Melting Point Of Ionic Liquids Research Articles

Multichannel Conductivity Measurement Equipment for Efficient Thermal and Conductive Characterization of Nonaqueous Electrolytes and Ionic Liquids for Lithium Ion Batteries

Knowledge of the (specific) conductivities (κ) of nonaqueous electrolytes and their liquid range are key issues for the development and optimization of lithium ion batteries. Solidification and melting points of ionic liquids (ILs) cannot be determined easily, as ILs show a tendency toward supercooling, especially when high cooling rates are needed to get useful signals. Therefore, we have developed an integrated computer-controlled measurement apparatus that allows the determination of conductivity and solidification or fusion points as functions of temperature simultaneously for up to 30 samples and at very small cooling rates (as low as 1 K·h−1). The accuracy of the conductivity measurement equipment was analyzed by the error propagation law and by experiments as well. Over the range 5 μS·cm−1 to 5 mS·cm−1, relative uncertainties of better than 2 % of the measured values were achieved. The relative resolution of the conductivity measurements is better than 0.001 times the measured value. A detailed des...

Is the liquid or the solid phase responsible for the low melting points of ionic liquids? Alkyl-chain-length dependence of thermodynamic properties of [C nmim][Tf 2N

To establish the alkyl-chain-length dependences of thermodynamic properties of typical ionic liquids [C n mim][Tf 2N], the heat capacities of compounds with n = 2 and 18 were measured by adiabatic calorimetry. The comparison with other ionic liquids and typical molecular substances reveals that the low melting point of [C n mim][Tf 2N] with a short alkyl chain mainly originate in the large fusion entropy arising from the low entropy of the crystalline phase.

Group Contribution Method for Predicting Melting Points of Imidazolium and Benzimidazolium Ionic Liquids

A new model is proposed here to estimate melting points of imidazolium and benzimidazolium ionic liquids (ILs) from chemical structures by using a group contribution method, which considers the contributions of normal groups, ionic groups, and characteristic factors of molecules. The melting points of ILs are fitted by the equation presented in this study. Thirty simple groups and three characteristic factors were defined in the model based on the optimization of property values of 155 ionic liquids. The average relative deviation in this work is less than 5.86%, and calculated values of an additional 35 ILs are compared with the values in the literature. The R2 for 190 ILs is about 0.8984. The results show that melting points of ILs determined by the method are accurate and thus the new model can be applied to predict melting points of ILs.

Relative Hydrophobicity and Hydrophilicity of Some “Ionic Liquid” Anions Determined by the 1-Propanol Probing Methodology: A Differential Thermodynamic Approach

The excess partial molar enthalpy of 1-propanol (1P), H(E) (1P), was experimentally measured in ternary 1P-[NaPF(6), NaCF(3)SO(3) (OTF) or NaN(SO(2)CF(3))(2) (TFSI)]-H(2)O system. From the H(E) (1P), the enthalpic 1P-1P interaction function, H(E) (1P-1P), which is the compositional derivative of H(E) (1P), was evaluated graphically. On addition of the Na salt, the x(1P)-dependence pattern of H(E) (1P-1P) showed a characteristic change. This induced change is used as a probe to elucidate the effect of the sample Na-salt on H(2)O. Because we know the effect of Na(+) from our previous work, we show that each anion works as an amphiphile with hydrophobic and hydrophilic effects. Furthermore, the present method can quantify its relative hydrophobicity and hydrophilicity separately. The results indicate that the relative hydrophobicity ranking was in the order of TFSI(-) > PF(6-) approximately OTF(-), and the hydrophilicity TFSI(-) > PF6(- )> OTF-. Namely, TFSI- is the strongest amphiphile with the strongest hydrophobicity and the strongest hydrophilicity among the ionic liquid (IL) anions studied here. Using our earlier similar studies for normal ions, we map their relative hydrophobicity/hydrophilicity scales on a two-dimensional map together with those of the IL ions. The resulting map shows that the typical constituent ions for "ionic liquids" are strong amphiphiles; with more strongly hydrophobic and more strongly hydrophilic propensities than normal ions. Although the number of data points is limited, the melting points of ionic liquids consisting of TFSI(-) with the strongest hydrophobicity and the strongest hydrophilicity within the anions studied here are the lowest.

Optimising an artificial neural network for predicting the melting point of ionic liquids

We present an optimised artificial neural network (ANN) model for predicting the melting point of a group of 97 imidazolium salts with varied anions. Each cation and anion in the model is described using molecular descriptors. Our model has a mean prediction error of 1.30%, a regression coefficient of 0.99 and a mean P-value of 0.92. The ANN's prediction performance depends mainly on the anion size. In particular, the prediction error decreases as the anion size increases. The high statistical relevance makes this model a useful tool for predicting the melting points of imidazolium-based ionic liquids.

Anion and Cation Effects on Imidazolium Salt Melting Points: A Descriptor Modelling Study

The challenge of predicting the melting point of ionic liquids is outlined. A descriptor modelling approach for two separate sets of ionic liquids is presented. In each case, the cations and the anions are modelled separately, using quantitative structure-property relationships. Both models include constitutional, topological and geometric descriptors as well as quantum mechanical ones. This approach gives access to (nxm) ionic liquids using only (n+m) calculations. The protocol is tested and validated for predicting the melting points of two sets, comprised of 22 and 62 imidazolium-based ionic liquids, respectively. Good correlations and predictions are obtained in both cases. Within the data set selected (only monopositive and mononegative ions are studied, and so total charge was not a factor), the degree of sphericity is the most important variable for the anion, while for the cation the main descriptors pertained to three radial distribution functions that describe three different sections in the cation. These characterise the ionic interactions, the symmetry-breaking region, and the length of the side chains.

Prediction of the melting points for two kinds of room temperature ionic liquids

Melting points are significant properties for the design and application of ionic liquids (ILs) as green solvents. In this work, the melting points of two kinds of room temperature ionic liquids, imidazolium tetrafluoroborates and imidazolium hexafluorophosphates, were investigated by using a quantitative structure–property relationship (QSPR) approach. The employed descriptors were firstly selected by studying the optimized geometries of four ILs: EmimBF 4, BmimBF 4, EmimPF 6 and BmimPF 6. Electrostatic, quantum mechanical and topological descriptors were considered efficient to describe melting points of ionic liquids. A three-parameter model with the squared correlation coefficient, R 2, of 0.9047 is developed for 16 kinds of imidazolium tetrafluoroborates, and a six-parameter equation with R 2 of 0.9207 is obtained for 25 kinds of imidazolium hexafluorophosphates. The proposed models can be useful for the prediction of the melting points of ILs with similar structural features.

Solubility of Ionic Liquid [emim][PF6] in Alcohols

The solubility of 1-ethyl-3-methylimidazolium hexafluorophosphate, [emim][PF6], in alcohols (methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, tert-butyl alcohol, and 3-methylbutan-1-ol) has been measured by a dynamic method from 290 K to the melting point of ionic liquid or to the boiling point of the solvent. The solubility of [emim][PF6] in alcohols decreases with an increase of the molecular weight of the solvent and is higher in secondary alcohols than in primary alcohols. In every case, with the exception of methanol, the mutual liquid−liquid equilibrium was observed. The shape of the equilibrium curve is similar for [emim][PF6] in every alcohol. The observation of the upper critical solution temperature was limited by the boiling temperature of the solvent. The liquidus curves were correlated by means of two modified nonrandom two-liquid and the UNIQUAC ASM equations utilizing parameters derived from the solid−liquid equilibrium.

Ionic Liquids with Low Melting Points and Their Application to Double-Layer Capacitor Electrolytes

Ionic liquids, 1-ethyl-3-methylimidazolium hexafluorotantalate (EMITaF 6 ) and hexafluoroniobate (EMINbF 6 ) were synthesized by a new method. They showed lower melting points and higher decomposition temperatures than popular EMIBF 4 due to larger anion size. Electrolytic conductivities of these ionic liquids were about 6 mS cm - 1 at 25°C. Lowering the melting point of ionic liquids did not result in the improvement of low-temperature characteristics of carbon double-layer capacitors, however, the new ionic liquids showed long life compared with EMICF 3 SO 3 , EMI(CF 3 SO 2 ) 2 N, and EMI(C 2 F 5 SO 2 ) 2 N at 3.0 V, 70°C. The derivatives of the new ionic liquids having a methyl group in 2-position (l-ethyl-2,3-dimethylimidazolium salts) were not ionic liquids at room temperature.

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The melting points of ionic liquids (ILs) of imidazolium bromides and imidazolium chlorides have been investigated by means of quantitative structure–activity relationship (QSAR) approach in order to develop prediction models for predicting the melting points of ionic liquid salts. The cationic structures of these ILs were optimized by means of Hyperchem software and MOPAC program. QSAR module of Materials Studio software and Genetic Algorithm (GA) programs were employed to calculate and select the structure descriptors of ILs, then prediction models correlating the selected structure descriptors and melting points of ionic liquids were set up by using the multiple linear regressions (MLR) method and the back-propagation artificial neural network (BP ANN) method, separately. Finally, the obtained QSAR models, including MLR model and BP ANN model, were validated by external test sets. In this work, three data sets, which were 30 imidazolium bromides, 20 imidazolium chlorides and the merging of above two data sets, respectively, were used to investigate the QSAR correlation of the melting points of ILs. The results demonstrated that the prediction mean absolute errors (MAEs) of MLR models for test sets of those three data sets were in the order of 20.52 K, 13.59 K and 21.95 K, and the prediction MAEs of BP ANN models were 8.77 K, 4.98 K and 9.31 K, respectively. It indicated that the predictions of two models for all melting points of ILs were reliable, and the prediction precision of BP ANN model was higher than that of MLR model.