A Fluctuation Equation of State for Prediction of High-Pressure Densities of Ionic Liquids

Combining the Tait equation with the phonon theory allows predicting the density of liquids up to the Gigapascal range

Predicting the density of liquids at ultrahigh pressures in the case when only the data measured at ambient pressure are available is a long-standing challenge for thermodynamic research. In this work, we archived this goal for molecular liquids by applying the half-sum of the Tait equation and the Murnagnan equation in the form coordinated with Tait's at low pressure for predicting the density of molecular liquids up to the pressures more than 1 GPa with uncertainty comparable with the experimental one. It is shown that the control parameter, which is needed in addition to the initial density and the isothermal compressibility can be found using the speed of sound and the density at ambient pressure and has a clear physical interpretation in terms of the characteristic frequency of intermolecular oscillation mimicking the limiting frequency of Debye's theory of heat conductivity of solids. This fact is discussed as arguing in favour of the modern phonon theory of liquid thermodynamics and expands it range of applicability to the volumetric properties of liquids at temperatures far below the critical one. The validity of the model is illustrated with the case study of classic Bridgman's dataset as well as with some examples of ultrahigh-pressure data obtained by the diamond anvil cell and shock wave compression methods.

Industrial Applications of Ionic Liquids

Since their conception, ionic liquids (ILs) have been investigated for an extensive range of applications including in solvent chemistry, catalysis, and electrochemistry. This is due to their designation as designer solvents, whereby the physiochemical properties of an IL can be tuned for specific applications. This has led to significant research activity both by academia and industry from the 1990s, accelerating research in many fields and leading to the filing of numerous patents. However, while ILs have received great interest in the patent literature, only a limited number of processes are known to have been commercialised. This review aims to provide a perspective on the successful commercialisation of IL-based processes, to date, and the advantages and disadvantages associated with the use of ILs in industry.

The prediction of high-pressure volumetric properties of compressed liquids using the two states model

In this work, we argue that the volumetric properties of liquids cannot be reproduced by a single isothermal equation of state derived by the compressibility route for the whole pressure region extended up to a GPa pressure but require the consideration of two states associated with qualitatively different molecular packing properties. This is confirmed by examples of polar and non-polar substances within the range of temperatures from 203.15 K to 491.48 K and pressures up to 1200 MPa. The proposed two states model is truly predictive for the high-pressure density and isothermal compressibility using several easily measurable physico-chemical quantities: the density, the isobaric heat capacity, and the speed of sound at atmospheric pressure only. The experimental data on the density for 15 different compressed liquids, given in the literature as a function of temperature and very high-pressures, were used for the comparison and its analysis. The relative absolute average deviation for 2138 experimental data points by a two states model is close to 0.17%.

Density fluctuations and random walks in an overdamped and supercooled simple liquid

In this work, the short-time dynamics of simple liquid is explored both analytically and numerically with the focus on the interplay between the density fluctuations in a volume surrounding a chosen particle and its random walk motion. The particles interact via the Lennard-Jones potential with parameters corresponding to liquid argon. For large times, analytical calculations based on the fluctuation theory provides an explicit expression reproducing isothermal change of the self-diffusion coefficient in liquid argon corresponding to the experimental data. These results lead to the conclusion that such behavior is based on the reduced mobility of particles reflected in their density fluctuations that can be equivalently achieved in the cases of either low temperatures and pressures (supercooling) or moderate temperatures and high pressures (overdamping).