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Here, we report the results of qualitative and quantitative investigations of the first-order phase transition in the ionic liquid 1-ethylpyridinium triflate exhibiting a high variability of temperature ranges, within which the freezing and melting occur. By two methods, the direct fast quenching/annealing and the slow temperature-controlled differential scanning calorimeter, it is revealed that despite the almost constant absolute enthalpies of phase transition, the freezing occurs faster with the larger temperature contrast (cooling rate) between the initially hotter sample and the colder surrounding. This feature is a clear exhibition of the Mpemba effect. The regularity in the change of the melting point is analyzed as well. [ABSTRACT FROM AUTHOR]

In this work, we explore the possibility for calculating the isothermal compressibility of Ionic Liquids at atmospheric pressure by combination of the C at B oost machine learning library and Wada's rule. The C at B oost predicts the isothermal compressibility at 298.15 K using the density at the same temperature, the critical temperature and pressure, the molar mass, and the acentric factor. The obtained value plays the role of reference one combined with the power-law dependence on the density to get the target compressibility in a wider temperature range. The isothermal compressibilities for 35 Ionic Liquids, given in literature, were used for the comparison and its analysis. The average result at 298.15 K was 6.0% while for the whole range of temperatures was 6.2%. The influence of machine learning parameters on the prediction is discussed. • Combining numerical and categorical features for the prediction of isothermal compressibility coefficient. • Forecast's uncertainty quantification. • Quantitative analysis of quantities affecting the isothermal compressibility coefficient. [ABSTRACT FROM AUTHOR]

We report new experimental data of the ultrasonic measurements in three ionic liquids with triflate anion: 1-ethylpyridinium triflate, 1-butyl-3-methylimidazolium triflate, diethylmethylammonium triflate. The speed of sound was determined in the temperature range of (297 – 374) K and the pressure range of (0. 1 – 196. 2) MPa. In addition, the respective densities in this range were found using the acoustic route. For the first two substances, the effect of pressure-induced solidification is detected. It is shown that the high-pressure data on the sound velocity can be accurately predicted by applying the pressure fluctuation theory-based model using parameters, which requires only the data determined at the ambient atmospheric pressure. In turn, the density can be predicted using the Fluctuation Theory-based Equation of State (FT-EoS), which includes the isothermal nonlinearity parameter, which is argued as related to the frequency of interparticle oscillations. This interdependence is confirmed by the comparative analysis with the respective peak in the low-frequency Raman–Kerr spectrum. • The speed of sound is measured and the density is determined to 196. 1 MPa. • Pressure-induced freezing of ionic liquids at macroscopic volumes is detected. • Interplay of thermodynamics and microscopic interparticle oscillations is discussed. [ABSTRACT FROM AUTHOR]

This study reports synthesis of a new ionic liquid ethyl-1-octyloxymethylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2 imC 1 OC 8 ][NTf 2 ]) and its speed of sound data at 295.15 K ≤ T ≤ 373.15 K and 1 bar ≤ P ≤ 1471.5 bar. In addition, the atmospheric pressure densities of this IL were measured at 292.05 K ≤ T ≤ 423.65 K and determined at 295.15 K ≤ T ≤ 373.15 K and 1 bar ≤ P ≤ 1500 bar. Basing on a representative variety of ILs, it is demonstrated that the CP-PC-SAFT EOS adjusted to their high-pressure density data by a standardized numerical procedure and attached by a simple expression for estimating the ideal gas heat capacities is capable to predict sound velocities in a particularly accurate manner, with AAD around 1% and at times even smaller that the experimental uncertainties. • The new IL [C 2 imC 1 OC 8 ][NTf 2 ] was synthesized. • Its speeds of sound were measured in wide range of T and P conditions. • The parameters of CP-PC-EOS were fitted to the determined densities. • The predictions CP-PC-EOS deviate from the speeds of sound data by ~1%. [ABSTRACT FROM AUTHOR]