Binary Mixtures Of Ionic Liquids Research Articles

Applications of a preferential–solvation index (PSI) for the comparison of binary mixtures with ionic liquids

Applications of a preferential–solvation index (PSI) for comparing analogous binary mixtures with ionic liquids (ILs) are described with the analysis of more than sixty examples from the literature. Interesting trends and patterns are revealed, confirming conclusions based on more elaborate treatments, or disclosing puzzling discontinuities by comparison of analogous mixtures. The obtained trends also question the meaning of fitting parameters from classic models of preferential solvation and the existence of postulated entities that are hard to be conceived in binary mixtures of ILs.

Density, Speeds of Sound, and Refractive Index of Pure and Binary Mixtures of Ionic Liquids Based on Imidazolium Cations and Tetrafluoroborate Anions with Cyclohexylamine

Density, Speeds of Sound, and Refractive Index of Pure and Binary Mixtures of Ionic Liquids Based on Imidazolium Cations and Tetrafluoroborate Anions with Cyclohexylamine

Developing machine learning models for ionic conductivity of imidazolium-based ionic liquids

In this study, we developed two machine learning models: - support vector machine (SVM) and artificial neural network (ANN) - to correlate ionic conductivity of pure ionic liquids based on the imidazolium cations using the data acquired from the NIST ILThermo database. Both models were shown to successfully capture the entire range of ionic conductivity spanning six orders of magnitude over a temperature range of 275–475 K with relatively low statistical uncertainty. Due to slightly better performance, ANN was used to predict the ionic conductivity for 1102 ionic liquids formed from every possible combination of 29 cations and 38 anions contained in the database. The procedure led to the generation of many ionic liquids for which the ionic conductivity was estimated to be greater than 1 S/m. The ionic liquid dimethylimidazolium dicyanamide, not present in the original dataset, was identified to exhibit the ionic conductivity of 3.70 S/m, roughly 30% higher than the highest conductivity reported for any ionic liquid at 298 K in the database. The ANN model was also found to accurately predict the ionic conductivity for several ionic liquid-ionic liquid mixtures, for which experimental data are available. Encouraged by this result, we calculated ionic conductivity for all the possible binary ionic liquid-ionic liquid mixtures based on the cations and anions in the dataset. The model predictions revealed a large number of ionic liquid mixtures systems exhibiting nonideal behavior where a maximum or minimum in the ionic conductivity was observed as a function of composition, similar to trends seen in binary ionic liquid mixture of water or conventional solvents with ionic liquids.

Binary mixtures of ionic liquids: Ideal, non-ideal, or quasi-ideal?

The mixing of ILs provides an opportunity for fine tuning the physiochemical properties of ILs for various applications. However, a suitable mixture having desired properties can only be designed when the physiochemical properties of the mixtures of ILs along with their spectroscopic properties are well understood. With an aim to achieve this objective, three different mixtures with a common anion, namely, [C2C1im][C4C1im][NTf2], [C3C1pyr][C4C1pyr][NTf2], and [C3C1im][C3C1pyr][NTf2], have been investigated in the current study. Investigations have been carried out at the macroscopic level by observing the thermophysical properties, such as molar volume and thermal expansion coefficient, and at the microscopic level with time-resolved fluorescence measurements and the pulse field gradient nuclear magnetic resonance (NMR) technique. The results obtained from the thermophysical study have indicated that excess molar volume for imidazolium-based IL-IL mixtures may be linked to the free volume created by the alkyl chain of the imidazolium cation whereas for the mixture of pyrrolidinium ILs, lowering of density can give rise to free volume. Analysis of time-resolved fluorescence anisotropy data has provided clear evidence in favor of the presence of free volume in the binary mixture of ILs. NMR studies have also supported the fluorescence anisotropy data. The outcome of the present investigation reveals that the mixtures show appreciable deviation from ideal behavior and the deviation from the ideal behavior is caused due to the generation of free volume in the resultant mixture, describing these IL mixtures as quasi-ideal rather than ideal or non-ideal.

Binary mixtures of homologous room-temperature ionic liquids: Temperature and composition evolution of the nanoscale structure

Using X-ray scattering from binary mixtures of [Cnmim][NTf2] room temperature ionic liquids (RTILs) with n=8,12 we study their nanoscale layering and its evolution with temperature T and mole fraction x of [C8mim][NTf2]. The layers’ lateral structure, dominated by the common headgroups’ Coulomb interaction in the layer’s polar slab, and by the chain-chain van der Waals interaction in the apolar slab, hardly changes. However, the longitudinal layer spacing, dI, decreases with x, exhibiting domination by [C12mim][NTf2] at least up to x≈0.5. The layering order’s range decreases uniformly with x. dI is found to deviate positively from an ideal mixture spacing by up to ≲5%. The lateral spacings’ deviations are 10-fold smaller, implying the nanoscale excess volume to be also ≲5%, 100-fold larger than those obtained from macroscopic molar density measurements. This gap is probably bridged at the larger length scales of these RTILs’ hierarchical order. Increasing T decreases the dI deviations, but only marginally. The positive, and T-decreasing, dI deviations from ideality contrast strongly with the negative, 100-fold smaller, and T-increasing, deviations found for liquid normal-alkane mixtures of the same lengths, but fully agree with the positive similar-percent deviations obtained from the modified Vegard’s law for soft-solid rotator phases of binary mixtures of alkanes and of alcohols. These results attest against a liquid-like chain packing in the apolar slab of the RTILs, but strongly support an interdigitated, roughly layer normal, chain packing.

Hydrogen Bond Kinetics, Ionic Dynamics, and Voids in the Binary Mixtures of Protic Ionic Liquids with Alkanolamines.

Classical molecular dynamics simulations were used to investigate the structural and dynamical properties of the mixtures of ionic liquids (ILs) with the conjugate forms of the cation in a 1:1 molar ratio. The experimental studies suggested the combination of ethanolamines and ILs as novel absorbents for acidic gases such as CO2 and H2S, which provide the advantage of efficient absorption of gases at low pressures. However, the microscopic properties of the ionic mixtures are not studied. From our computational investigations, the densities of mixtures are reported and compared with the experimental results. The structural evolution of mixtures is reported by radial distribution functions, coordination numbers, void analysis, and spatial distribution functions. The mixtures' dynamic properties were studied by analyzing the hydrogen bond, ion-pair, and ion-cage lifetimes of the system. Monoethanolammonium and triethanolammonium ILs show different types of spatial distribution functions. The cations have lesser effect on dynamics compared with anions. The charge on the anion greatly affects the dynamics of mixtures. The dianion mixtures show slower dynamics than the monoanionic mixtures. The hydrogen bonding between cations and anions is stronger than that between cations and neutral molecules due to strong coulombic attractive forces. The cations spend more time around the dianions as compared to monoanions. The distributions of voids show that the void sizes are smaller in triethanolamine-based mixtures. The sulfobenzoate-based mixtures show voids smaller than those of pyridine-3-carboxylate-based mixtures due to more available free space between the entities, which facilitates the overall dynamics.

Predicting Thermal Decomposition Temperature of Binary Imidazolium Ionic Liquid Mixtures from Molecular Structures.

Ionic liquids (ILs) have been regarded as “designer solvents” because of their satisfactory physicochemical properties. The 5% onset decomposition temperature (Td,5%onset) is one of the most conservative but reliable indicators for characterizing the possible fire hazard of engineered ILs. This study is devoted to develop a quantitative structure–property relationship model for predicting the Td,5%onset of binary imidazolium IL mixtures. Both in silico design and data analysis descriptors and norm index were employed to encode the structural characteristics of binary IL mixtures. The subset of optimal descriptors was screened by combining the genetic algorithm with the multiple linear regression method. The resulting optimal prediction model was a four-variable multiple linear equation, with the average absolute error (AAE) for the external test set being 12.673 K. The results of rigorous model validations also demonstrated satisfactory model robustness and predictivity. The present study would provide a new reliable approach for predicting the thermal stability of binary IL mixtures.

Influence of thermodynamically inconsistent data on modeling the solubilities of refrigerants in ionic liquids using an artificial neural network

In this work, a general thermodynamic consistency test is applied to analyze phase equilibrium data (PTx) for binary refrigerant and ionic liquid mixtures. The Valderrama-Patel-Teja (VPT) equation of state and the Kwak and Mansoori (KM) mixing rules are employed to correlate the solubility data of several refrigerants in different ionic liquids, and the Gibbs-Duhem equation is employed to check the thermodynamic consistency of six hundred forty-two experimental data points. The main purpose of this work is to analyze the influence of experimental data that are declared thermodynamically inconsistent on modeling the solubilities of refrigerants in ionic liquids using an artificial neural network. The results obtained via the test are classified into three categories: thermodynamically consistent, not fully consistent and thermodynamically inconsistent. Subsequently, a multilayer perceptron is trained to predict solubility in three cases: i) learning with isotherms that are declared thermodynamically consistent; ii) learning with isotherms, including those that are declared thermodynamically consistent and those that are not fully consistent; and iii) learning with all isotherms, even those that are declared thermodynamically inconsistent. For each case, the architecture, input combination and number of parameters necessary to achieve reasonable predictions are determined. The results show that the use of thermodynamically consistent and not fully consistent data is sufficient for finding an artificial neural network with a reasonable number of parameters.

Surface tension of binary mixtures containing environmentally friendly ionic liquids: Insights from artificial intelligence

The surface tension (ST) of ionic liquids (ILs) and their accompanying mixtures allows engineers to accurately arrange new processes on the industrial scale. Without any doubt, experimental methods for the specification of the ST of every supposable IL and its mixtures with other compounds would be an arduous job. Also, experimental measurements are effortful and prohibitive; thus, a precise estimation of the property via a dependable method would be greatly desirable. For doing this task, a new modeling method according to artificial neural network (ANN) disciplined by four optimization algorithms, namely teaching–learning-based optimization (TLBO), particle swarm optimization (PSO), genetic algorithm (GA) and imperialist competitive algorithm (ICA), has been suggested to estimate ST of the binary ILs mixtures. For training and testing the applied network, a set of 748 data points of binary ST of IL systems within the temperature range of 283.1–348.15 K was utilized. Furthermore, an outlier analysis was used to discover doubtful data points. Gained values of MSE & R2 were 0.0000007 and 0.993, 0.0000002 and 0.998, 0.0000004 and 0.996 and 0.0000006 and 0.994 for the ICA-ANN, TLBO-ANN, PSO-ANN and GA-ANN, respectively. Results demonstrated that the experimental data and predicted values of the TLBO-ANN model for such target are wholly matched.

Thermodynamic Modeling Of Electrolytic Solutions of Ionic Liquids for Gas Hydrates Inhibition Applications

The formation of hydrates in oil and gas transmission pipelines can cause blockage inside them and disrupt the normal flow. It may cause safety problems along with economic loss. To avoid these problems, it is necessary to have knowledge about gas hydrate formation. In this regard, hydrate liquid vapor equilibrium (HLVE) modeling can prove to be of significance as it predicts the phenomenon accurately. Dickens and Quinby-Hunt model is used to predict HLVE points. The experimental data has been obtained from open literature concerning inhibition of gas hydrates. The electrolytic binary solution mixtures of ionic liquids and quaternary ammonium salts (QAS) with commercial hydrate inhibitors have been taken into consideration. Methanol and mono ethylene glycol (MEG) are commercially used inhibitors. The gases forming hydrates include CO2, CH4 and mixed gas (CO2/CH4/N2). The experimental results are compared with the results obtained through modeling. The results show the applicability of the model as in case of QAS+MEG solution mixture hydrates with CO2, it shows a good fit. The HLVE findings by model for CH4 hydrates with EMIM-Cl+MEG solution mixture showed an average absolute error of less than 1% which is acceptable. The binary solution mixtures of NaCl+MEG, NaCl+MeOH and CaCl2+MeOH with tertiary gas mixture rich in CO2 were also modeled to find and compare the HLVE points from literature. It is found that the selected model is more suitable to be used in low pressure conditions and at high pressure, average absolute error (AAE) between experimental and modeling values is also high. It shows the suitability of the model and it can be further used in case of ionic compounds to predict hydrate inhibition behavior.

Computational study of the structure of ternary ionic liquid/salt/polymer electrolytes based on protic ionic liquids

The stability of binary mixtures of several protic ionic liquids (ethylammonium nitrate, ethylammonium acetate and ethylammonium tetrafluoroborate) with polyethylene oxide is studied by means of molecular dynamics simulations. The solubility range is seen to be wider for ethylammonium acetate, and the structure and single-particle dynamics of its ternary mixtures with lithium acetate are then studied. The structure of liquid mixtures of lithium acetate with the ionic liquid is seen to be seldom modified by the addition of the polymer, with very limited hydrogen bonding between the ionic liquid and the polymer taking place. Moreover, lithium is seen to be solvated in the liquid phase forming [Li(ACE)4]−3 tetrahedral complexes irrespective of the presence of the polymer, with very limited binding of metal cations to oxygen atoms in the polymer backbone. Hence, the registered single particle dynamics and lithium transport takes place in practically the same way as in the liquid phase with almost no interference of the polymer, contrarily to previously reported results for other ionic liquids.

Interactions between 1-butyl-3-methylimidazolium cation with various anions and carboxylic acids: Physicochemical and spectroscopic aspects

In this work, the intermolecular interactions for binary mixtures of ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate with acetic and propionic acid were evaluated through the measurement of thermophysical properties, density (ρ), sound velocity (u), refractive index (nD) and surface tension (γ) at T = (293.15−333. 15) K and p = 0.1 MPa. The experimental results were used to compute the thermodynamic properties of the binary mixtures, which were then fitted to the Redlich−Kister polynomial equation. The FTIR spectra of the pure components and the binary mixtures at an equimolar composition were recorded to confirm results from thermodynamic properties. The variations of the thermodynamic properties with IL mole fraction and temperature and the effect of the IL anion and alkyl length of the carboxylic acid on the thermodynamic properties have been discussed.

A green and highly efficient synthesis of 5-hydroxymethylfurfural from monosaccharides using a novel binary ionic liquid mixture

Abstract We reported the development of 5-hydroxymethylfurfural (HMF) synthesis from monosaccharides using a binary ionic liquid as a reaction medium. Bronsted–Lewis acidic ionic liquid (BLAIL) was synthesized from DABCO, 1,4-butane sultone, and AlCl3 under mild conditions. The BLAIL was found to be a suitable catalyst for the synthesis of HMF from monosaccharides in [Emim]Cl as a solvent. Under the optimized conditions, the yields of the HMF from glucose and fructose were 30.5 % and 96.5 %, respectively. The influence of time, temperature, catalytic loading, and substrate on the reaction was systematically investigated. The binary ionic liquid mixture could be reused three times without a noticeable drop in the activity. The isolation of HMF was easily performed through a liquid-liquid extraction method, which could be applied to the industrial process.

Manganese Fluoride Nanoparticles Synthesized by Microwave Irradiation Using Ionic Liquid–Ethylene Glycol Mixtures: Room-Temperature Photoluminescence, Crystalline Phase, and Morphology

The facile and rapid microwave-assisted method has been demonstrated to be effective in synthesizing manganese fluoride (MnF2) nanoparticles in binary mixtures of ethylene glycol and imidazolium-based ionic liquid containing fluorine, within a minute, without any surfactant and stabilizer. The effect of volume ratio of an ionic liquid in the binary mixtures with ethylene glycol and the length of the alkyl chain of imidazolium on the morphologies and crystalline structures of MnF2 was investigated. Two types of crystalline phases MnF2, P42/mnm rutile and P4̅2m space group, were synthesized depending on the volume ratio of EMIM BF4. The morphologies of rutile MnF2 clearly varied depending on what kind of ionic liquid was used in the synthesis. MnF2 nanoparticles and spherical nanoclusters assembled by nanospheres were synthesized when the used ionic liquid was OMIM BF4 and EMIM BF4, respectively. Clear room temperature photoluminescence (PL) spectra of MnF2 nanoparticles were observed at ambient pressure. The change of PL spectra depending on the crystalline phase was also observed. In this study, we report that the microwave-assisted method using ethylene glycol–ionic liquid binary mixtures is proper for synthesizing high-quality MnF2 nanoparticles with controllable crystalline phase and morphology.

Insights on the speed of sound in ionic liquid binary mixtures: Investigation of influential parameters and construction of predictive models

Relative novelty and wide functionality of ionic liquids (ILs) have led to a surge in the studies devoted to experimental determination of their physicochemical properties. Systematic collection and analysis of the available data and development of predictive models to address the extreme diversity of IL systems are of great value in this regard. In the present work, the significance of speed of sound in ILs and their mixtures was outlined and related theoretical concepts were surveyed. A comprehensive database was utilized for the construction of predictive models based on least square support vector machine. By constructing four different models, the influence of temperature, molecular weight, and mole fraction of the components, as well as density, speed of sound, and surface tension of each in their pure form at atmospheric pressure and room temperature was explored in detail. Comparative evaluation of the models indicated that all performed fairly well (best R2 = 0.9965) with different cost-accuracy trade-offs. Further investigations regarding the proticity of the mixture components and their relative concentration enabled us to identify the major factors in deviation of the models from expected values. Accordingly, omitting the water-containing and pure non-IL data points led to a considerable improvement in all models (best R2 = 0.9994), indicating the particular suitability of the models for nonaqueous binary mixtures with x > 0. This study is believed to provide insights for future research on physicochemical properties in IL mixture systems.

Thermophysical Properties of 1-Octyl-3-Methylimidazolium Acetate with Organic Solvents

Ionic liquid (IL) usually possesses high viscosity. In this work, the selected organic solvents, namely, dimethyl sulfoxide, N,N-dimethylacetamide, and N,N-dimethylformamide, were used as the diluents to lower IL viscosity. The thermophysical properties of the densities and viscosities for the binary mixtures of IL (i.e., 1-octyl-3-methylimidazolium acetate) with solvents were studied at normal pressure in the temperature ranges of 303.15 K to 348.15 K. The effects of the organic solvents on lowering IL viscosity were quantitatively evaluated. The excess properties of the mixtures were calculated to analyze the interactions between IL and solvents. The hard-sphere model was employed to reproduce the viscosity behavior of the pure substances and binary mixtures.

Application of gene expression programming for predicting density of binary and ternary mixtures of ionic liquids and molecular solvents

Ionic Liquids (ILs) have received increased attention across a number of disciplines in recent years. This noticeable importance of ILs is attributed to their attractive proprieties. Precise evaluation of the thermophysical properties of ionic liquids and their mixtures with molecular solvents is essential for distinct multidisciplinary applications. In this study, a rigorous white-box intelligent technique, viz. gene expression programming (GEP) was implemented for establishing new correlations for accurate prediction of density of binary and ternary mixtures of ILs and molecular solvents. The newly suggested correlations were developed using a comprehensive experimental database with 1985 real measurements under a variety of operational conditions. The obtained results revealed that the newly established GEP-based correlations can predict the density of binary and ternary mixtures of ILs and molecular solvents with a high degree of integrity. The GEP-based correlations exhibited overall average absolute relative error (AARE) values of 0.5621% and 0.2128% for binary and ternary cases, respectively. Besides, it was found that our proposed explicit correlations followed the expected tendency with respect to the considered variables. Furthermore, the superiority and the reliability of the GEP-based correlations was testified against the best-existing approaches in the literature. Finally, the leverage approach was performed and the statistical validity of the correlations and the experimental data was testified.

Synergistic/antagonistic cytotoxic effects in mixtures of ionic liquids with doxorubicin or mitoxantrone

An NMR spectroscopy study of ionic liquid/drug systems at a molecular level and a scanning electron microscopy study in the liquid phase at a nano-scale level were applied for the first time to study ionic preparations of well-known anticancer drugs. Cytotoxicity of binary mixtures of imidazolium ionic liquids with doxorubicin or mitoxantrone was studied in human colorectal adenocarcinoma CaCo-2 cells, and the evidence of synergism/antagonism was assessed. Of the ten drug-containing mixtures tested, four demonstrated significant synergistic or antagonistic cytotoxic effects. These mixtures revealed distinct micro-structured patterns, as shown by scanning electron microscopy, whereas nuclear magnetic resonance evidenced the formation of strong interactions between the drug and the ionic liquid in some of the mixtures. Notably, all the test substances induced the cell death via necrosis in the CaCo-2 cell line, thus revealing the dependence of the observed cytotoxic effects on the cell type. The observed synergistic effects suggested possible benefits of applying ionic liquids in drug formulations.

(Invited) Evolution of Structural, Transport and Electrical Properties of Binary Ionic Liquids in the Presence of Graphite

The flexibility to manipulate various interactions in ionic liquids by changing the cation, anion, or the various functional groups on the ions has drawn researchers to design tailor-made ionic liquids for a given application. Another approach that is gaining importance in tuning the properties of ionic liquids is to form binary, ternary, and reciprocal ionic liquid mixtures. Results from molecular simulations conducted in our research group have demonstrated that the binary ionic liquid mixtures in which two anions are combined in different molar ratios for a given cation can lead to either native or non-native structures in the bulk depending on the difference between the hydrogen bonding ability of the participating anions. The non-native structures differ markedly from those for the pure ionic liquid analogues and impact the physical dissolution mechanism for gases such as CO2.Given the importance of ionic liquids as electrolytes in the next-generation of batteries, it is likely that such ionic liquid mixtures will increasingly be investigated for their ability to transport ions to and from charged surfaces. However, very little is currently known regarding how the presence of a surface or an interface affects the local and long-range structures of binary ionic liquids. In this talk, we will present our findings from molecular simulation studies by examining the structural response of binary ionic liquid mixtures comprised of a single cation in combination with two anions when presented with a graphite surface. We will compare and contrast these structures to those obtained when binary ionic liquid mixtures are formed with a single anion and two cations and a graphite surface is introduced. Additionally, we will elucidate the influence of graphite on the transport and electrical properties of binary ionic liquids.

Molecular-level insights into composition-dependent structure, dynamics, and hydrogen bonds of binary ionic liquid mixture from molecular dynamics simulations

In this work, we have performed a series of molecular dynamics (MD) simulations to explore structure, dynamics, and hydrogen bonds (HBs) of the imidazolium-based ionic liquid (IL) mixture containing [Emim][BF4]x[NTF2](1−x), where the molar fraction x is 0.0, 0.25, 0.50, 0.75, and 1.0, respectively. Our simulation results demonstrate that the association extent between cations and both anions become weaker and weaker as the concentration of [BF4]− anion increases due to the weakened interactions between them. Meanwhile, all ions in the IL mixture are found to diffuse faster at the higher concentration of [BF4]− anion while the order of diffusion rate is always [Emim]+ > [BF4]– > [NTF2]− owing to different molecular weights regardless of the composition. Furthermore, the weakened HBs between cations and anions are found to be at the higher concentration of [BF4]− anion, leading to a faster rotation for all ions in the IL mixture. Compared to the diffusion rates among different ions, however, there is unexpectedly a much larger difference in their rotation rates with the fixed order of [BF4]– > [Emim]+ > [NTF2]−, where the rotational relaxation times of [Emim]+ and [NTF2]− are much more than that of [BF4]– by at least one order of magnitude. This can be attributed to that the rotational motions of spherical [BF4]– anions only require the transient HB breakage with cations so that their rotations should be affected by the continuous HB strength, which is significantly different from those of both [Emim]+ and [NTF2]− dominated by the intermittent HB strength. Our simulation results provide a molecular-level understanding composition-dependent structure, dynamics, and HBs in IL mixtures.