Mixtures Of Imidazolium-based Ionic Liquids Research Articles

Design and Characterization of Epoxy Resin Systems Based on Mixtures of Imidazolium-Based Ionic Liquids with Docusate and Dicyanamide Anions

This study focuses on the synthesis, characterization, and application of four ionic liquids (ILs), three of which are being reported for the first time, with unique thermal properties and diverse anion-cation combinations, specifically in the context of epoxy resin polymerization. 1-3-Didodecylimidazolium dicyanamide (dDDIM DCA), 1-3-Didodecylimidazolium docusate (dDDIM DOSS), 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA), and 1-ethyl-3-methylimidazolium docusate (EMIM DOSS) were used to prepare six different mixtures with the same cation and with varying concentrations of DCA components, which is the main factor of an efficient polymerization, while the other component is intended to modify the properties of the cured resin. Mixtures based on EMIM cation demonstrated increased enthalpy and lower onset polymerization temperatures, indicating more efficient curing processes. The hardness of cured epoxy resins can be adjusted by altering the curing temperature and IL composition, with EMIM DCA and EMIM DOSS mixtures displaying high Shore A hardness, suitable for durable surface applications. In contrast, mixtures with higher dDDIM DCA proportions offered a balance between rigidity and flexibility, ideal for applications requiring both mechanical strength and elasticity.

Reversible phase transition poly(benzyl methacrylate)/ionic liquid electrolytes for effective overheating protection in lithium batteries

Battery safety is influenced by various factors, with thermal runaway being one of the most significant concerns. While most studies have concentrated on developing one-time, self-activating mechanism for thermal protection, such as temperature-responsive electrodes, and thermal-shutdown separators, these methods only provide irreversible protection. Recently, reversible temperature-sensitive electrolytes have emerged as promising alternatives, offering both thermo-reversibility and self-protective properties. However, further research is crucial to fully understand these thermal-shutdown electrolytes. In this study, we propose lower critical solution temperature (LCST) phase behavior poly(benzyl methacrylate)/imidazolium-based ionic liquid mixtures to prepare temperature-sensitive electrolytes that provide reversible thermal shutdown protection of batteries. This electrolyte features an appropriate protection temperature (∼105°C) and responds quickly within a 1 min at 105°C, causing cells to hardly discharge as the voltage suddenly drops to 3.38 V, and providing efficient thermal shutdown protection within 30 min. Upon cooling back to room temperature, the battery regains its original performance. Additionally, the electrolyte exhibits excellent cycling stability with the capacity retention of the battery is 91.6% after 500 cycles. This work provides a viable solution for preventing batteries from thermal runaway triggered by overheating.

Insight to the Local Structure of Mixtures of Imidazolium-Based Ionic Liquids and Molecular Solvents from Molecular Dynamics Simulations and Voronoi Analysis.

While the physicochemical properties as well as the NMR and vibration spectroscopic data of the mixtures of ionic liquids (ILs) with molecular solvents undergo a drastic change around the IL mole fraction of 0.2, the local structure of the mixtures pertaining to this behavior remains unclear. In this work, the local structure of 12 mixtures of 1-butyl-3-methylimidazolium cation (C4mim+) combined with perfluorinated anions, such as tetrafluoroborate (BF4-), hexafluorophosphate (PF6-), trifluoromethylsulfonate (TFO-), and bis(trifluoromethanesulfonyl)imide, (TFSI-), and aprotic dipolar solvents, such as acetonitrile (AN), propylene carbonate (PC), and gamma butyrolactone (γ-BL) is studied by molecular dynamics simulations in the entire composition range, with an emphasis on the IL mole fractions around 0.2. Distributions of metric properties corresponding to the Voronoi polyhedra of the particles (volume assigned to the particles, local density, radius of spherical voids) are determined, using representative sites of the cations, anions, and the solvent molecules, to characterize the changes in the local structure of these mixtures. By analyzing the mole fraction dependence of the average value, fluctuation, and skewness parameter of these distributions, the present study reveals that, around the IL mole fraction of 0.2, the local structure of the mixture undergoes a transition between that determined by the interionic interactions and that determined by the interactions between the ions and solvent molecules. It should be noted that the strength of the interactions between the ions and the solvent molecules, modulated by the change in the composition of the mixture, plays an important role in the occurrence of this transition. The signature of the change in the local structure is traced back to the nonlinear change of the mean values, fluctuations, and skewness values of the metric Voronoi polyhedra distributions.

Noble Metals Dissolution Catalyzed by [AlCl4 -]-Based Ionic Liquids.

Imidazolium-based ionic liquid mixtures with [NO3]- and [AlCl4]- anions were used as oxidizing agents for the dissolution of Au, Pd, and Pt metals under mild conditions. The thermodynamic reduction of [NO3]- to [NO] is catalyzed by [AlCl4]- anions and coupled with the oxidation process of noble metals. The developed ionic liquid system for dissolving Au can reactivate the Au0 formed in the deactivation process of the catalyst in vinyl chloride production. This demonstrates the relevance of the here-presented work for technical noble metal recycling.

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.

Molecular-level behavior of imidazolium-based ionic liquid mixtures

Understanding the molecular-level organization of anions and cations in a mixture of different ionic liquids (ILs) is challenging, but it can be very important for designing solvents and IL-based membrane materials. Here, we perform all-atom molecular dynamics (MD) simulations to understand the intermolecular interactions and structuring of both neat and mixed IL compositions containing 1-benzyl-3-methylimidazolium [ZMIM+], 1-butyl-3-methylimidazolium [BMIM+], bistriflimide [Tf2N−], and tetrafluoroborate [BF4−]. We observe very strong underlying molecular-level migrations in these mixtures, and this tends to mainly involve the anion species. As compared to the systems with a single anion, the mixed anions lead to large increases/decreases in the radial distribution function peak heights, whereas the cation mixing is relatively benign. The [BF4−] anions have a strong tendency to displace the [Tf2N−] anions in the mixtures, and this is seen with respect to both [BMIM+] and [ZMIM+].

Electrical Conductivities and Interactions in Binary Mixtures of Imidazolium-Based Ionic Liquids with Acetonitrile and Dimethyl Sulfoxide

This paper reports experimental electrical conductivities data of eight binary systems of four ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim][BF4], 1-hexyl-3-methylimidazolium tetrafluoroborate, [Hmim][BF4], 1-butyl-3-methylimidazolium hexafluorophosphate, [Bmim][PF6] and 1-butyl-2,3-dimethyl-imidazolium tetrafluoroborate, [Bmmim][BF4] with the organic solvents dimethyl sulfoxide (DMSO) and acetonitrile (ACN) at atmospheric pressure and temperatures from 298.15 to 328.15 K. It was found that conductivities in the investigated ionic liquids follow the order: [Bmim][BF4] ] [Bmim][PF6] ][Bmmim][BF4] ] [Hmim][BF4]. Experimental results demonstrate that the binary mixtures possess higher electrical conductivity compared with pure components. Electrical conductivity data were correlated using Casteel�Amis and Arrhenius equations. The molar conductivity was derived from experimental data and fitted to Walden rule. The influence of the cation structure and anion type on the conductivity was discussed, which help understanding the intermolecular interactions in the binary systems. A deeper understanding of the transport behavior of ILs is given by means of density functional theory calculations (DFT)

Translational Diffusion in a Set of Imidazolium-Based Ionic Liquids [bmim]+A- and Their Mixtures with Water.

As the development of the work (J. Phys. Chem. B 2019, 123 (10), 2362-2372), we have investigated the translational mobility in the same set of dried imidazolium-based ionic liquids (ILs) [bmim]A (A = BF4-, NO3-, TfO-, I-, Br-, and Cl-) in a wide temperature range using the NMR technique. It is shown that for the [bmim]+ cation, the temperature dependencies of product Dη do not follow the Stokes-Einstein relation for most systems studied, that is, the so-called "diffusion-viscosity decoupling" was realized. The correlation between local and translational mobility in pure IL of the [bmim][A] type was investigated using the data on NMR relaxation rates and diffusion coefficients. The most recent hypothesis of "water pockets" in mixtures of IL with water is critically discussed. Considering the totality of data in the literature and obtained here, we propose a specific model of the microstructure which may be applied up to water concentrations of 80-90 mol % (the structure of water-rich solutions is out of our current consideration). To confirm the model, molecular dynamics simulations of "IL-water" mixtures were also carried out.

Distance Angle Descriptors of the Interionic and Ion-Solvent Interactions in Imidazolium-Based Ionic Liquid Mixtures with Aprotic Solvents: A Molecular Dynamics Simulation Study.

The aim of this paper is to quantify the changes of the interionic and ion-solvent interactions in mixtures of imidazolium-based ionic liquids, having tetrafluoroborate (BmimBF4), hexafluorophosphate (BmimPF6), trifluoromethylsulfonate (BmimTFO), or bis(trifluoromethanesulfonyl)imide (BmimTFSI), anions, and polar aprotic molecular solvents, such as acetonitrile (AN), γ-butyrolactone (GBL), and propylene carbonate (PC). For this purpose, we calculate, using the nearest-neighbor approach, the average distance between the imidazolium ring H atom in positions 2, 4, and 5 (H2,4,5) and the nearest high-electronegativity atom of the solvent or anion (X) as distance descriptors, and the mean angle formed by the C2,4,5-H2,4,5 bond and the H2,4,5···X axis around the H2,4,5 atom as angular descriptors of the cation-anion and cation-solvent interactions around the ring C-H groups. The behavior of these descriptors as a function of the ionic liquid mole fraction is analyzed in detail. The obtained results show that the extent of the change of these descriptors with respect to their values in the neat ionic liquid depends both on the nature of the anion and on the mixture composition. Thus, in the case of the mixtures of the molecular solvents with BmimBF4 and BmimTFO, a small change of the distance and a drastic increase of the angular descriptor corresponding to the cation-anion interactions are observed with decreasing mole fraction of the ionic liquid, indicating that the anion moves from the above/below position (with respect to the imidazolium ring plane) to a position that is nearly linearly aligned with the C2-H2 bond and hinders the possible interaction between the C2-H2 group and the solvent molecules. On the other hand, in the case of mixtures of BmimTFSI and BmimPF6 with the molecular solvents, both the observed increase of the distance descriptor and the slight change of the angular descriptor with decreasing ionic liquid mole fraction are compatible with the direct interactions of the solvent with the C2-H2 group. The behavior of these descriptors is correlated with the experimentally observed 1H chemical shift of the C2-H2 group and the red shift of the C2-H2 vibrational mode, particularly at low ionic liquid mole fractions. The present results are thus of great help in interpreting these experimental observations.

Phase Behavior of Imidazolium-Based Ionic Liquid + Phosphonium-Based Ionic Liquid Mixtures with a Common Anion: Effects of the Alkyl-Chain Length of Cation

The phase behavior of imidazolium-based ionic liquid (IL) + phosphonium-based IL binary mixtures with a common anion has been investigated in the temperature range 253–453 K. Bis(trifluoromethanesulfonyl)amide ([NTf2]−) and tetrafluoroborate ([BF4]−) were selected as common anions. The imidazolium-based IL + phosphonium-based IL mixtures with a common anion showed an upper critical solution temperature (UCST). The phase separation temperatures of the mixtures decreased with increasing alkyl-chain length of the imidazolium cation. In contrast, the phase separation temperatures of the mixtures increased as the alkyl-chain length of the phosphonium cation increased. The phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with [BF4]− as a common anion were remarkably higher than those with [NTf2]−.

イミダゾリウム系イオン液体-水混合溶液中のN-Methylacetamideの低温誘起構造変化

イミダゾリウム系イオン液体-水混合溶液中のN-Methylacetamideの低温誘起構造変化

Influence of Aprotic Cosolvents on the Thermophysical Properties of Imidazolium-Based Ionic Liquid

Imidazolium-based ionic liquids (ILs) have been widely investigated in the biofuels process. In this work, the experimental densities and viscosities of binary mixtures of IL, 1-octyl-3-methylimidazolium chloride, with aprotic cosolvents (i.e., N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and pyridine) were studied at temperatures ranging from (303.15 to 353.15) K at atmospheric pressure. The Vogel–Fulcher–Tammann equation is used to correlate the viscosity data. Toward further understanding the influences of cosolvents on the properties of IL, the excess properties of density and viscosity deviations are calculated as well as the energy barrier. The effects of cosolvents on the density and viscosity are discussed.

Competition between Cation–Solvent and Cation–Anion Interactions in Imidazolium Ionic Liquids with Polar Aprotic Solvents

The subtle interplay between ion solvation and association was analyzed in mixtures of imidazolium-based ionic liquids (ILs) with polar aprotic solvents. A site-specific pattern of cation-solvent and cation-anion interactions was disclosed by a careful analysis of the 1 H and 13 C NMR chemical shift dependence of the mixture composition. It was established that the less polar but more donating γ-butyrolactone is more prone to establish H-bonds with the imidazolium-ring hydrogen atoms of the IL cations than propylene carbonate, particularly at the H2 site and at high dilutions xIL <0.1. The H2 site was found to be more sensitive to intermolecular interactions compared to H4, 5 in the case of ILs with asymmetric anions like trifluoromethanesulfonate (TfO- ) or bis(trifluoromethylsulfonyl)amide (TFSA- ).

Understanding Polymorphic Control of Pharmaceuticals Using Imidazolium-Based Ionic Liquid Mixtures as Crystallization Directing Agents

Imidazolium-based room temperature ionic liquids (RTILs) were tested to assess their ability to control molecular polymorphic behavior. Mixtures of RTILs with distinct cation/anion combinations revealed promising capabilities in directing the crystallization process toward less stable polymorphs. In our tests, gabapentin (GBP) neuroleptic drug was used as a case study, as it is a well know polymorphic active pharmaceutical ingredient. For the first time, pure “bulk” GBP Form IV, a highly unstable polymorph, was isolated through RTILs. Forms were maintained over time, once they were kept soaked, opening new perspectives for the method presented here. Molecular dynamics (MD) simulations clearly supported the results. In this work the polymorphic behavior of GBP is controlled recurring to the use of different pure imidazolium-based RTILs or mixtures, as crystallization solvents. Molecular dynamics simulations clearly supported the results showing that specific H(acidic(C4/C6mim))···O(carboxylate) interaction...

Interactions of Aqueous Imidazolium-Based Ionic Liquid Mixtures with Solid-Supported Phospholipid Vesicles.

Despite the environmentally friendly reputation of ionic liquids (ILs), their safety has been recently questioned given their potential as cytotoxic agents. The fundamental mechanisms underlying the interactions between ILs and cells are less studied and by far not completely understood. Biomimetic films are here important biophysical model systems to elucidate fundamental aspects and mechanisms relevant for a large range of biological interaction ranging from signaling to drug reception or toxicity. Here we use dissipative quartz crystal microbalance QCM-D to examine the effect of aqueous imidazolium-based ionic liquid mixtures on solid-supported biomimetic membranes. Specifically, we assess in real time the effect of the cation chain length and the anion nature on a supported vesicle layer of the model phospholipid DMPC. Results indicate that interactions are mainly driven by the hydrophobic components of the IL, which significantly distort the layer and promote vesicle rupture. Our analyses evidence the gradual decrease of the main phase transition temperature upon increasing IL concentration, reflecting increased disorder by weakening of lipid chain interactions. The degree of rupture is significant for ILs with long hydrophobic cation chains and large hydrophobic anions whose behavior is reminiscent of that of antimicrobial peptides.

Structural ordering transitions in ionic liquids mixtures

Differential capacitance curves for the electrical double layer (EDL) of mixtures of imidazolium-based ionic liquids (ILs) with a common cation (1-ethyl-3-methylimidazolium, [C 2 MIM] + ) and two different anions (bis(trifuoromethylsulfonyl)imide, [Tf 2 N] − ) and tris(pentafluoroethyl)trifluorophosphate [FAP] − ) were obtained. Sharp peaks in the differential capacitance curves were observed for a small range of mixtures compositions at positive charge densities. The appearance and position on the potential scale of the peaks were found to be dependent on the mixture composition and temperature. The occurrence of these phenomena is interpreted as corresponding to an abrupt change in the EDL structure arrangement as a result of a complex interplay of electrostatic interactions and steric effects. The use of the non-structured mercury electrode allowed to decouple the eventual potential induced restructuring occurring at the double layer from the well-known surface reconstruction effects often reported for ionic liquids in contact with single crystal face electrodes. • Structural EDL transitions in ILs mixtures are followed by an abrupt increase in the differential capacitance curves. • Interfacial structure results from the balance between the short range effects and is also affected by long range forces. • Ubiquitous properties obtained by mixing ionic liquids arise from the competition between these two kinds of interactions.

Conductivity of Ionic Liquids: A Neural Network Approach

A mathematical model based on artificial neural networks (ANNs) has been designed to achieve the estimation of the conductivity of three different binary mixtures containing water and one of the following imidazolium-based ionic liquids: 3-ethyl-methylimidazolium tetrafluoroborate ([emim][BF4]), 3-butyl-methylimidazolium tetrafluoroborate ([bmim][BF4]), and 3-hexyl-methilimidazolium tetrafluoroborate ([hmim][BF4]). It has been accomplished employing the composition of the mixtures (in terms of mole fraction) and the number of carbon atoms that form the lateral chain of the imidazolium cation as independent variables. All the utilized data was gathered from the literature and it corresponds to measurements that were carried out at 298.15 K. The mean prediction error for the estimation of this property was 6.42% and its R2 value 0.991. These results support that the application of nonlinear mathematical models which rely on ANNs can lead to an accurate estimation of ionic conductivity values of aqueous binary mixtures of imidazolium-based ionic liquids.

Direct Correlation Between the H/D Exchange Reaction and Conformational Changes of the Cation in Imidazolium-Based Ionic Liquid–D2O Mixtures

We present a study on the effects of deuterated water on the conformational equilibria of the imidazolium cation in aqueous mixtures of imidazolium-based ionic liquids at room temperature. We provide spectroscopic evidence that the conformational dynamics of the imidazolium cation in D2O are directly related to the H/D exchange reaction of the C–H group at position 2 on the imidazolium ring. The relation is supported by comparing Raman spectra obtained from solutions prepared with H2O and D2O.

Surface structures of binary mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy and time of flight secondary ion mass spectroscopy

Surface structures of binary mixtures of imidazolium-based ionic liquids having a common anion (bis(trifluoromethanesulfonyl)imide ([TFSI]), namely [C2MIM]1-x[C10MIM]x[TFSI] (x = 0.5 and 0.1), are studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and time of flight secondary ion mass spectroscopy (TOF-SIMS). Although both measurements show surface segregation of [C10MIM] the degrees of the segregation are different. The surface fraction xsurf of [C10MIM] is estimated to be 0.6 ± 0.05 and 0.18 ± 0.02 by HRBS for x = 0.5 and 0.1, respectively. On the other hand, TOF-SIMS indicates much stronger surface segregation, namely xsurf = 0.83 ± 0.03 and 0.42 ± 0.04 for x = 0.5 and 0.1, respectively. The observed discrepancy can be attributed to the difference in the probing depth between HRBS and TOF-SIMS. The observed surface segregation can be roughly explained in terms of surface tension.

Using Partial Least-Squares Regression in Multivariate UV Spectroscopic Analysis of Mixtures of Imidazolium-Based Ionic Liquids and 1-Methylimidazole for Measurements of Liquid–Liquid Equilibria

Recent interest in the use of room-temperature ionic liquids in various industrial applications sets requirements for analytical techniques that could lead to an efficient determination of concentrations of ionic liquids and/or possible impurities contained in them. Catalytic processes are particularly sensitive to the amount of impurities in the reaction media. Finding suitable and efficient techniques of determining compositions of liquid mixtures appears to be of importance not only for the design and optimization of such catalytic processes but also in measurements of phase equilibria. Imidazolium-based ionic liquids are often contaminated by their precursors 1-chlorobutane and 1-methylimidazole. Therefore, in this work a calibration technique is proposed that makes use of partial least-squares regression in UV spectroscopic determination of concentrations of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-methylimidazole. Spectra of these compounds show significant overlaps making their simultaneous quantitative analysis difficult. Partial least-squares regression using the PLS2 algorithm provides an effective resolution, decomposing complicated spectra and coping with component interferences, nonlinearities and collinearity. The calibration method for the chosen compounds was validated using test samples of known composition and by measuring liquid–liquid equilibria at 298.15 K in the ternary system 1-butyl-3-methylimidazolium hexafluorophosphate + 1-methylimidazole + 1-chlorobutane.