Binary Ionic Mixtures Research Articles

Determination of the Solute Content and Volumetric Properties of Binary Ionic Liquid Mixtures Using a Global Regularity of Molar Volume Expansion

Determination of the Solute Content and Volumetric Properties of Binary Ionic Liquid Mixtures Using a Global Regularity of Molar Volume Expansion

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.

Analytic models for interdiffusion in dense plasma mixtures

The characteristics of atomic-scale mixing are determined by diffusive processes driven by gradients. One such process is interdiffusion, a process driven by density gradients. We consider the various options for formulating interdiffusion in terms of Green–Kubo autocorrelation functions and the thermodynamic factor. Through models for the direct correlation function, we generalize expressions for the thermodynamic factor to include different electron and ion temperatures, electron degeneracy, finite-temperature exchange, and strong coupling. Additionally, a Gaussian autocorrelation function (GAF) is employed for a binary ionic mixture, yielding a simple analytic transport model for interdiffusion. The GAF model is shown to be accurate for moderately and strongly coupled plasmas.

Relaxation of strongly coupled binary ionic mixtures in the coupled mode regime

Understanding ion transport in plasma mixtures is essential for optimizing the energy balance in high-energy-density systems. In this paper, we focus on one transport property, ion–ion temperature relaxation in a strongly coupled plasma mixture. We review the physics of temperature relaxation and derive a general temperature relaxation equation that includes dynamical correlations. We demonstrate the fidelity of three popular kinetic models that include only static correlations by comparing them to data from molecular dynamics simulations. We verify the simulations by comparing with laboratory data from ultracold neutral plasmas. By comparing our simulations with high fidelity kinetic models, we reveal the importance of dynamical correlations in collisional relaxation processes. These correlations become increasingly significant as the ion mass ratio in a binary mixture approaches unity.

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.

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.

(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.

Surface Propensity of Anions in a Binary Ionic-Liquid Mixture Assessed by Full-Range Angle-Resolved X-ray Photoelectron Spectroscopy and Surface-Tension Measurements.

Angle-resolved X-ray photoelectron spectroscopy and contact-angle measurements guided by a signal attenuation model are utilized to extract molar composition and anion enrichment in the vacuum interface of a binary ionic liquid mixture, having a common quaternary ammonium cation and two different anions. By using the intensity ratio of the F1s peaks belonging to the two different anions recorded at the full electron take-off angle range, from 0° to 80°, we have determined that only a fractionally covered and anion enriched surface layer can predict the AR-XPS data, which is also consistent with surface tension measurements. Moreover, the more bulky and non-spherical anion enrichment is evident even at the conventional and the so assumed bulk sensitive take-off angle of 0°. This methodology provides a surface enrichment factor of the molecular ions and clearly serves as an experimental evidence for recently debated surface layering and/or island structure in ionic liquid systems.

Evaluating diffusion and the thermodynamic factor for binary ionic mixtures

Molecular dynamics (MD) simulations are a powerful tool for the calculation of transport properties in mixtures. Not only are MD simulations capable of treating multicomponent systems, they are also applicable over a wide range of temperatures and densities. In plasma physics, this is particularly important for applications such as inertial confinement fusion. While many studies have focused on the effect of plasma coupling on transport properties, here we focus on the effects of mixing. We compute the thermodynamic factor, a measure of ideal/non-ideal mixing, for three binary ionic mixtures. We consider mixtures of hydrogen and carbon, hydrogen and argon, and argon and carbon, each at 500 randomly generated state points in the warm dense matter and plasma regimes. The calculated thermodynamic factors indicate different mixing behavior across phase space, which can significantly affect the corresponding mutual diffusion coefficients. As MD simulations are still computationally expensive, we apply modern data science tools to predict the thermodynamic factor over a large phase space. Further, we propose a more accurate approximation to the mutual diffusion coefficient than the commonly applied Darken relation.

Differentiation and Quantification of Diastereomeric Pairs of Glycosphingolipids Using Gas-Phase Ion Chemistry.

Glycosphingolipids (GSLs), including lyso-glycosphingolipids (lyso-GSLs) and cerebrosides (HexCer), constitute a sphingolipid subclass. The diastereomerism between their monosaccharide head groups, glucose and galactose in mammalian cells, gives rise to an analytical challenge in the differentiation of their biological roles in healthy and disease states. Shotgun tandem mass spectrometry has been demonstrated to be a powerful tool in lipidomics analysis in which the differentiation of the diastereomeric pairs of GSLs could be achieved with offline chemical modifications. However, the limited number of standards, as well as the lack of the comprehensive coverage of the GSLs, complicates the qualitative and quantitative analysis of GSLs. In this work, we describe a novel strategy that couples shotgun tandem mass spectrometry with gas-phase ion chemistry to achieve both differentiation and quantification of the diastereomeric pairs of GSLs. In brief, deprotonated GSL anions, [GSL-H]-, and terpyridine-magnesium complex dications, [Mg(Terpy)2]2+, are sequentially injected and mutually stored in a linear ion trap to form charge-inverted complex cations, [GSL-H + MgTerpy]+. The collision-induced dissociation of the charge-inverted complex cations leads to significant spectral differences between the diastereomeric pairs of GSLs, which permits their distinction. Moreover, we describe a relative quantification strategy with the normalized %Area extracted from selected diagnostic ions in binary mixtures. Analytical performance with the selected pure-component pairs, lyso-GSLs and HexCer(d18:1/18:0), was also evaluated in terms of accuracy, repeatability, and interday precision. The pure components could be extended to different fatty acyl chains on cerebrosides with a limited error, which allows for the relative quantitation of the diastereomeric pairs without all standards. We successfully applied the presented method to identify and quantify, on a relative basis, the GSLs in commercially available total cerebroside extracts from the porcine brain.

Macroscopic Differentiators for Microscopic Structural Nonideality in Binary Ionic Liquid Mixtures.

Combining two ionic liquids to form a binary ionic liquid mixture is a simple yet effective strategy to not only expand the number of ionic liquids but also precisely control various physicochemical properties of resultant ionic liquid mixtures. From a fundamental thermodynamic point of view, it is not entirely clear whether such mixtures can be classified as ideal solutions. Given a large number of binary ionic liquid mixtures that emerge, the ability to predict the presence of nonideality in such mixtures a priori without the need for experimentation or molecular simulation-based calculations is immensely valuable for their rational design. In this research report, we demonstrate that the difference in the molar volumes (ΔV) of the pure ionic liquids and the difference in the hydrogen-bonding ability of anions (Δβ) are the primary determinants of nonideal behavior of binary ionic liquid mixtures containing a common cation and two anions. Our conclusion is derived from a comparison of microscopic structural properties expressed in terms of radial, spatial, and angular distributions for binary mixtures and those of the corresponding pure ionic liquids. Molecular dynamics simulations of 16 binary ionic liquid mixtures, containing a common cation 1-n-butyl-3-methylimidazolium [C4mim]+ and combinations of (less basic) fluorinated {trifluoromethylacetate [TFA]-, trifluoromethanesulfonate [TFS]-, bis(trifluoromethanesulfonyl)imide [NTf2]-, and tris (pentafluoroethyl) trifluorophosphate [eFAP]-} versus (more basic) nonfluorinated {chloride Cl-, acetate [OAC]-, methylsulfate [MeSO4]-, and dimethylphosphate [Me2PO4]-} anions, were conducted. The large number of binary ionic liquid mixtures examined here enabled us to span a broad range of ΔV and Δβ values. The results indicate that binary mixtures of two ionic liquids for which ΔV > 60 cm3/mol and Δβ > 0.4 are expected to be microscopically nonideal. On the other hand, ΔV < 60 cm3/mol and Δβ < 0.4 will lead to molecular structures that are not differentiated from those of their pure ionic liquid counterparts.

Binary Mixtures of Aprotic and Protic Ionic Liquids Demonstrate Synergistic Polarity Effect: An Unusual Observation

In this communication, we demonstrate the solute–solvent and solvent–solvent interactions in the binary mixtures of two aprotic ionic liquids, namely 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, with the protic ionic liquid 1-methylimidazolium acetate. The synergistic effects as expressed by the solvatochromic parameter are noted. This observation is in contrast to the mixing of protic ionic liquids 1-methylpyrrolidium acetate and 4-methylmorpholine acetate with 1-methylimidazolium acetate, respectively. It appears that the synergistic effects in the binary mixtures of aprotic and protic ionic liquids are caused by the formation of hydrogen bonds, since cations are dominant H-bond donors while anions are dominant H-bond acceptors. Preferential solvation models are used to describe the solute–solvent interactions in the binary ionic liquid mixtures.

Expedient synthesis of novel antibacterial hydrazono-4-thiazolidinones under catalysis of a natural-based binary ionic liquid.

A library of pyran-2H-one-3-ylmethylidene and chromene-2H-one-3-ylmethylidene derivatives of the titled heterocyclic framework was synthesized from 3-acyl-4-hydroxypyran/chromene-2H-one via sequential reaction with thiosemicarbazide and dialkyl acetylenedicarboxylates. The syntheses were carried out under efficient catalysis of a new binary ionic liquid mixture [L-prolinium chloride][1-methylimidazolium-3-sulfonate] in one pot and solvent-free conditions. Calculations based on density functional theory displayed that the barrier energy for interconversion of the two possible diastereomeric isomers of each product is less than the thermal energy of molecules at room temperature, as only one product can be resolved from a given reaction mixture. This seems to be the case for the previously reported hydrazonothiazolidines. The binary ionic liquid mixture melts at near room temperature and can be considered as a solution of HCl in 1:1 mixture of two zwitterionic species. It proved to be more efficient than its constituents in catalyzing the above synthesis in one-pot operation. Some of the synthesized products have shown pronounced antibacterial activities. The ionic liquid is virtually stable in air and moisture, as can be retrieved several times without appreciable decrease in its catalytic activity.

Extraction of phenols from coal tar oil using binary solvents and ionic liquid mixture

The extraction of phenols from coal tar oils using acetonitrile solutions of ionic liquids (ILs) through a new extraction method is studied. The IL containing acetonitrile solution formed a clear immiscible layer with hexane containing coal tar oil, which facilitated superior extractions of phenol and p-cresol with high distribution coefficient values. The IL with lower carbon chain length (three carbons) showed extraction efficiency greater than 96% for phenol and p-cresol extractions from coal tar oil. The process models for extraction of phenol and p-cresol from coal tar oil were studied to comprehend the interactions of various factors. [Received: December 23, 2017; Accepted: March 7, 2018]

Extraction of phenols from coal tar oil using binary solvents and ionic liquid mixture

The extraction of phenols from coal tar oils using acetonitrile solutions of ionic liquids (ILs) through a new extraction method is studied. The IL containing acetonitrile solution formed a clear immiscible layer with hexane containing coal tar oil, which facilitated superior extractions of phenol and p-cresol with high distribution coefficient values. The IL with lower carbon chain length (three carbons) showed extraction efficiency greater than 96% for phenol and p-cresol extractions from coal tar oil. The process models for extraction of phenol and p-cresol from coal tar oil were studied to comprehend the interactions of various factors. [Received: December 23, 2017; Accepted: March 7, 2018]

Mesoscale Organization and Dynamics in Binary Ionic Liquid Mixtures.

The impact of mesoscale organization on dynamics and ion transport in binary ionic liquid mixtures is investigated by broad-band dielectric spectroscopy, dynamic-mechanical spectroscopy, X-ray scattering, and molecular dynamics simulations. The mixtures are found to form distinct liquids with macroscopic properties that significantly deviate from weighted contributions of the neat components. For instance, it is shown that the mesoscale morphologies in ionic liquids can be tuned by mixing to enhance the static dielectric permittivity of the resulting liquid by as high as 100% relative to the neat ionic liquid components. This enhancement is attributed to the intricate role of interfacial dynamics associated with the changes in the mesoscopic aggregate morphologies in these systems. These results demonstrate the potential to design the physicochemical properties of ionic liquids through control of solvophobic aggregation.

Competition of mixed divalent ions through supported liquid membranes: Co-ion and concentration effects on permeability

Zn2+, Cu2+ and Ni2+ permeabilities through supported liquid membranes (SLMs) were determined experimentally from single, binary, and ternary ionic mixtures. Microporous polypropylene membrane was used as the frame to retain isopar-L solvent and di (2-ethylhexyl) phosphoric acid (D2EHPA) carrier. Sulfuric acid solution was used as a strip (receiving) solution. The ion permeability values were in the 10−7-10−6 cm2 s−1 range and increased with the concentrations of D2EHPA in isopar-L and the stripping sulfuric acid. The ion ideal selectivity ranged from 1.05 (Zn/Cu) to 8.40 (Zn/Ni), depending on the feed concentration. The single ion permeability was significantly higher than the binary mixtures, probably due to ion competition with D2EHPA carrier molecules. High selectivity was achieved using ternary mixtures: Zn2+ was the fast-permeating species due to preferential sorption with D2EHPA. Separating Zn2+ from Cu2+ and/or Ni2+ mixtures was most efficient with high D2EHPA concentration, concentrated H2SO4 strip solution, concentrated feed solution, and from multiple ionic mixes.

Effect of electrostatic interactions on the relaxation dynamics of pharmaceutical eutectics

In this paper, we investigate the temperature-dependent relaxation dynamics in the glassy and supercooled liquid state of dipolar and ionic eutectic mixtures made of two anesthetic agents (lidocaine and prilocaine) and their hydrochloride salts, respectively. In addition to eutectic phases containing 1:1 and 4:1 mol/mol of LD/PRL and LD-HCl/PRL-HCl, respectively, the relaxation properties of non-eutectic compositions and parent compounds are also studied. We found that electrostatic long-range forces determine strongly the dielectric and mechanical response of eutectic material. As a result of Coulomb interactions between ion pairs, an additional β-relaxation mode was found in the dielectric spectra of glassy LD-HCl/PRL-HCl mixtures. On the other hand, the studies of relaxation dynamics of ionic and non-ionic mixtures at T > Tg revealed a continuous decrease of both fragility mP and the length scale of dynamic heterogeneity NαB(Tg), with simultaneous growth of Tg, when the electrostatics forces appear. At the same time, we found the charge transport being decoupled from structural dynamics in all studied ionic binary mixtures that is due to the fast proton hopping. However, the efficiency of proton transport is dropping down with an increase of Tg.

Enhancement factor of nuclear reactions in partially ionized plasmas and asymmetric mixtures

When hydrogen is mixed with heavy (high‐Z) elements, even as traces, such as iron in the sun, the plasma mixture transits from a weakly coupled state to the intermediate coupling regime of simultaneous weak and strong couplings due to charge asymmetry. In those circumstances, partial ionization is an important aspect to consider. We present a global approach for evaluating enhancement factors for thermonuclear reactions in such mixtures. We grounded our approach on extensive orbital free molecular dynamics (OFMD) simulations of hydrogen‐silver mixtures, chosen as a prototype of hydrogen—high‐Zmixtures, in a large range of temperature (100 &lt; T &lt; 1600 eV). By comparing a series of OFMD simulations to hyper‐netted chain calculations of effective binary ionic mixtures (eBIM), we set a general procedure for computing enhancement factors. The electron screening contribution is also included implicitly in the definition of the effective ionizations within the average atom framework. The agreement between the pair distribution functions of OFMD and eBIM validates a prescription in which each average atom representing a given species shares the same external electron density with the others (iso‐nerule). We checked that an interpolation formula between weak and strong couplings in BIM, due to Chugunov and DeWitt, is accurate enough to address the limit of extreme dilution of a heavy element.