Ionic Liquid Mixtures Research Articles

Effect of cation size of binary cation ionic liquid mixtures on capacitive energy storage

Ionic liquid mixtures show promise as electrolytes for supercapacitors with nanoporous electrodes. Herein, we investigate theoretically and with experiments how binary electrolytes comprising a common anion and two types of differently-sized cations affect capacitive energy storage. We find that such electrolytes can enhance the capacitance of single nanopores and nanoporous electrodes under potential differences negative relative to the potential of zero charge. For a two-electrode cell, however, they are beneficial only at low and intermediate cell voltages, while a neat ionic liquid performs better at higher voltages. We reveal subtle effects of how the distribution of pores accessible to different types of ions correlates with charge storage and suggest approaches to increase capacitance and stored energy density with ionic liquid mixtures.

A combined experimental and theoretical study on the structures, dynamics and interactions of BMIMTfO and BMIMTFSI binary ionic liquid mixtures

The study of ionic liquid mixtures has garnered growing attention due to its importance. However, our current understanding of molecular interactions in ionic liquid mixtures remains incomplete, necessitating further research to expand the foundational knowledge in this field. In this work, a comprehensive approach incorporating theoretical calculations and diverse experimental techniques was utilized to research the structures, dynamics, and interactions of 1-butyl-3-methylimidazolium trifluoromethansulfonate (BMIMTfO) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (BMIMTFSI) mixtures. The obtained conclusions are as follows: (1) The primary interaction sites for [BMIM]+, [TfO]− and [TFSI]− were identified as the C2H, O atoms of SO3 and O atoms of SO, respectively. (2) With the addition of BMIMTFSI, the hydrogen bonding interactions associated with imidazolium CH are weakened, while those associated with alkyl CH and SO are strengthened. Additionally, there is an increased propensity for aggregation between the two anions ([TfO]−, [TFSI]−) and [BMIM]+. (3) The interactions between [BMIM]+ and [TfO]− are stronger compared to those between [BMIM]+ and [TFSI]−, and the self-diffusion coefficient followed the order of [BMIM]+ > [TFSI]− > [TfO]−. (4) The 2[BMIM]+[TfO]−, 2[BMIM]+[TFSI]−-[TfO]−, 2[BMIM]+[TFSI]− and 2[BMIM]+[TfO]−-[TFSI]− complexes were assigned using excess spectroscopy and quantum chemical calculations.

Synergism in mixtures of nano benzimidazolium Gemini ionic liquid and sodium dodecyl sulfate surfactants in tuning interfacial properties of crude oil−water system

The high price of newly explored surfactants is a concern in applications, but their mixture with conventional surfactants can bring about desired outcomes. Gemini surface active ionic liquids (GSAILs) have emerged as unique materials in tuning interface properties. Surfactants like sodium dodecyl sulfate (SDS), on the other hand, are known effective and commercially available. This study investigates the simultaneous effects of a benzimidazolium cationic GSAIL, [C4benzim-C6-benzimC4][Br2], and SDS surfactants on the interfacial tension (IFT), emulsification, and wettability alteration of the crude oil−water system. The results demonstrate amazing synergies up to 97.6 % in the IFT reduction. An ultra-low IFT of 0.16 mN·m−1 was achieved with an optimum GSAIL mole fraction of 0.4, attributed to the attractive interaction between the cationic GSAIL and the anionic SDS. Mixtures also give 54.3 and 72.8 % synergies in emulsification and wettability alteration, respectively. The adsorption of individual and mixture of surfactants were theoretically analyzed using the Frumkin adsorption isotherm and the non-ideal interactions of the binary mixtures (NIBM) theory. The corresponding determined parameters were consistent. To have a more comprehensive analysis, the results were compared with those obtained with an analogous structure imidazolium GSAIL.

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.

Theoretical and Experimental Study of CO2 Absorption by N-2-ethylhexylethylenediaminium-TFS Type Protic Ionic Liquid

The CO2 absorption using the mixture of ethylenediaminium type protic ionic liquid [HEtHexen][TFS] and H2O with different molar ratio was investigated by the measurement of pH, density, viscosity and conductivity at 30°C. Meanwhile, we studied the hydrogen bonding between [HEtHexen][TFS] and CO2 using DFT calculation, the result of the interaction energy, vibration frequency and second-order perturbation energy, etc. shows that a weak or medium strength N-H···O type hydrogen bonding occurred between [HEtHexen][TFS] and nCO2 (n=1−4). The result of experimental and theoretical study indicates that one [HEtHexen][TFS] molecule absorbed a maximum of three molecules of CO2.

Theory-Enabled High-Throughput Screening of Ion Dissociation Explains Conductivity Enhancements in Diluted Ionic Liquid Mixtures

Theory-Enabled High-Throughput Screening of Ion Dissociation Explains Conductivity Enhancements in Diluted Ionic Liquid Mixtures

The azeotropy eliminating mechanism of ethyl acetate-acetonitrile system via ionic liquid entrainer: A combination of FTIR and DFT study

Ionic liquids (ILs) are good candidates for azeotropy separation. Knowledge of the microstructure properties of azeotrope − IL mixtures is important because they could reveal the molecular intrinsic cause of the elimination of azeotropy and represent the basis for the practical process. In this work, the microstructures of ethyl acetate-acetonitrile azeotrope mixtures and a representative IL, 1‑butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N], which could eliminate the azeotropy of the ethyl acetate-acetonitrile system, were studied by Fourier transform infrared spectroscopy with the assistance of quantum chemical calculations and excess spectra. The C≡N stretching vibrational region of acetonitrile was closely examined. The interaction complexes of ethyl acetate-acetonitrile and ion cluster/ion pair/ion − acetonitrile were identified. Weak strength hydrogen-bonds with electrostatically dominant and closed-shell interaction properties were found in these complexes. The interactions between [BMIM][Tf2N] and acetonitrile were stronger than those between ethyl acetate and acetonitrile, which caused the addition of IL to easily destroy the ethyl acetate-acetonitrile interaction complex. The interactions between [BMIM][Tf2N] and acetonitrile were stronger than those between [BMIM][Tf2N] and ethyl acetate, which would influence the relative volatility of ethyl acetate and acetonitrile in the azeotrope system. When x(IL) was larger than 0.027, all the interaction complexes between acetonitrile and ethyl acetate were completely broken apart, and the azeotrope was eliminated.

Structure and Conformational Properties of a Short Polyaniline Chain in a Mixture of Water and Ionic Liquid [1-Ethyl-3-methyl-imidazolium][bistriflimide] Investigated by All-Atom Molecular Dynamics Simulations.

Development of antifouling membranes for water treatment using conducting polymers and their composites is a fundamental strategy to mitigate the fouling. This manuscript presents an all-atom molecular dynamics simulations of a conducting polymer, polyaniline (PANI), immersed in an ionic liquids (ILs)-water mixtures. We have considered the ionic liquid 1-ethyl-3-methyl imidazolium bistriflimide, [EMIM]+[BIS]-. The two forms of polyaniline, emeraldine base (EB) and emeraldine salt (ES), were considered. Various intra- and intermolecular structural properties of PANI were analyzed, such as polymer chain radius of gyration Rg, radial distribution functions, and torsional angle distributions. The Rg of EB shows an increase, while the Rg of ES shows a decrease with an increase in the IL concentration. The backbone torsional angle probability distributions show a significant trans state for EB, while a combination of trans and gauche states was observed for ES. Similar supportive distributions were seen in the backbone angular distributions. Radial distribution functions between the carbon atoms at ortho and meta positions of the benzene ring on both ES and EB, as well as the amine group attached between two benzene rings, show an enhanced interaction with the ionic liquid compared to water. Anions have a dominant interaction with the polymer chain when compared to cations. The solvent accessible surface area (SASA) calculations were in accordance with the EB and ES structural properties. The SASA values are more favorable for ES than for EB. H-bond analysis shows a decrease in the number of H-bonds with water as the IL concentration increases.

Investigation of Programmable Friction with Ionic Liquid Mixtures at the Nano- and Macroscales

Non-mechanical stimuli are used to directly control or program the friction properties of tribosystems. For this purpose, an ionic liquid is used as a lubricant that affects and controls the friction in the presence of external triggers. Here, it is shown that the friction behavior of two surfaces in sliding contact can be controlled and permanently changed by applying an electrical potential to an ionic liquid mixture (ILM). This change in the friction properties was demonstrated both at the nanoscale using an atomic force microscopy (AFM)-based friction force microscopy (FFM) and at the macroscale using a specially designed tribo-setup cell. In tribology, the linking of these two scales of magnitude represents one of the greatest obstacles between basic research and the step towards application-oriented system development and is therefore of fundamental importance. In addition, other parameters affecting the tribological behavior of the system, such as roughness, lubricant film thickness, and wear behavior, were investigated as a function of the electrical potentials. The correlation between the structure of surface-bound ionic liquid layers and the friction behavior can be used to control friction, thus enabling a first step towards tribosystems that automatically adapt to changing conditions.

Evaluation of tribological behavior of a circulation oil with ionic liquid and hybrid additives

In this study, the synergistic effects of methyltrioctylammonium bis(trifluoromethylsulfonyl)imide [N1888] [NTf2] ionic liquid (IL) with zinc dialkyldithiophosphate (ZDDP) and zinc oxide (ZnO) nanoparticles (NPs) as hybrid additives in a circulation oil for steel–steel contacts at different temperatures. The wear test results indicated that the additions of single additives (IL, ZDDP, and ZnO NPs) could enhance the tribological performance of the circulation oil. Among these additives, the IL exhibited the most effective at the same weight concentration blended into the tested oil. The mixture of IL and ZDDP showed superior friction-reducing and wear-reducing properties compared to the IL + ZnO formulation. The hybrid additive formulation consisting of 0.5 wt% IL, 0.25 wt% ZDDP, and 0.25 wt% ZnO NPs exhibited excellent tribological properties at higher temperatures in the boundary lubrication regime. Analysis using scanning electron microscopy/energy dispersive X-ray reveals that all single additives contribute to the formation of a tribofilm wear mechanism. However, the role of ZnO NPs in the hybrid additive conditions was changed from the most likely tribosintering effect to the most likely nano bearing effect at 100 °C. The interactions among IL, ZDDP, and NPs examined in this study can provide fundamental insights for the development of future lubricants.

Insights into the estimation of surface tensions of mixtures based on designable green materials using an ensemble learning scheme

Precise estimation of the physical properties of both ionic liquids (ILs) and their mixtures is crucial for engineers to successfully design new industrial processes. Among these properties, surface tension is especially important. It’s not only necessary to have knowledge of the properties of pure ILs, but also of their mixtures to ensure optimal utilization in a variety of applications. In this regard, this study aimed to evaluate the effectiveness of Stochastic Gradient Boosting (SGB) tree in modeling surface tensions of binary mixtures of various ionic liquids (ILs) using a comprehensive dataset. The dataset comprised 4010 experimental data points from 48 different ILs and 20 non-IL components, covering a surface tension range of 0.0157–0.0727 N m−1 across a temperature range of 278.15–348.15 K. The study found that the estimated values were in good agreement with the reported experimental data, as evidenced by a high correlation coefficient (R) and a low Mean Relative Absolute Error of greater than 0.999 and less than 0.004, respectively. In addition, the results of the used SGB model were compared to the results of SVM, GA-SVM, GA-LSSVM, CSA-LSSVM, GMDH-PNN, three based ANNs, PSO-ANN, GA-ANN, ICA-ANN, TLBO-ANN, ANFIS, ANFIS-ACO, ANFIS-DE, ANFIS-GA, ANFIS-PSO, and MGGP models. In terms of the accuracy, the SGB model is better and provides significantly lower deviations compared to the other techniques. Also, an evaluation was conducted to determine the importance of each variable in predicting surface tension, which revealed that the most influential factor was the mole fraction of IL. In the end, William’s plot was utilized to investigate the model's applicability range. As the majority of data points, i.e. 98.5% of the whole dataset, were well within the safety margin, it was concluded that the proposed model had a high applicability domain and its predictions were valid and reliable.

Phase Separation and Ion Diffusion in Ionic Liquid, Organic Solvent, and Lithium Salt Electrolyte Mixtures.

The highly desirable characteristics of ternary mixtures of ionic liquids, organic solvents, and metal salts make them a promising candidate for use in various electrothermal energy storage and conversion systems. In this study, using large-scale classical molecular dynamics simulations, we looked into 10 different ternary electrolyte mixtures using combinations of [EMIM]+, [BMIM]+, and [OMIM]+ cations with [NO3]-, [BF4]-, [PF6]-, [ClO4]-, [TFO]-, and [NTf2]- anions, tetraglyme, and Li salt to study the effect of ionic liquid composition on the phase behavior of ternary electrolyte mixtures. We uncovered that in these electrolytes, phase separation is mainly a function of pairwise binding energy of the constituents of the mixture. To corroborate this theory, several simulations are performed at various temperatures ranging from 260 to 500 K for each mixture, followed by calculating the binding energy of ionic liquid pairs using density functional theory. Our results verify that the transition temperature for the phase separation of each system is indeed a function of the pairwise binding energy of its ionic liquid pairs. It is also found that in some cases, the diffusion coefficient of the Li+ ions decreased even with the increase in the temperature, an effect that is attributed to the presence of condensed ionic domains in the electrolyte. This study provides a new insight for the design of multicomponent electrolyte mixtures for a wide range of energy applications.

Understanding the Liquid Structure in Mixtures of Ionic Liquids with Semiperfluoroalkyl or Alkyl Chains.

By mixing ionic liquids (ILs), it is possible to fine-tune their bulk and interfacial structure. This alters their physical properties and solvation behavior and is a simple way to prepare a collection of ILs whose properties can be tuned to optimize a specific application. In this study, mixtures of perfluorinated and alkylated ILs have been prepared, and links between composition, properties, and nanostructure have been investigated. These different classes of ILs vary substantially in the flexibility and polarizability of their chains. Thus, a range of useful structural and physical property variations are accessible through mixing that will expand the library of IL mixtures available in an area that to this point has received relatively little attention. In the experiments presented herein, the physical properties and bulk structure of mixtures of 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM][Tf2N] and 1-(1H,1H,2H,2H-perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM-F13][Tf2N] have been prepared. The bulk liquid structure was investigated using a combination of small-angle X-ray and neutron scattering (SAXS and SANS, respectively) experiments in combination with atomistic molecular dynamics simulations and the measurement of density and viscosity. We observed that the addition of [C8MIM-F13][Tf2N] to [C8MIM][Tf2N] causes changes in the nanostructure of the IL mixtures that are dependent on composition so that variation in the characteristic short-range correlations is observed as a function of composition. Thus, while the length scales associated with the apolar regions (polar non-polar peak─PNPP) increase with the proportion of [C8MIM-F13][Tf2N] in the mixtures, perhaps surprisingly given the greater volume of the fluorocarbon chains, the length scale of the charge-ordering peak decreases. Interestingly, consideration of the contact peak shows that its origins are both in the direct anion···cation contact length scale and the nature (and hence volume) of the chains appended to the imidazolium cation.

Novel electrolytes based on mixtures of dimethyl sulfoxide task specific zwitterionic ionic liquid and lithium salts: Synthesis and conductivity studies

Novel methyl sulfoxide imidazolium-based zwitterionic low melting salts was synthesized and characterized. The combination of this functionalized zwitterion and lithium bis(trifluoromethylsulfonyl)amide (LiNTf2) salts at different molar ratios of render to low melting mixtures, which can exhibit an ionic conductivity as high as 3.4 × 10−5 S cm−1 at 30 °C or 2.9 × 10−3 S cm−1 at 120 °C and a high thermal decomposition temperature higher than 250 °C. The thermal activation energy shown two clearly different Arrhenius trend. For all the mixtures the temperature where the slope of the Arrhenius plot changes is on the range of the melting temperature experimentally observed for the mixture. Below the melting temperature, the values of activation energy are around of two times higher than the values observed for all the mixtures above the melting temperature. On the other hand, in all the mixtures, we have observed that conductivity increases monotonically on the composition of the mixture. These non-volatile and highly polar novel materials can be used for the development of devices targeting high ionic Li-ion conductivity.

Behavior of astatine and bismuth in non-conventional solvents: Extraction into imidazolium-based ionic liquid and methyl anthranilate with active pharmaceuticals binary mixtures from nitric acid media

Astatine is one of the least chemically studied elements and its behavior in the presence of non-conventional solvents has not been investigated before. This work considers both hydrophobic ionic liquids and binary mixtures as alternatives to conventional solvents. The study is based on the extraction of astatine and bismuth (target material required to produce astatine) into imidazolium-based ionic liquid, and binary mixtures formed by active pharmaceuticals (ibuprofen, lidocaine) and a food-grade ingredient (methyl anthranilate). It is shown that both the ionic liquid and binary mixtures can successfully extract At from nitric acid media, but extraction of Bi into the ionic liquid is very inefficient, resulting in a good separation factor for these two elements in the entire studied acidity range. Extraction of At into binary mixtures is very efficient, having distribution ratio values as high as 1000, while the behavior of Bi under these conditions depends on the composition of the mixture. A mathematical model has been developed to fit both At and Bi experimental data and applied to determine corresponding thermodynamic extraction constants.

Solubility and Solvation Properties of Pharmaceutically Active Ionic Liquid Benzocainium Ibuprofenate in Natural Deep Eutectic Solvent Menthol-Lauric Acid.

Due to their appealing physiochemical properties, particularly in the pharmaceutical industry, deep eutectic solvents (DESs) and ionic liquids (ILs) are utilized in various research fields and industries. The presented research analyzes the thermodynamic properties of a deep eutectic solvent created from natural molecules, menthol and lauric acid in a 2:1 molar ratio, and an ionic liquid based on two active pharmaceutical ingredients, benzocainium ibuprofenate. Initially, the low solubility of benzocainium ibuprofenate in water was observed, and a hydrophobic natural deep eutectic mixture of menthol:lauric acid in a 2:1 ratio was prepared to improve benzocainium ibuprofenate solubility. In order to determine the solvent properties of DESs and ILs mixtures at different temperatures and their molecular interactions to enhance the solvent performance, the apparent molar volume, limiting apparent molar expansibility, and viscosity B coefficient were estimated in temperature range from 293.15 K to 313.15 K and varying concentration of benzocainium ibuprofenate.

In-situ crosslinking of polysiloxane electrolyte within Al2O3@SiNWs for quasi-solid-state micro-supercapacitors

Developing flexible solid-state micro-supercapacitors with large potential window is crucial for many technologies. The present study focuses on the synthesis and elaboration of quasi-solid-state (QSS) electrolytes with an electrochemical stability greater than 3.0 V based on functionalized polysiloxane. Their electrochemical behavior was studied with silicon nanowires electrodes. The polysiloxane was functionalized with both ammonium and cross-linkable functions. The nanostructured electrodes were impregnated with a mixture of ionic liquid and functionalized polysiloxane. The crosslinking of the polymer electrolyte was then performed by thermal curing directly within the nanostructured electrodes. The quasi-solid system exhibits very high stability upon galvanostatic cycling i.e. during 100 000 cycles with a cell potential of 3.0 V only a capacitance loss of 2.10−5% per cycle was registered. The performance of this QSS with safe electrolyte is remarkable.

Cellulose dissolution in mixtures of ionic liquids and molecular solvents: The fruitful synergism of experiment and theory

We investigated the dependence of dissolution of microcrystalline cellulose (MCC) in binary solvent mixtures of ionic liquids (ILs) and the molecular solvents (MSs) N,N-dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO). The ILs we used are based on 1-(n-butyl)-3-methylimidazolium cation, BuMeIm+, with acetate (AcO−) and chloride (Cl−) anions. As experimental variables, we changed the mole fraction of the MS (χDMAc or χDMSO) and the temperature (T). MCC dissolution was determined using an optical microscope and expressed on the mass fraction scale (m%). The order of maximum m% was BuMeImAcO-DMSO > BuMeImAcO-DMAc ≫ BuMeImCl-DMSO. To rationalize this dependence, we used molecular dynamics (MD) simulations employing, as a model for cellulose, a crystallite of eight chains, each containing ten anhydroglucose units (AGUs). We calculated the root-mean-square-deviation (RMSD) and the radial distribution function, g(r). Values of RMSD showed that the separation of decamer-chains follows the same order as the maximum m%; more chain separation was taken to indicate greater crystallite dissolution. Additionally, the maximum values and the sharpness of the g(r) peaks followed the same order of dissolution, due to a combination of hydrogen bonding between the hydroxyl groups of the AGU and ions of the IL. We also recorded the turbidity of MCC-IL-DMSO solutions and the conductance of cellobiose-IL-MS solutions; the results of both experiments corroborated our interpretations of the MD simulation results. Our study suggests that MD simulations can be fruitfully employed to predict the best candidates among a series of solvents, e.g., IL-MS. This screening saves labor and material in the search for optimal solvents for cellulose dissolution.

Mixtures of ethylammonium nitrate and ethylene carbonate: Bulk and interfacial analysis

The structure and dynamics of binary mixtures of a protic ionic liquid (ethylammonium nitrate) and ethylene carbonate are studied by means of atomistic molecular dynamics simulations and experimental measurements both in bulk and at the electrochemical interface. The solubility limit was experimentally found at 0.6 carbonate molar fraction. Likewise, density and conductivity experimental data are compared with computational results. Also, distribution and correlation functions obtained from bulk simulations are analyzed in the miscible range to clarify the role of the carbonate in the coordination and diffusion of ionic species. Understanding the evolution of the hydrogen bond network is of particular importance since its strength is detected as the most relevant feature in the structural organization of the mixture. Regarding the effects of the presence of an interface, the orientations of the molecules and the density and charge profiles are calculated both in the absence and in the presence of an electric field. This analysis reveals the tendency of the carbonate to displace the ionic liquid from the near-wall region when concentration is increased.

Surface tension and viscosity of binary ionic liquid mixtures from high vacuum up to pressures of 10 MPa

In the present study, we investigated the surface tension and viscosity of binary ionic liquid (IL) mixtures at or close to saturation conditions from high vacuum conditions up to elevated pressures. We studied four different mixtures of 1,3-bis(2-(2-methoxyethoxy)ethyl)imida-zolium iodide ([(mPEG2)2Im]I) and 1-methyl-3-octylimidazolium hexafluorophosphate ([C8C1Im][PF6]) with [C8C1Im][PF6] mole contents between (4.6 and 49.8) mol%. Argon (Ar) gas of relatively low solubility was used to vary the applied pressure between (0.1 and 10) MPa. For temperatures from (303 to 363) K, the surface tension obtained by the pendant-drop (PD) method was used to determine the saturated liquid viscosity from surface light scattering (SLS). These studies are complemented by additional PD measurements under ultraclean high vacuum (HV) conditions in a second setup. At about 0.1 MPa, the surface tension and viscosity of the IL mixtures show negative deviations from a linear mixing rule based on the molar bulk composition, which is more pronounced at lower temperatures. The surface tension values at 0.1 MPa and under HV agree with each other and lie closer to the values of [C8C1Im][PF6] that has a distinctly lower surface tension than [(mPEG2)2Im]I and is surface-active. For the equimolar IL mixture at 303 K, an increase in the pressure up to 10 MPa has a negligible influence on the viscosity, while it causes a distinct reduction in the surface tension compared to the value at 0.1 MPa. The pressure-dependent relative change for the viscosity of the ternary mixtures of the two ILs and Ar corresponds well to the mean values of the positive and negative relative changes observed for the two binary [(mPEG2)2Im]I-Ar and [C8C1Im][PF6]-Ar subsystems, respectively. For the surface tension, the absolute changes at a given pressure are very similar regardless of the IL bulk composition, suggesting a similar weak Ar enrichment at the gas–liquid interface.