Viscosity Of Ionic Liquids Research Articles

Densities at Pressures up to 200 MPa and Atmospheric Pressure Viscosities of Ionic Liquids 1-Ethyl-3-methylimidazolium Methylphosphate, 1-Ethyl-3-methylimidazolium Diethylphosphate, 1-Butyl-3-methylimidazolium Acetate, and 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide

High pressure densities at (10–200) MPa over a range of temperatures and atmospheric pressure viscosities at (293–373) K for three ionic liquids (ILs) that are able to dissolve biomass, 1-ethyl-3-methylimidazolium methylphosphate ([emim][MP]), 1-ethyl-3-methylimidazolium diethylphosphate ([emim][DEP]), and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) are reported. Densities of the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) were measured at the same conditions to verify the apparatus and to extend the range of present data. The high pressure densities of [emim][MP] and [emim][DEP] are newly measured in this work. Combined expanded uncertainties of densities for [emim][MP], [emim][DEP], [bmim][Ac], and [bmim][Tf2N] were estimated to be 1.5 kg·m–3, 1.4 kg·m–3, 1.4 kg·m–3, and 1.7 kg·m–3, respectively. The Tait equation could correlate the experimental density data to within 0.03 % of average relative deviation. The derivative properties, isobaric expansivity, and isot...

Experimental investigation of natural convection heat transfer of Al2O3 Nanoparticle Enhanced Ionic Liquids (NEILs)

Experimental investigations were carried out regarding natural convection heat transfer of Nanoparticle Enhanced Ionic Liquids (NEILs) in rectangular enclosures of two different sizes with dimensions length×width×height, 50×50×50mm and 50×50×75mm in heated from below. The NEILs were synthesized by dispersing different wt% (0.5, 1.0, and 2.5) of aluminum oxide (Al2O3) nanoparticles of two different particle shapes (spherical and whiskers) into N-butyl-N-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl} imide, ([C4mpyrr][NTf2]) ionic liquid (IL). Heat transfer related thermophysical properties, i.e. density, viscosity, thermal conductivity, and heat capacity of base IL and NEILs were also measured and reported. The experimental measurement shows enhanced density, thermal conductivity, viscosity, and heat capacity of NEILs compared to the base IL and they increase with the nanoparticle concentration. However natural convection heat transfer coefficient was observed to deteriorate for the NEILs compared to the base IL irrespective of the shapes of the particles and aspect ratio of the enclosure and the deterioration increases with the increase of nanoparticle concentration. Interestingly spherical Al2O3 NEILs was observed to affect more adversely compared to the whiskers Al2O3 NEILs. The observed degradation of the heat transfer performance of the NEILs could not fully be explained by the change of thermophysical properties, which indicates that other factors may play significant roles in this phenomenon and the possible reasons of the degradation is discussed in this paper.

A quantitative prediction of the viscosity of ionic liquids using S(σ-profile) molecular descriptors.

In this study, two novel QSPR models have been developed to predict the viscosity of ionic liquids (ILs) using multiple linear regression (MLR) and support vector machine (SVM) algorithms based on Conductor-like Screening Model for Real Solvents (COSMO-RS) molecular descriptors (Sσ-profile). A total data set of 1502 experimental viscosity data points under a wide range of temperatures and pressures for 89 ILs, is employed to train and verify the models. The Average Absolute Relative Deviation (AARD) values of the total data set of the MLR and SVM are 10.68% and 6.58%, respectively. The results show that both the MLR and SVM models can predict the viscosity of ILs, and the performance of the nonlinear model developed using the SVM is superior to the linear model (MLR). Furthermore, the derived models also can throw some light onto structural characteristics that are related to the viscosity of ILs.

Combined effect of ether and siloxane substituents on imidazolium ionic liquids

The combined effect of ether and siloxane substituents on imidazolium cations helps overcome the Coulombic attraction, van der Waals forces, size factor and conformational degree of freedom, and exerts an impact on viscosity, density and thermal properties of ionic liquids.

The tricyanomethanide anion favors low viscosity of the pure ionic liquid and its aqueous mixtures.

Ionic liquids (ILs) constitute a broad research interest. One of the serious drawbacks of ILs is their high shear viscosity, which originates from bulky particles and strong cation-anion coordination. A continuous molecular design is being done to develop low-viscosity ILs. Low-viscosity ILs are also expected to exhibit an increased ionic conductivity. We investigate such an IL composed using a new anion (to the IL field) tricyanomethanide [C(CN)3](-) and the cation 1-ethyl-3-methylimidazolium [EMIM](+). Having developed the force field for [EMIM][C(CN)3], we simulate molecular dynamics (MD) of the pure IL and its mixtures with water over an entire range of compositions. According to MD simulations, [EMIM][C(CN)3] exhibits unusually low shear viscosity (for the imidazolium family) and high ionic conductivity. This is achieved thanks to weak cation-anion coordination and no hydrogen bonding between them. Furthermore, cation-water and anion-water hydrogen bonds were detected in the [EMIM][C(CN)3]/water mixtures. We correlate the structure and dynamics of [EMIM][C(CN)3] in aqueous mixtures to provide guidelines for future development of low-viscosity and highly conductive ILs.

Molecular features contributing to the lower viscosity of phosphonium ionic liquids compared to their ammonium analogues.

Molecular features contributing to the lower viscosity of phosphonium based ionic liquids (ILs) compared to ammonium based ILs are investigated by static quantum chemistry calculations and classical molecular dynamics simulations. The larger bond distance and the higher flexibility of bond angles and dihedral angles in the phosphonium compounds tend to reduce their viscosity compared to ammonium analogues, while the strongly localized charge at the central atom has the opposite effect. Fast translational ion dynamics is also found to be related to a short counter-ion association lifetime in the investigated compounds. Furthermore, a weak structuring between the center of charges also seems to increase mobility. Interestingly, the order of ion pair interaction energies in the gas phase is reversed compared to the order of counter-ion association lifetimes in the liquid, which highlights the important role of solvation in ILs. Overall, the higher flexibility of the bond and dihedral angles of the phosphonium compounds appears to be the most important factor in producing the lower viscosity of these ILs compared to their ammonium analogues.

Study on the temperature-dependent coupling among viscosity, conductivity and structural relaxation of ionic liquids.

The frequency-dependent viscosity and conductivity of three imidazolium-based ionic liquids were measured at several temperatures in the MHz region, and the results are compared with the intermediate scattering functions determined by neutron spin echo spectroscopy. The relaxations of both the conductivity and the viscosity agree with that of the intermediate scattering function at the ionic correlation when the relaxation time is short. As the relaxation time increases, the relaxations of the two transport properties deviate to lower frequencies than that of the ionic structure. The deviation begins at a shorter relaxation time for viscosity than for conductivity, which explains the fractional Walden rule between the zero-frequency values of the shear viscosity and the molar conductivity.

BODIPY-BODIPY dyad: assessing the potential as a viscometer for molecular and ionic liquids.

A symmetrical BODIPY-BODIPY dyad with a diyne linker was prepared in two steps; the lifetime decay of this rotor appeared to correlate with the viscosity of the media, thus making this dyad a suitable small molecule viscometer for molecular solvents. The potential of using the rotor to probe the viscosity of ionic liquids was also investigated.

Modeling the Viscosity of Ionic Liquids with the Electrolyte Perturbed-Chain Statistical Association Fluid Theory

In this work, the friction theory (FT) and free volume theory (FVT) were combined with the electrolyte perturbed-chain statistical association fluid theory (ePC-SAFT) in order to model the viscosity of pure ionic liquids (ILs) and IL/CO2 mixtures in a wide temperature and pressure (up to 3000 bar) range and with viscosities up to 4000 mPa·s. The ePC-SAFT pure-component parameters for the considered imidazolium-based ILs were adopted from our previous work. These parameters were used to calculate the density and residual pressure of the pure ILs. The density and pressure were then used as inputs for pure-IL viscosity modeling using FVT or FT, respectively. The viscosity-model parameters of FT and FVT were obtained by fitting to experimental viscosity data of imidazolium-based ILs and linearized with the molecular weight of the IL-cation. As a result, the FT viscosity model can more accurately describe the experimental viscosity data of pure ILs than the FVT model, at the cost of an increased number of para...

Applicability of different equations in modeling the thermodynamic and transport properties of aqueous and non-aqueous ionic liquid solutions

Applicability of different electrolyte based models has been tested in correlating the osmotic coefficient values of aqueous and nonaqueous binary ionic liquid solutions considering both the complete and partial dissociation of the ionic liquids. In local composition models the sum of a long-range and a short-range term is used. When the partial dissociation of ionic liquid is considered, the Pitzer–Debye–Hückel and Fowler–Guggenheim equations were used to calculate the long-range electrostatic interaction. In the Fowler–Guggenheim equation, for calculating Debye inverse length the necessary degree of association has been determined from osmotic coefficient data by Chemical Model (CM1). The correlation equations for excess molar volume of the NRTL–NRF, mNRTL, NRF–Wilson and NRF–mNRTL models for ionic liquid or electrolyte solutions were also derived. The performance of these equations was compared with the other available models for correlating the excess molar volume of ionic liquid solutions. Taking into account of complete or partial dissociation of ionic liquids, fitting quality of solution viscosities of various ionic liquids were examined using the Eyring’s absolute rate theory and different electrolyte local composition models and Clegg–Pitzer equations.

Estimation of the Viscosity of Ionic Liquids Containing Binary Mixtures Based on the Eyring’s Theory and a Modified Gibbs Energy Model

Eyring’s absolute rate theory was applied for evaluation of the viscosity of ionic liquids (ILs) containing binary mixtures. Considering the mathematical simplicity of the two-suffix-margules model, the Gibbs energy model was further modified. Furthermore, for viscosity evaluation, the proposed Gibbs energy model was coupled with Eyring’s theory. To validate the accuracy of the proposed model, a large set of data containing the binary mixtures of 122 ILs with a total number of 5512 experimental data points was collected from the literature. Moreover, the average absolute relative deviation (AARD %) was obtained as 2.07 %. Also, the capability of the Eyring–MTSM model was tested for the prediction of viscosity for binary and ternary systems. Additionally, comparison of the proposed model with the Eyring–NRTL model indicated a higher accuracy for our model. Finally, the Eyring–UNIFAC model was also checked, and it was found that this model is not accurate enough in its present form.

Density, Viscosity and Surface Tension of Binary Mixtures of 1-Butyl-1-Methylpyrrolidinium Tricyanomethanide with Benzothiophene.

The effects of temperature and composition on the density and viscosity of pure benzothiophene and ionic liquid (IL), and those of the binary mixtures containing the IL 1-butyl-1-methylpyrrolidynium tricyanomethanide ([BMPYR][TCM] + benzothiophene), are reported at six temperatures (308.15, 318.15, 328.15, 338.15, 348.15 and 358.15) K and ambient pressure. The temperature dependences of the density and viscosity were represented by an empirical second-order polynomial and by the Vogel–Fucher–Tammann equation, respectively. The density and viscosity variations with compositions were described by polynomials. Excess molar volumes and viscosity deviations were calculated and correlated by Redlich–Kister polynomial expansions. The surface tensions of benzothiophene, pure IL and binary mixtures of ([BMPYR][TCM] + benzothiophene) were measured at atmospheric pressure at four temperatures (308.15, 318.15, 328.15 and 338.15) K. The surface tension deviations were calculated and correlated by a Redlich–Kister polynomial expansion. The temperature dependence of the interfacial tension was used to evaluate the surface entropy, the surface enthalpy, the critical temperature, the surface energy and the parachor for pure IL. These measurements have been provided to complete information of the influence of temperature and composition on physicochemical properties for the selected IL, which was chosen as a possible new entrainer in the separation of sulfur compounds from fuels. A qualitative analysis on these quantities in terms of molecular interactions is reported. The obtained results indicate that IL interactions with benzothiophene are strongly dependent on packing effects and hydrogen bonding of this IL with the polar solvent.Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-014-0257-1) contains supplementary material, which is available to authorized users.

Predicting the viscosity and electrical conductivity of ionic liquids on the basis of theoretically calculated ionic volumes

Selected physical properties of the ionic liquids might be quantitatively predicted based on the volumes of the ions these systems are composed of. It is demonstrated that the ionic volumes calculated using relatively simple theoretical quantum chemistry methods can be utilised to estimate the viscosities and electrical conductivities of various commonly used ionic liquids. The fitting formulas of the exponential form are offered and their predictive usefulness is verified. The quality of such predictions is discussed on the basis of several ionic liquids involving [Tf2N]‑ and [BF4]‑ anions and 16 various cations. The dependence of the viscosity and electrical conductivity of the ionic liquids on the temperature is also investigated and the temperature-dependent equations are derived and compared to the experimentally measured values.

Nanosilica Supported Dual Acidic Ionic Liquid as a Recyclable Catalyst for the Rapid and Green Synthesis of Polycyclic Phenolic Compounds

Generally ionic liquids have gained increasing attention in organic synthesis as catalyst and solvent. However, there are some drawbacks, including the difficulties in the product purification, ionic liquid recycling, and use of excess amounts of the expensive ionic liquid when the ionic liquid is used in the organic reactions. In addition, the high viscosity of ionic liquids can lead to mass transfer limitations in fast chemical reactions. These problems can be overcome by the use of supported ionic liquid phases. In this article, a simple, efficient and green method has been developed for the synthesis of bisphenolic antioxidants by the reaction of 2-tert-butyl-4-methylphenol and aldehydes in the presence of nanosilica supported dual acidic ionic liquid (NSSDAIL) as robust and reusable catalyst under solvent-free conditions. Three different NSSDAILs were synthesized and characterized using SEM, BET, IR, and XRD techniques. High yields of the products, short reaction times, use of a non corrosive, non toxic and reusable catalyst, and use of solvent-free condition are the worthwhile advantages of the current method.

Prediction of Density, Surface Tension, and Viscosity of Quaternary Ammonium-Based Ionic Liquids ([N222(n)]Tf2N) by Means of Artificial Intelligence Techniques

In this work, thermophysical properties of quaternary ammonium-based ionic liquids (ILs) including density, surface tension, and viscosity are produced by two powerful artificial intelligence techniques: genetic function approximation (GFA) and artificial neural network (ANN). In proposed GFA and ANN models, the critical temperature and water content of studied ILs ([N222(n)]Tf2N with n = 5, 6, 8, 10, and 12) as well as operation temperature were given as the input parameters and the density, surface tension, and viscosity were predicted as the output results. The obtained results reveal that the selected input parameters are appropriate for prediction of thermophysical properties of quaternary ammonium-based ILs. In addition, the high statistical quality represented by various criteria and the low prediction errors of the presented models indicate that they can accurately predict the density, surface tension, and viscosity of new ILs without recourse to experimental data.

Silylated quaternary ammonium salts – ionic liquids with hydrophobic cations

Another class of ionic liquids was obtained by a combination of bis(perfluoroalkylsulfonyl)amide anions and O-silylated choline like cations. The protection of the hydrophilic hydroxyl group of hydroxyalkyl substituted quaternary ammonium salts with a trialkylsilyl group changes cations' properties from hydrophilic to hydrophobic; both constituents (cations and anions) of resulting ionic liquids have a hydrophobic character. Their essential physical and chemical properties were investigated. Moderate viscosity and conductivity of ionic liquids follow the Vogel-Tammann-Fulcher model of their dependency on the temperature. All ionic liquids show similar electrochemical stability as anticipated from CV measurements. The cathodic stability for most compounds is below 0 V vs. Li/Li+, and anodic decomposition starts typically over more than 5 V vs. Li/Li+. These properties suggest that these ionic liquids have potential for the preparation of electrolytes for high voltage lithium batteries.

Engineering the electrochemical capacitive properties of graphene sheets in ionic-liquid electrolytes by correct selection of anions.

Graphene sheet (GS)-ionic liquid (IL) supercapacitors are receiving intense interest because their specific energy density far exceeds that of GS-aqueous electrolytes supercapacitors. The electrochemical properties of ILs mainly depend on their diverse ions, especially anions. Therefore, identifying suitable IL electrolytes for GSs is currently one of the most important tasks. The electrochemical behavior of GSs in a series of ILs composed of 1-ethyl-3-methylimidazolium cation (EMIM(+)) with different anions is systematically studied. Combined with the formula derivation and building models, it is shown that the viscosity, ion size, and molecular weight of ILs affect the electrical conductivity of ILs, and thus, determine the electrochemical performances of GSs. Because the EMIM-dicyanamide IL has the lowest viscosity, ion size, and molecular weight, GSs in it exhibit the highest specific capacitance, smallest resistance, and best rate capability. In addition, because the tetrafluoroborate anion (BF4(-)) has the best electrochemical stability, the GS-[EMIM][BF4] supercapacitor has the widest potential window, and thus, displays the largest energy density. These results may provide valuable information for selecting appropriate ILs and designing high-performance GS-IL supercapacitors to meet different needs.

Ionic liquid effects on mass transfer efficiency in extractive distillation of water–ethanol mixtures

The relatively high viscosities of ionic liquids could reduce the mass transfer efficiency of the extractive distillation process. The rate-based model was adopted to analyze this phenomenon since it predicted the performance of an extractive distillation pilot plant using ionic liquids as solvent. For the water–ethanol separation, three ionic liquids: 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium dicyanamide and the organic solvent ethylene glycol were used for the analysis. Simulations were conducted for sieve trays and Mellapak® 250Y. The results indicate that relatively high viscosities affect the mass transfer efficiency. However, the improvements in relative volatilities obtained from the ionic liquids help to overcome this effect. However, with high solvent viscosities (>65mPas at T=353.15K) it was not possible to overcome the reductions. Additionally, at higher distillate rates high relative volatilities yielded negative effects on mass transfer efficiency because of a decrease in vapor velocity.

Thermal performance of ionic liquids for solar thermal applications

Experimental investigations were carried out to evaluate thermophysical properties, i.e. density, viscosity, heat capacity, and thermal conductivity and high temperature forced convection behavior of N-butyl-N,N,N-trimetylammoniumbis(trifluormethylsulfonyl)imide ([N4111][NTf2]) ionic liquid (IL) for its potential application in concentrated solar power (CSP). Results from the experiments will be useful in assessing the potential of using ILs for solar thermal collectors. Experimental results show that thethermal conductivity was slightly decrease with the increase of temperature; vary from 0.124 to 0.121W/mK for a change in temperature of 283–343K, strong temperature effect on the viscosity of IL was observed and maintain an exponential relationship with the temperature; heat capacity increases linearly with temperature measured from 298 to 618K. Forced convection performance of the IL was studied in a circular tube under both in laminar and turbulent conditions. Although the heat transfer coefficient of the IL was found to be lower compared to the De-Ionized (DI) water, its thermal stability and other attractive properties may make it a viable candidate for solar collector use. Our experimental results also established that Shah’s equation and Gnielinski’s equation can predict forced convection performance of IL for both the laminar region and turbulent region respectively.

ChemInform Abstract: Ultrafast Solvation Dynamics and Charge Transfer Reactions in Room Temperature Ionic Liquids

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