Imidazolium Ethyl Sulfate Research Articles

Imaging a solvent‐swollen polymer gel network by open liquid transmission electron microscopy

AbstractVisualizing the network of a solvent‐swollen polymer gel remains problematic. To address this challenge, open transmission electron microscopy (TEM) was applied to thin gel films permeated by a nonvolatile ionic liquid. The targeted physical gels were prepared by cooling concentrated solutions of poly(ethylene glycol) in 1‐ethyl‐3‐methyl imidazolium ethyl sulfate [EMIM][EtSO4]. During the cooling, gelation occurred by a frustrated crystallization of the dissolved polymer, leading to a percolated, solvent‐permeated semicrystalline network in which nanoscale polymer crystals acted as crosslinks. Crystalline features ranging from ~5 to ~200 nm were observed, with the visible network strands dominantly consisting of long curvilinear crystallites of ~15–20 nm diameter. Nascent spherulites irregularly decorated the network, creating a complex structural hierarchy that complicated analyses. Lacking diffraction contrast, TEM did not visualize the many disordered, fully solvated PEG chains present in the voids between crystals. Recognizing that a network's three dimensionality is ambiguous when assessed through two‐dimensional microscopy projections, a small gel region was studied by TEM tomography, revealing a nearly isotropic three‐dimensional arrangement of the curvilinear crystallites, which displayed remarkably uniform cylindrical cross sections.

Effect of ionic liquids’ chemistry on their lubrication behaviour under various contact pressures

The promising properties of Ionic Liquids (ILs) such as their low vapour pressure, high thermal stability and high thermal conductivity make them strong candidates to be used as either neat lubricants or additives. The effect of ionic liquids' chemistry on their lubrication behaviour is examined in this study by comparing the performance of five neat ILs, i.e. Ethyl Methyl Imidazolium Ethyl Sulfate (EMIM ESU), Ethyl Methyl Imidazolium Octyl Sulfate (EMIM OSU), Butyl Methyl Imidazolium Octyl Sulfate (BMIM OSU), Ethyl Methyl Imidazolium Ethyl Phosphate (EMIM EP) and Butyl Methyl Phosphonium Methyl Sulfate (PSU). The first three are used to reveal the effects of both anion and cation chain length, while the other two are used to reveal the effect of anion and cation types. Tribological experiments are performed using a nanotribometer with a borosilicate ball rubbing against a silicon plate. 3D optical microscopy and X-ray Photoelectron Spectroscopy (XPS) are used to examine surface morphology and surface chemistry, respectively. The results showed that all parameters related to ILs’ chemistry have a strong influence on the tribological behaviour of the lubricated surfaces. The increase of anion/cation chain length leads to a significant decrease in wear and friction coefficients. The influence of anion and cation types appeared to vary depending on the contact pressure.

Implications of Imidazolium-Based Ionic Liquids as Refolding Additives for Urea-Induced Denatured Serum Albumins

One of the major challenges in protein stability is that proteins can easily unfold in the presence of denaturants like urea, which alters the native structure of proteins. There are numerous studies in which ionic liquids (ILs) act as promising biocompatible solvents (Bio-IL) for biomolecules. In this context, we present the refolding ability of biocompatible imidazolium-based ILs, 1-ethyl 3-methyl imidazolium ethyl sulfate [Emim][ESO₄] (IL-1) and 1-ethyl 3-methyl imidazolium chloride [Emim][Cl] (IL-2) against the chemically induced structural changes in bovine and human serum albumin (BSA and HSA). The work is substantiated with several spectroscopic, thermal and docking studies. In steady-state fluorescence spectroscopy, we observe that the emission intensity quenches for the protein in urea, which is reversible with the addition of ILs. Circular dichroism spectral studies reflect the reappearance of α helical content, which is a good indicator of the refolding ability of ILs. Further, thermal fluorescence studies showed that ILs have the ability to refold the urea-induced denatured protein at a higher temperature range only up to 7 M urea concentration; however, above 7 M urea concentration, IL somehow fails to refold the protein. The work is also supported by dynamic light scattering measurements, and the degree of BSA/HSA aggregation was reduced with the introduction of Bio-IL to the urea–BSA/urea–HSA system, ensuring the aggregate-free refolding. Furthermore, molecular docking studies were employed to probe the binding sites, and the results are well corroborated with the spectroscopic and thermal folding results. Therefore, through this paper, we aim to unravel the mechanistic intricacy of ILs using experimental and docking approaches. Overall, ILs act as recoiling medium for both native and unfolded (denatured by urea) BSA/HSA native structures.

Non-ionic surfactants and ionic liquids are a suitable combination for aqueous two-phase systems

The aqueous two-phase systems composed of the non-ionic surfactant Tergitol NP10 and the ionic liquids 1-ethyl-3-methyl imidazolium methylsulfate or 1-ethyl-3-methyl imidazolium ethylsulfate (C2C1imC1SO4 or C2C1imC2SO4) were characterized by the cloud point method. First, the binodal curves were determined and compared with the data reported previously for other non-ionic surfactants belonging to Tween and Triton families, observing that the systems belong to Treybal type 0 classification. Then, the experimental data were discussed in the light of the hydrophobicity of the surfactants and ionic liquids. The effect of the operation temperature (298.15, 313.15, 323.15, 333.15 K) was also evaluated at atmospheric pressure.

Studies of Volumetric and Viscosity Properties in Aqueous Solutions of Imidazolium Based Ionic Liquids at Different Temperatures and at Ambient Pressure

The ionic liquids (ILs) 1,3-dimethyl imidazolium methyl sulfate [MIm][MeSO4] and 1-ethyl-3-methyl imidazolium ethyl sulfate [EMIm][EtSO4] have been synthesized and characterized by 1H NMR, 13C NMR, mass spectrometry, TGA and DSC methods. The densities and viscosities of binary aqueous solutions of [MIm][MeSO4] (0.02458 to 0.18922 mol·kg−1) and [EMIm][EtSO4] (0.01044 to 0.21261 mol·kg−1) are reported at (293.15, 298.15 and 303.15) K and at ambient pressure. Apparent and partial molar volumes of the studied ILs are calculated at the studied concentrations. The limiting partial molar volumes of the studied ILs were obtained using an appropriate extrapolation method. The limiting apparent molar expansivity values at 298.15 K are also obtained. The relative viscosity data are analyzed by applying the Jones–Dole equation and Vand’s equations. Positive viscosity A and B coefficients were observed for both studied ILs, while the D coefficients were also found to be necessary, showing specific behavior depending upon the solute–solute interactions. Calculations of the B coefficients for anions are reported. The application of Vand’s equation to the viscosity data enabled us to calculate the Einstein–Simha factor (ν) and particle interaction coefficient ( $$Q$$ ) for the ion-pairs. The calculated ν values are found to be less than Einstein’s value of 2.5. The results are discussed from the points of view of the water structure making effect, solute–solvent hydrogen bond interaction and the presence of hydrophobic interaction.

Aqueous two-phase systems containing imidazolium ionic liquids and a Tween surfactant

Two imidazolium-based ionic liquids, 1-ethyl-3-methyl imidazolium methylsufate (C2C1imC1SO4) and 1-ethyl-3-methyl imidazolium ethylsulfate (C2C1imC2SO4), were tested as contenders for phase segregation in aqueous solutions of a non-ionic surfactant belonging to Tween family (Tween 20). Several empirical equations were used to correlate the binodal results which were previously obtained by means of the cloud point method at temperatures ranging from T=(298.15–333.15)K. The tie-lines have been determined by means of density and refractive indices measurement, and the Othmer-Tobias model was used to elucidate the thermodynamic consistence of these experimental values.

Micelle co-assembly in surfactant/ionic liquid mixtures

HypothesisThe phase behavior of amphiphiles is known to depend on their solvent environment. The organic character of ionic liquids suggested the possibility to tune surfactant aggregation, even in the absence of water, by selection of appropriate ionic liquid chemistry. To that end the behavior of the surfactant sodium dodecylsulfate in a chemically similar imidazolium ionic liquid, 1-ethyl-3-methyl imidazolium ethylsulfate, was explored. ExperimentsThe solubility of sodium dodecylsulfate in 1-ethyl-3-methyl imidazolium ethylsulfate was determined, establishing the Krafft temperature. Tensiometry was performed to obtain interfacial properties such as the surface excess and area per molecule. Pulsed-field gradient spin-echo NMR was used to determine the diffusion coefficients of all the major species, including micelles, as a function of surfactant concentration. Importantly, all three methods provided consistent values for the critical micelle concentration. FindingsAnalysis of tensiometry data suggests, and is confirmed by NMR results, that the ionic liquid ions are incorporated along with surfactants into micelles, revealing a complex micellization behavior. In light of these findings past studies with ternary mixtures of surfactants, ionic liquids, and water may merit additional scrutiny. Given the large number of ionic liquids, this work suggests opportunities to further control micelle formation and properties.

Microbial Adaptation to Ionic Liquids Increases the “Talent” to Treat Contaminants

Pseudomonas stutzeri strains are able to remediate different persistent contaminants, although they fail to treat efficiently industrial dyes. In this work, we have demonstrated that the acclimation of a Pseudomonas strain to the presence of the ionic liquid 1-ethyl-3-methyl imidazolium ethylsulfate can be a solution to remove two synthetic dyes widely found in wastewater effluents from textile industry: Acid Black 48 (AB48) and Reactive Black 5 (RB5), as model anthraquinone and diazo dyes, respectively. The remediation values achieved at small scale for both contaminants (individually and mixed) were higher than 75% in just 2 days. The process was scaled-up in a stirred tank bioreactor, and the levels of removal (greater than 80%) allowed confirming the suitability of the selected bioreactor configuration. All the obtained biomass and dye removal data were modeled by fitting to well-known equations in order to shed more light on the characteristics of the biotreatment process. The present work is the basis for the use of this microorganism at industrial scale, where different pollutants are found simultaneously in the same effluent.

Role of viscogens on the macromolecular assemblies of fibrinogen at liquid/air and solid/air interfaces.

In this study, an attempt has been made to understand the organization and association of fibrinogen (Fg) in solvent environment induced by viscogens such as 1-ethyl 3-methyl imidazolium ethyl sulfate (IL-emes), Ficoll, and Trehalose. The author observed that Fg in IL-emes adsorbed on solid surface shows higher β-sheet conformation. Shear viscosity measured using quartz crystal microbalance, for Fg in IL-emes was highest with a corresponding higher adsorbed mass 3.26 μg/cm(2). Associated assemblies of the protein at the liquid/air interface were monitored with changes in surface tension and were used to calculate work of adhesion. Changes in work of adhesion were used as a tool to measure the adsorption of Fg to solid surfaces in presence of viscogens and highest adsorption was observed for hydrophilic surfaces. Scanning electron microscopy images show Fg in trehalose forms elongated bead like structures implying organization of the protein at the interface. Crowding in the solvent environment induced by viscogens can slow down organization of Fg, leading to macromolecular assemblies near the interface.

Volumetric properties for binary and ternary mixtures of allyl alcohol, 1,3-dichloro-2-propanol and 1-ethyl-3-methyl imidazolium ethyl sulfate [Emim][EtSO4] from T = 298.15 to 318.15 K at ambient pressure

Based on density measurements, volumetric properties including excess molar volumes, partial molar volumes, partial molar excess volumes and their infinite dilution values, for binary and ternary solutions of allyl alcohol, 1,3-dichloro-2-propanol and 1-ethyl -3-methyl imidazolium ethyl sulfate [Emim][EtSO4] have been determined. Entire range of composition and temperatures from T=(298.15–318.15)K at ambient pressure (0.087MPa) have been considered. The excess molar volumes were negative for two binary mixtures including allyl alcohol whereas were positive for solutions of ionic liquid+1,3-dichloro-2-propanol. These quantities, for all binary mixtures, showed decrease by increasing temperatures which are explained based on intermolecular interactions and steric effects. Thermal expansion coefficients and their excess values have also been appraised for binary mixtures. The excess thermal expansion coefficients were negative for all binary mixtures and increased by raising temperature. The excess molar volumes have been modeled by Redlich–Kister equation for binary solutions and by Singh, Nagata–Tamura and Cibulka equations for ternary mixture.

Separation of aromatic solvents from oil refinery reformates by a newly designed ionic liquid using gas chromatography with flame ionization detection.

The aim of this study was to determine whether the new ionic liquid, N,N-dimethyl-2-oxopyrrolidonium iodide, synthesized in our laboratory is a suitable solvent for the separation of aromatic components benzene, toluene, ethylbenzene, and xylenes from petroleum mixtures (reformates) in liquid-liquid extraction. In pursuance of the above aim, a method to extract all components of a mixture, containing four aromatic components simultaneously, was developed. A new ionic liquid and a previously used liquid were compared for their extraction abilities. These ionic liquids were, respectively, N,N-dimethyl-2-oxopyrrolidinium iodide and 1-ethyl-3-methyl imidazolium ethyl sulfate. The concentrations of each benzene, toluene, ethylbenzene, and xylenes component in the extract and raffinate phases were measured by gas chromatography with flame ionization detection as volume percent to determine the extraction ability of the ionic liquids. The results obtained for both the reformate samples and model mixtures indicated that the new ionic liquid was effective as an extracting solvent for the recovery of aromatic components from reformates. Also the analysis results, using gas chromatography with flame ionization detection, for the reformate samples were as good as the results obtained by a local oil refinery. The extraction results also show that the developed method is very suitable for the separation and analysis of aromatic components in reformates.

Charging and softening, collapse, and crystallization of dipolar phospholipid membranes by aqueous ionic liquid solutions.

Ionic liquids have a variety of unique controllable structures and properties. These properties may be used to tailor the self-assembly of charged and dipolar biomolecules. Using solution X-ray scattering, we measured the structure of Dilauryl(C12:0)-sn-glycero-3-phospho-l-choline (DLPC), a dipolar (or zwitterionic) lipid, in the water-soluble room temperature ionic liquid Ethyl Methyl Imidazolium Ethyl Sulfate (EMIES) and mixtures of EMIES and water. We find that the interaction between the lipid bilayers is dominated by the balance between the charging of the polar headgroups by the ionic liquid, softening of the bilayer, and the osmotic pressure induced by the solvent. This balance leads to the following changes with increasing ionic liquid concentration: an incomplete unbinding transition from an attractive regime to a swollen regime of the lamellar phase formed by the bilayers. The swollen phase is followed by a collapse of the bilayers into a highly desolvated lamellar phase at some critical EMIES concentration, and eventually formation of lipid-crystalline phase, at very high EMIES concentrations. The latter phase is revealed by wide-angle X-ray scattering (WAXS) from the lipid solutions, showing multiple Bragg peaks, consistent with highly ordered structures. These structures were not observed in any other type of aqueous solutions containing monovalent or multivalent ions. The kinetics and temperature dependence of these transitions were also determined.

Ionic Liquids Confined in Hydrophilic Nanocontacts: Structure and Lubricity in the Presence of Water

We have investigated the influence of ambient humidity on the nanoconfined structure and response to shear of ionic liquids. Three ionic liquids (ILs) were selected, namely, 1-ethyl-3-methyl imidazolium ethylsulfate ([EMIM][EtSO4]), 1-ethyl-3-methyl imidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM][FAP]), and 1-hexyl-3-methyl imidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM][FAP]), to investigate the influence of hygroscopic and hydrophobic anions, as well as different alkyl chain lengths. We employed an extended surface forces apparatus (eSFA) to ascertain the structure of the confined films, whereas colloidal-probe lateral force microscopy (CPM) was used to measure shear forces in the nanosized contact between mica and a silica sphere. The presence of water, the anion, and the alkyl chain length of the imidazolium cation were found to influence the equilibrium structure of the nanoconfined film, as well as its dynamic properties. Adsorbed water appears to change both the ion-pair o...

Performance study of extraction and oxidation–extraction coupling processes in the removal of thiophenic compounds

Thiophenic sulfur removal was attempted in three different modes of operation, such as extraction, oxidation and simultaneous oxidation–extraction for a model fuel. Extraction was done using different solvents, viz., acetonitrile, dimethyl sulfoxide and 1-ethyl 3-methyl imidazolium ethyl sulfate at near ambient condition. The sulfur compounds tested were thiophene, benzothiophene and dibenzothiophene in iso-octane. Titanium silicate-1 and titanium-beta catalysts were used for oxidation of the compounds. A detailed parametric study was performed varying stirring time, extraction temperature and amount of solvent, to investigate their effects on the extraction of the three sulfur compounds. Simultaneous oxidation–extraction process showed a significant amount of sulfur removal. Dimethyl sulfoxide was found to be the best solvent for extraction.

Ionic Liquid Doped β Lactoglobulin as Template for Nanoclusters of Nickel Oxide

In this work, Langmuir films of organized assemblies of β-lactoglobulin (βLG) with 1-ethyl-3-methyl imidazolium ethyl sulfate (IL-emes) have been characterized at air/water interface using surface pressure-specific area isotherms and dilational rheology. The protein in the IL-mediated assembly shows excellent packing at the interface and is stable as seen in circular dichroic spectroscopy. These spread films on nickel chloride were transferred as Langmuir–Schaffer films of βLG and βLG+IL-emes and used as template for designing nanoclusters of nickel oxide. The nanoclusters have been characterized using transmission electron microscopy (TEM) and powder XRD. While pure protein template gives needle-shaped structures, the IL-mediated template gives spherical shapes of hexagonal nickel oxide in the range 30 nm to 40 nm. Presence of ionic liquid seems to slow down the growth of the cluster and also prevents aggregation of the clusters.

Ionic liquids improve the anticorrosion performance of Zn-rich coatings

In this work, the suitability of the ionic liquid 1-ethyl-3-methyl imidazolium ethylsulfate (C2C1imC2SO4) for improving the anticorrosive behaviour of zinc rich paints (ZRP) has been demonstrated.

Effects of ionic liquid mixtures on lipid extraction from Chlorella vulgaris

In this study, pre-biodiesel-production lipid extraction from microalgae (Chlorella vulgaris) was performed. The yield-enhancing effects of ionic liquid blends on the lipid extraction were investigated. The initial fatty acids content of the C. vulgaris was 292.2 mg/g cell. The lipid extraction yield using single ionic liquids was compared with the yield obtained with organic solvents and ionic liquid mixtures, respectively. The yield by hexane–methanol solvent was 185.4 mg/g cell. Among the 12 ionic liquids, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-methyl imidazolium diethylphosphate, 1-ethyl-3-methyl imidazolium tetrafluoroborate, and 1-ethyl-3-methyl imidazolium chloride showed high (>200.0 mg/g cell) lipid extraction yields. Although the yields of 1-ethyl-3-methyl imidazolium ethyl sulfate and 1-ethyl-3-methyl imidazolium thiocyanate were only 60.5 and 42.7 mg/g cell, respectively, the yield for their mixture (weight ratio of 1:1) was improved to 158.2 mg/g cell. Similarly, whereas the lipid extraction yield of 1-ethyl-3-methyl imidazolium hydrogen sulfate was just 35.2 mg/g cell, that for its mixture with 1-ethyl-3-methyl imidazolium thiocyanate (weight ratio of 1:1) was boosted to 200.6 mg/g cell. Overall, the synergistic effects of the ionic liquid mixtures with different anions improved the lipid extraction yield of C. vulgaris.

Solubility of gases in 1-alkyl-3methylimidazolium alkyl sulfate ionic liquids: Experimental determination and modeling

The solubility of different gases (carbon dioxide, methane, ethane, carbon monoxide and hydrogen) in ionic liquids with an alkyl sulfate anion has been modeled with the Group Contribution equation of state developed by Skjold-Jørgensen. New gas solubility measurements have been carried out with a high pressure magnetic suspension balance in order to cover pressure and temperature ranges not considered in previous studies and to obtain more experimental information for the correlation of parameters of the equation of state. New solubility measurements include the solubility of carbon dioxide in 1-ethyl 3-methyl imidazolium ethyl sulfate [emim][EtSO4] at temperatures of 298K and 348K and pressures ranging from 0.3MPa to 6.5MPa, the solubility of methane in [emim][EtSO4] at a temperature of 293K and pressures ranging from 0.2MPa to 10.2MPa, and the solubility of ethane in [emim][EtSO4] at temperatures of 323K and 350K and pressures ranging from 0.2MPa to 4MPa. Results show that the Group Contribution equation of state can be used to describe the solubility of gases in alkyl sulfate ionic liquids as well as infinite dilution coefficients of alkanes in the ionic liquids, with average deviations between experiments and calculations ranging from 1% to 10% in the case of mixtures with CO2, CO, CH4 and H2 with the alkyl sulfate ionic liquids to up to 34% in the case of the solubility of ethane in [emim][EtSO4].

Probing the electrochemical double layer of an ionic liquid using voltammetry and impedance spectroscopy: A comparative study of carbon nanotube and glassy carbon electrodes in [EMIM]+[EtSO4

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are compared as techniques for analyzing double layer capacitances of ionic liquids (ILs) at the surfaces of two carbon-based electrodes. These systems are relevant for energy storage supercapacitors and often are associated with unconventional electrochemical properties. Certain theoretical and experimental aspects of CV and EIS necessary for quantitative evaluation of the capacitance characteristics of such systems are explored. The experiments use 1-ethyl-3-methyl imidazolium ethylsulfate as a model IL electrolyte in combination with a porous electrode of carbon nanotubes (CNTs). The results are compared with those obtained with a nonporous glassy carbon (GC) electrode. The time is constant, and hence the power delivery characteristics of the experimental cell are affected by the electrolyte resistance and residual faradaic reactions of the IL, as well as by the spatially inhomogeneous electrode surfaces. It is shown that adequate characterization of these IL-electrode systems can be achieved by combining CV with EIS. A phenomenological framework for utilizing this combination is discussed.

D.C. voltammetry of ionic liquid-based capacitors: Effects of Faradaic reactions, electrolyte resistance and voltage scan speed investigated using an electrode of carbon nanotubes in EMIM-EtSO 4

Carbon nanotube (CNT) electrodes in combination with ionic liquid (IL) electrolytes are potentially important for energy storage systems. We report electrochemical investigation of such a system involving a paper-electrode of multi-wall CNT (MWCNT) in the IL of 1-ethyl-3-methyl imidazolium ethylsulfate (EMIM-EtSO 4). Our study concentrates on the analytical aspects of cyclic voltammetry (CV) to probe the double layer capacitance of these relatively unconventional systems (that involve rather large charge–discharge time constants). Both theoretical and experimental aspects of CV for such systems are discussed, focusing in particular, on the effects of Faradaic side-reactions, electrolyte resistance and voltage scan speeds. The results are analyzed using an electrode equivalent circuit (EEC) model, demonstrating a method to account for the typical artifacts expected in CV of CNT–IL interfaces.