface and compare the obtained values with the contact angle obtained from the spherical droplet (3D). The contact angle of the cylindrical droplet is found to have a negligible system size effect as compared to the case with the spherical droplet.

Improvement of the properties of 1-ethyl-3-methylimidazolium acetate using organic solvents for biofuel process

Imidazolium-based ionic liquids (ILs) are widely used in bio-chemical processes for biofuel production. Ionic liquids always possess high viscosity that would impede the dissolution process of biomass and decrease the transfer rate. In this work, four organic solvents of N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and pyridine (PYR) are chosen as the diluent to improve the properties of IL, namely, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) that shows promise for biofuel process in recent studies. The experimental density and viscosity of the binary mixtures are determined to quantitatively evaluate the effects of organic solvents on IL. The thermal expansion coefficient is derived from the experimental data. The excess properties are calculated to study the molecular interaction.

Effects of C(2) Methylation on Thermal Behavior and Interionic Interactions in Imidazolium-Based Ionic Liquids with Highly Symmetric Anions

The chemical and physical properties of imidazolium-based ionic liquids are determined by the interactions between the counter-ions. The C(2) position plays an important role in these interactions, as it represents the predominant site for interionic hydrogen bonding. This study shows that the directional hydrogen bonds between highly symmetrical anions (iodide, tetrafluoroborate, hexafluorophosphate) and the C(2)-H group of the 1-methyl-3-propylimidazolium cation determine the molecular and macroscopic behavior in terms of the thermal properties. Upon replacing the C(2) proton by a methyl group, the anion repositions itself at the C(4)/(5) moiety, where it forms a new hydrogen bond, apparently with only one of the two CH groups. In addition, the larger the anion is in diameter, the more likely it will establish further interactions with other parts of the cation, such as the propyl chain.

Influence of the N-3 alkyl chain length on improving inhibition properties of imidazolium-based ionic liquids on copper corrosion

1-butyl-3-ethylimidazolium bromide ionic liquid, [beim]Br, was studied experimentally and theoretically as a potential inhibitor of copper corrosion in acidic media (pH = 3) by dc polarization, quartz crystal microbalance (QCM), scanning electron microscopy (SEM) and density functional theory (DFT). This ionic liquid is selected to study an effect of the alkyl chain length at the position N-3, since so far only ionic liquids with different alkyl substituents at the position N-1 are investigated. Improved inhibitory properties of the investigated ionic liquid against corrosion of copper in acidic solution at the given conditions are confirmed comparing to corresponding 1-butyl-3-methylimidazolium bromide ionic liquid. It is found that [beim]Br acts as a cathodic corrosion inhibitor, whereby its effectiveness depends on the applied concentration. The inhibitory effect of the studied ionic liquid (IL) was achieved through quick and spontaneous adsorption on the copper surface following the Langmuir's adsorption isotherm. Results obtained by SEM showed that copper protection is achieved through the less damaged copper surface in the presence of inhibitor. Applying DFT calculations, it is found that interactions with the metal surface occur by donating electron from the Br− anion to the copper. Based on the obtained Fukui functions influence of the inductive effect of ethyl/methyl group on the inhibitory activity is also discussed.

Temperature Dependence of Volumetric and Dynamic Properties of Imidazolium-Based Ionic Liquids.

Atomistically detailed molecular dynamics simulations were used to investigate the temperature dependence of the specific volume, dynamic properties, and viscosity of linear alkyl chain ([CnC1Im][NTf2], n = 3-7) and branched alkyl chain ([(n - 2)mCn-1C1Im][NTf2]) ionic liquids (ILs). The trend of the glass transition temperature (Tg) values obtained in the simulations as a function of the alkyl chain length of cations was similar to the trend seen in experiments. In addition, the system relaxation behavior as determined from the temperature dependence of the diffusion coefficient, rotational relaxation time, and viscosity close to Tg was observed to follow the Vogel-Fulcher-Tammann expression. Furthermore, the reciprocal of the diffusion coefficient of the anion and cation in both linear and branched IL systems showed a linear correlation with viscosity, thus confirming the validity of the Stokes-Einstein relationship for these systems. Similarly, the average rotational relaxation time of the ions was also found to correlate linearly with the viscosity of the ILs over a wide range of temperatures, thereby validating the Debye-Stokes-Einstein relationship for the ILs. These simulation findings suggest that the temperature dependence of the relaxation time of ILs is very similar to that of other glass-forming liquids.

A systematic study on physicochemical and transport properties of imidazolium-based ionic liquids with γ-butyrolactone

Densities, viscosities and electrical conductivities were determined and discussed for γ-butyrolactone (GBL) with 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid ([mmim][NTf2]) binary mixtures as a function of temperature at atmospheric pressure over the whole composition range. From the experimental density data the related excess molar volumes were calculated and fitted using Redlich–Kister’s polynomial equation. The thermal expansion coefficients were also calculated from the acquired experimental density values. Electrical conductivity data were correlated using Casteel–Amis and Arrhenius equations. The influence of viscosity on electrical conductivity was discussed within the scope of Walden rule. Volumetric and transport properties of GBL binary mixtures with selected ionic liquid are compared with available literature data for the corresponding 1-methyl-3-alkylsupstituted imidazolium based ILs.