Isobaric Thermal Expansion Research Articles

Thermodynamic and Transport Properties of Biomass-Derived Furfural, Furfuryl Alcohol and Their Mixtures

The limited reserves and well-known disadvantages of using fossil energy sources have increased the need for appropriate renewable substitutes in the production of various chemicals and materials. Biomass has been shown to be worthy of attention since it can be converted to biofuels and value-added chemicals relatively easily. The design of biomass valorisation process requires knowledge on the thermodynamic behaviour of the biomass-derived compounds, such as furfural and furfuryl alcohol. The thermodynamic and transport properties of the binary system furfural + furfuryl alcohol were studied at various temperatures and pressures. Density, speed of sound and refractive index were measured in the temperature range T = (288.15–345.15) K and viscosity was measured at temperatures up to 373.15 K, all at atmospheric pressure. Further, the density of pure components was obtained in the temperature range (293.15–413.15) K for furfural and (293.15–373.15) K for furfuryl alcohol at pressures up to 60.0 MPa. The obtained density values were correlated using the modified Tammann–Tait equation with an average absolute deviation lower than 0.009% for furfural and furfuryl alcohol. The optimised parameters were used for the calculation of the isothermal compressibility, the isobaric thermal expansivity, the internal pressure and the isobaric and isochoric specific heat capacities. The reported data are a valuable source of information for the further application of the investigated compounds.

Computation of Isobaric Thermal Expansivity from Liquid Density Measurements. Application to Toluene

Computation of Isobaric Thermal Expansivity from Liquid Density Measurements. Application to Toluene

More Accurate Determination of Isothermal Compressibility and Isobaric Thermal Expansivity Using Volume-Translated Equations of State

Isothermal compressibility, κT, and isobaric thermal expansivity, αP, can describe the volumetric behavior of a given fluid in response to the change in pressure and temperature, respectively. They are two important parameters that are used in the simulation and modeling of many petroleum and chemical processes. Isothermal compressibility and isobaric thermal expansivity can be calculated with empirical correlations or thermodynamic models, but these methods are not sufficiently accurate. Cubic equations of state (CEOSs) are widely used in the petroleum and chemical industry to describe the phase behavior of fluid mixtures. It is recognized that one of the deficiencies of CEOSs is their inaccuracy in predicting liquid-phase volumes. The volume translation (VT) strategy was proposed to overcome this deficiency, which could significantly improve the performance of CEOSs in predicting volumetric properties. With recent development in the volume-translated equations of state (VT-EOSs), κT and αP could be predicted more accurately by VT-EOSs. However, the prediction accuracy of κT and αP by different VT-EOSs has not been comprehensively investigated. In this work, κT and αP of two pure example fluids (CH4 and CO2) are predicted by seven different VT models: one constant VT model, two linear temperature-dependent VT models, two exponential temperature-dependent VT models, and two temperature-pressure-dependent VT models. The accuracy of each model is evaluated by comparing the predictions with the NIST pseudo-experimental data for the liquid phase, the vapor phase, and the supercritical phase. The predicted results show that the distance-function-based temperature-pressure-dependent VT models exhibit relatively better performance in predicting κT and αP than the temperature-dependent and the constant VT models. This is because the distance function is a function of both temperature and pressure, which allows the distance-function-based VTs to provide more accurate volume corrections for most of the phase regions and thus can lead to better accuracy in predicting κT and αP. According to the overall prediction accuracy, the VT-PR EOS model proposed by Abudour et al. (2012) provides the most accurate predictions of κT, while the VT-SRK EOS model proposed by Chen and Li (2020) provides the most accurate predictions of αP. The findings of this study can help to predict κT and αP of pure substances at different temperature and pressure conditions by using the most accurate VT-EOS and provide insights for further improvement of volume translation strategies.

Density and derived properties of standard seawater up to high pressure in stable and metastable states

In this work, a consolidated experimental apparatus for measuring the density of liquids, such as high pressure and metastable states, based on the isochoric method, was exploited to measure thermal properties of seawater. Density of standard seawater was measured in a wide range of temperature and pressure, specifically from (261.15 to 313.15) K and up to 110 MPa. All terms contributing to the uncertainty in determining the volume and the mass of the specimen were evaluated, obtaining a relative expanded uncertainty of seawater density around 0.03% (k=2). Experimental results were fitted by using a 8-parameters function of specific volume as a function of temperature and pressure. Using the obtained expression, density, isobaric thermal expansion, and isothermal compressibility of seawater were calculated from (263.15 to 313.15) K and for pressures between (1 and 105) MPa. A comparison with the predictions obtained by the Thermodynamic Equation of Seawater - 2010 (TEOS-10) shows a general good agreement that worsens when metastable states are considered.

A numerical study of supercritical carbon dioxide as a medium for thermal energy storage applications under natural convection

This numerical study investigates supercritical carbon dioxide (s-CO2) as a medium for thermal energy storage (TES) systems operating under natural convection regarding heat transfer coefficient and energy density. The numerical domain comprises a horizontal heated cylinder surrounded by the supercritical fluid. The modeling employs a 2-D formulation due to the axial symmetry while the constitutive equations consider that the thermophysical properties vary spatially with temperature and pressure. The results revealed thermodynamic states that maximize the heat transfer coefficient and energy density for constant-pressure operation. Besides, considering the numerous studies on correlations for the natural convection heat transfer coefficient for s-CO2, the analysis compares simulation data with correlations based on constant and integrated-averaged fluid properties. The results suggested that the constant-property formulation fails in the thermodynamic region where properties change significantly. Thus, this work proposes a criterion for deciding when to consider integrated-averaged properties regarding the behavior of the isobaric thermal expansion coefficient. Finally, the study extended the analysis to air, helium, and nitrogen while employing operational conditions suitable for power cycles using such fluids. The comparisons revealed that, among these competitors, helium presents the highest heat transfer coefficient, but s-CO2 has the highest energy density.

A new methodology for determining the temperature of maximum density against pressure. Application to 2-propanol and ethanol aqueous solutions

Aqueous solutions of 2-propanol and ethanol are experimentally studied in order to obtain the location of the maximum of density versus temperature at high pressure. To this aim, a new technique based on measuring the pressure against temperature for several quasi-isochores was developed. These data are combined with isothermal compressibility, experimentally obtained from high pressure density data, to determine the isobaric thermal expansivity in the quasi-isochores. The temperature of maximum density is obtained by detecting the temperature for which this magnitude becomes zero. These results are compared with those obtained using highly precise densitometry at atmospheric pressure and also with literature data. The differences between the temperature of maximum density for solutions and that of water are positive for very diluted solutions, but they become negative as concentration is raised, which constitutes a quite unusual behavior as compared with other systems. As pressure is raised, this anomalous behavior becomes much more pronounced with positive deviations that exceed 1.5 K at the highest pressures. The underlying microscopic picture that could explain the observed behavior is suggested.

Studies of solute - solvent interaction of ethyl acetate with 1-Butyl-3-methylimidazolium tetrafluoroborate at T = (298.15–323.15) K

In this work, densities and speeds of sound of binary mixtures of 1- butyl −3-methylimidazolium Tetrafluroborate ionic liquid (IL) with Ethyl acetate (EtOAc) have been measured at temperatures 298.15 – 323.15 K at atmospheric pressure. With the help of experimental results, a discussion is carried out on the molecular interactions and the effect of temperature on interactions through excess properties such as excess molar volumes, VmE, excess isentropic compressibility, κsE, excess speeds of sound, uE, excess molar isentropic compressibility, Ks,mE, excess isobaric thermal expansion,αpE. The excess properties are adequately fitted with the Redlich-Kister polynomial equation. The excess partial molar volumes, V¯m,1E and V¯m,2E; excess partial molar isentropic compressibilities, K¯s,m,1E and K¯s,m,2E; excess partial molar volumes, V¯m,1°E and V¯m,2°E; excess partial molar isentropic compressibilities, K¯s,m,1°E and K¯s,m,2°E of the components at infinite dilution also been measured.

Effects of 2-Butanol Addition on Waste Cooking Oil Biodiesel Density: An Updated Experimental Measurement and Thermodynamic Modeling Study

Biodiesels will become the most popular alternative energy resource to fossil diesels; they can be used alone or blended with an oxygenated additive in any proportion. The properties of biodiesels strongly depend on the type of the fatty acid methyl esters (FAME) that compose them. The main objective of the present work is to investigate the influence of 2-butanol addition on the waste cooking oil biodiesel (WCOB), for this fact, the new experimental density data (952 points) of WCOB + 2-butanol binary mixtures over a wide range of composition [seven compositions; 0 ≤ (WCOB) mole fraction x ≤ 1] between 0.1 and 140 MPa and 298.15 and 393.15 K are presented. The experimental data were correlated using Tait and perturbed chain-statistical associating fluid theory (PC-SAFT) equations of state (EoS), to our knowledge, this is the first time that density measurements for the WCOB + 2-butanol mixture are correlated using the famous PC-SAFT EoS. The Tait equation predicts successfully the density with a global absolute average deviation (AAD) of 0.089%, while the PC-SAFT model correlates well the density with a very small global AAD of 0.223% in each composition. Furthermore, contrary to the Tait equation, the PC-SAFT model can explain some interactions between fluid molecules. From the experimental data, the excess volumes VE have been calculated and fitted using the Redlich-Kister equation with a very small global standard deviation of 7.49 × 10-5 cm3 mol-1, and VE show a positive and symmetric parabolic shape in all composition ranges. Finally, the isobaric thermal expansivity, αp, and the isothermal compressibility, κT, have been derived from the Tait equation and their observed trend was as expected.

High pressure densities and derived thermodynamic properties of deep eutectic solvents with menthol and saturated fatty acids

Densities of four Deep Eutectic Solvents (DESs) based on menthol and organic acids (menthol:octanoic acid (1:1), menthol:decanoic acid (1:1), menthol:dodecanoic acid (2:1) and decanoic acid:octanoic acid (1:3)) were measured at high pressures (0.1 to 60) MPa and several temperatures (293.15 to 413.15) K. Tammann-Tait equation was used to model the experimental density data; the average absolute percentage deviations between calculated and experimental data were less or equal 0.012 %. The influence of the temperature and pressure on the derived volumetric properties: isothermal compressibility (kT), isobaric thermal expansivity (αp), internal pressure (pint) and difference between heat capacity at constant pressure (cp) and constant volume (cv) was analysed. Considering the experimental results, it is possible to observe that deep eutectic solvent formed by linear organic acids presents higher density values than those formed by menthol, being the densest the solvent formed by dodecanoic and octanoic acid. Attending to the derived volumetric properties in general, isothermal compressibility and isobaric thermal expansivity increase as temperature increases and decrease with pressure for all studied systems, being the octanoic acid based DESs slightly more compressible than the other studied DESs.

Liquid phase PVTx properties of {water (1) + 1,3-dimethylurea (2)} mixtures at temperatures from 278.15 to 323.15 K and pressures to 100 MPa

In this study, the compression coefficients k=ΔV/Vo of the binary mixture {water (1) + 1,3-dimethylurea (2)} were measured within the temperature range from 278.15 K to 323.15 K (278.15, 288.15, 288.15, 308.15, 323.15), the pressure range from 10 to 100 MPa (10, 25, 50, 75 and 100) and the composition range up to x2 = 0.19364 (1,3-dimethylurea mole fraction). The molar isothermal compression, KT,m, molar isobaric thermal expansion, EP,m, isochoric coefficient of thermal pressure, βV, and the internal pressure of the mixture, Pint, were calculated. It was demonstrated that the concentration dependences (on the mole fraction of 1,3-dimethylurea (1,3-DMU)) of the molar isothermal compressions of the mixture at low pressures and low temperatures are characterized by a minimum at x2≈0.06 ÷ 0.07, which levels out both with increase in pressure and with increase in temperature. The molar isobaric thermal expansion of the mixture increases with an increase in the 1,3-DMU concentration for all state parameters. At low temperatures, the concentration dependences of the molar expansion are characterized by the presence of a pressure inversion zone. The concentration dependences of the isochoric coefficient of thermal pressure of the mixture indicate the hydrophobic properties of the 1,3-DMU molecule become stronger at high pressures. The obtained results are discussed in terms of solute–solvent and solute–solute interactions.

The density, viscosity, speed of sound, excess properties of binary mixtures of linear polydimethylsiloxane and various alkanes at temperatures in the range (288.15–328.15) K

This article describes the binary system composed of linear polydimethylsiloxane (PDMS) and diesel fuel main components n-decane, n-dodecane, n-tridecane and n-tetradecane at atmospheric pressure, and the density, viscosity and speed of sound were measured at 288.15 K, 298.15 K, 308.15 K, 318.15 K and 328.15 K, respectively. Their excess molar volume (VmE), excess viscosity (ηE), excess molar Gibbs free energy (ΔGEm), molar isobaric thermal expansion (EP,m) and excess molar isentropic compressibility (κEs,m) were calculated. The influence of the intermolecular force, steric hindrance, molecular stacking and other factors on the excessive properties of the binary system solution was discussed. The results indicate that with an increase in carbon chain length, the excess molar volume, excess viscosity, molar isobaric thermal expansion and excess molar isentropic compressibility increased and excess molar Gibbs free energy decreased, which probably ascribe to the increase in steric effect and the stronger interactions between homo-molecular than those of hetero-molecular interactions between PDMS and long-chain alkane molecules.

Development of a robust soft-SAFT model for protic ionic liquids using new high-pressure density data

New experimental density data in a wide range of temperatures (283–363) K and pressures (0.1–95) MPa is here reported for five protic ILs based on the N,N-diethylethanolammonium ([DEEA]) cation, combined with the following anions: acetate ([Ace]), propanoate ([Prop]), butanoate ([But]), pentanoate ([Pent]) and hexanoate ([Hex]) in a 1:1 acid:base proportion. The molar volumes of the different ILs and derivative properties such as the isothermal compressibility and isobaric thermal expansivity were determined from the experimental density data. Moreover, considering the importance of having a robust and transferable thermodynamic model of these ILs that can be used in further studies including CO2 capture, the new experimental data was used to develop a coarse-grain molecular model of the studied ILs, in the framework of the soft-SAFT EoS, employing a 2/2 association scheme to account for the hydrogen bonding character of the ILs. The proposed model was found to provide an excellent description of the experimental pρT data with average relative deviations lower than 0.11% for all the ILs, while still providing reasonable predictions of the second-order derivative properties. Furthermore, the optimized molecular parameters were found to be correlated with the ILs molecular weight, highlighting the physical meaning and consistency of the parameters obtained.

PρT parameterization of SAFT equation of state: developing a new parameterization method for equations of state

The lack of a transparent and universal parameterization method is one of the main problems in developing SAFT-type equations of state and it's an obstacle in their way of becoming an industrial equation of state. Usually, vapor-pressure and saturated liquid density data with a local optimization algorithm are used to parameterize SAFT-type equations of state. In addition to the ambiguity in the data selection process, using a local optimization method reduces the accuracy of the estimated parameters. Therefore, in this paper, a new method for calculating the adjustable parameters of SAFT or any equations of state with several parameters is presented. By providing a clear and explicit data selection procedure, including data categorization, comparison, and validation, integrated with the use of a combination of global and local optimization methods, the new methodology achieves the best possible parameters set for the equation of state. The proposed computational program for fitting parameters is based on the use of the Differential evolution algorithm as the main process and the Levenberg-Marquardt algorithm as the post-process along with applying one (or two) hyperparameter. Afterward, a wide range of pressure-temperature-density data has been used to estimate the parameters of 60 non-associating and associating pure compounds. Then, the SAFT equation of state with the new parameters, so-called PρT-SAFT-HR, is applied to predict pressure (P), temperature (T), density (ρ), vapor-pressure (Psat), saturated vapor density (ρvapsat), saturated liquid density (ρliqsat), critical point, isochoric heat capacity (cv), isobaric heat capacity (cP), speed of sound (u), isothermal compressibility (κT), and isobaric thermal expansivity (αP). All properties are calculated with the PρT-SAFT-HR equation of state, and the results are compared with experimental data and SAFT-HR and the average absolute percentage deviation is reported for all of them. In total, 19460 experimental and pseudo-experimental data were used to reparameterization the SAFT equation of state, and more than 74,000 data were validated to calculate thermodynamic properties. The results showed a significant improvement in predicting second-order thermodynamic derivative properties. In general, PρT-SAFT-HR performs better than SAFT-HR, and in some cases, such as pressure, speed of sound, isothermal compressibility, and isobaric thermal expansivity, the results have been significantly improved, and the average absolute deviation of PρT-SAFT-HR has been much less than SAFT-HR.

Viscosity, density, and derived thermodynamic properties of aqueous 2-(ethylamino)ethanol (EAE), aqueous aminoethylethanolamine (AEEA), and its mixture for post-combustion CO2 capture

In the present study, viscosity and density of aqueous 2-(ethylamino)ethanol (EAE), aqueous aminoethylethanolamine (AEEA), and aqueous EAE + AEEA blend were measured in the temperature range of 293.15 K to 333.15 K at atmospheric pressure. Concentration of aqueous amines was used upto 30 wt% that is usually applicable for CO2 absorption from flue gases in post combustion CO2 capture process. EAE/AEEA weight ratio was 9/1, 8/2, and 7/3 in the aqueous EAE + AEEA blend. Viscosity of all mixtures increased by increasing amine concentration and decreased by increasing temperature of samples. Experimental viscosity data were correlated to newly proposed models and average absolute deviation (AAD) % was 1.515, 2.027, and 2.889 for viscosity of EAE + H2O, AEEA + H2O, and EAE + AEEA + H2O, respectively. Density of aqueous EAE and aqueous EAE + AEEA blend (at fixed EAE/AEEA weight ratio) decreased by increasing amount of amine in the mixture but aqueous AEEA showed increased density by increasing concentration of AEEA. Excess molar volume (VE) calculated for all aqueous mixtures and VE of aqueous EAE and aqueous AEEA was fitted in Redlich-Kister equation. Density of aqueous EAE + AEEA blend was correlated to a new empirical model and AAD % for this model was 0.018. Isobaric thermal expansion coefficient (αp) of binary and ternary solutions was calculated from density versus temperature data. Activation molar enthalpy (∆H∗), activation molar entropy (∆S∗), and activation molar Gibbs free energy (∆G∗) at 298.15 K for aqueous EAE, aqueous AEEA, and aqueous EAE + AEEA blend were calculated using viscosity and density data on the basis of Eyring theory of liquid viscosity.

Influences of composition and temperature on the behaviors of a binary mixture containing methanol and 1-ethylimidazole

As a further investigation on the binary mixtures containing 1-alkylimidazole, over the whole composition range and at atmospheric pressure, density, ρ, sound velocity, u, of binary system of x 1-ethylimidazole (abbreviated as 1-Eim) + (1-x) methanol, were measured at temperatures (293.15–328.15) K; refractive index, nD, and viscosity, η, of them were determined at temperatures (293.15–318.15) K; 1H NMR, δH, is measured at 288.15 K; isobaric thermal expansivity, αp, isentropic compressibility, κS, excess and deviation properties were calculated. The excess enthalpy and Gibbs free energy were predicted by COSMO-RS model.All the properties indicate that the real mixing process is a spontaneous enthalpy-driving process with liquid structure more ordered, and a lower temperature more benefits the process. There are stronger attractive interactions in the mixture than in pure liquids. The H-bonded interactions are the main attractive interactions in the mixture, followed by the electrostatic/misfit interaction and the Van der Waals force. A H-bonded network with a ration of methanol:1-Eim = 1:1 appears in the mixture, and reaches its maximum amount at x about 0.4; via the N···HO, the rearrangement of electron densities occurs where protons of 1-Eim and hydroxyl all show electron-donating abilities while methyl protons of methanol show electron-withdrawing ability.

Molecular Interaction Studies of Doxycycline Hyclate in Aqueous Glycine or l-Alanine by Using Volumetric and Ultrasonic Parameters

The intermolecular interactions of the antibiotic drug doxycycline hyclate in water, aqueous solutions of glycine and aqueous solutions of l-alanine were determined by using volumetric and acoustic methods at four different temperatures (305.15, 310.15, 315.15 and 320.15) K. The limiting partial molar volume $$(V_{\phi }^{{\text{o}}} )$$ , limiting standard partial molar volume of transfer $${(}\Delta_{{{\text{tr}}}} V_{\phi }^{{\text{o}}} )$$ , limiting partial molar adiabatic compressibility ( $$\kappa_{\phi ,s}^{{\text{o}}} )$$ and limiting partial molar adiabatic compressibility of transfer $${(}\Delta_{{{\text{tr}}}} \kappa_{\phi ,s}^{{\text{o}}} )$$ were calculated from the density and ultrasonic velocity data at different temperatures and the results suggest strong solute–solvent interactions. The caging effect of doxycycline hyclate in water and in aqueous solutions of glycine and aqueous solutions of l-alanine was studied using the positive values of $$\left( {E_{\phi }^{{\text{o}}} = \frac{{{\updelta }V_{\phi }^{{\text{o}}} }}{{{\updelta }T}}} \right)$$ . The structure making behavior of doxycycline hyclate in water, aqueous solutions of glycine and aqueous solutions of l-alanine was analyzed from the positive values of Hepler’s constant i.e. $$\left( {\frac{{{\updelta }^{2} V_{\phi }^{{\text{o}}} }}{{{\updelta }T^{2} }}} \right)$$ . The limiting isobaric thermal expansion coefficient $$\left( {\alpha^{{\text{o}}} { } = \frac{{E_{\phi }^{{\text{o}}} }}{{V_{\phi }^{{\text{o}}} }}} \right)$$ , intermolecular free length (Lf) and acoustic impedance (Z) of doxycycline hyclate in water, aqueous solutions of glycine and aqueous solutions of l-alanine were also calculated at the studied temperatures.

Hydrophobic eutectic solvents: Thermophysical study and application in removal of pharmaceutical products from water

Exposure to persistent contaminants presents a risk to humans and animals. Specifically, the occurrence of drugs in aqueous ecosystems is related to the increase in antimicrobial resistance. Several methods to remove them have been studied but most have cost and toxicity drawbacks. Thus, the study of new eco-sustainable procedures is needed as the liquid–liquid extraction with hydrophobic solvents (ESs). In this study, we prepared six ESs mixtures with thymol (Thy) and octanoic acid (Oct) or decanoic acid (Dec) and evaluated their extractive ability in aqueous mixtures of quercetin (Q), nitrofurantoin (NF), or tetracycline (TC). In addition, we measured, correlated, and modelled both the solid–liquid equilibria of the two systems and seven thermophysical properties of the mixtures. From these calculations, we obtained the melting enthalpies of the eutectic points, isobaric thermal expansibilities, intermolecular free lengths, orientational dipolar parameters, thermodynamic properties of the surface, critical temperatures, and activation energies of viscous flow. The perturbed chain statistical associating fluid theory was found to be suitable for predicting the thermodynamic behaviour of these systems. Next, we determined the solubility of the three drugs both in water and in the eutectic mixtures, as well as the efficiency extraction (EE) of the latter. We obtained the highest extraction efficiency for the equimolar [Thy:Oct] mixture, which was the most polar solvent. The values were: EEQ=97.8%, EENF=84.9%, and EETC=95.0%. Further, performing the procedure with three cycles increased these values above 99%. The results showed the highest hydrophobicity for quercetin and the lowest for nitrofurantoin.

Understanding of molecular interactions between ethyl acetate and 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide: A thermophysical study

In this work, densities, speeds of sound and refractive index of pure and binary blends of 1-butyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide ionic liquid (IL) with Ethyl acetate (EtOAc) have been measured at various temperatures at atmospheric pressure 0.1 MPa. With the help of experimental results, a discussion is carried out on the molecular interactions and the effect of temperature on interactions through excess properties such as excess molar volumes, VmE, excess isentropic compressibility, κsE, excess speeds of sound, uE, excess molar isentropic compressibility, Ks,mE, excess isobaric thermal expansion, αpE. The excess properties are adequately fitted with the Redlich-Kister polynomial equation. The excess partial molar volumes, V¯m,1E and V¯m,2E and excess partial molar isentropic compressibility, K¯s,m,1E and K¯s,m,2E, excess partial molar volumes, V¯m,1°E and V¯m,2°E and excess partial molar isentropic compressibility, K¯s,m,1°E and K¯s,m,2°E of the components at infinite dilution also been measured. For a better understanding of molecular interactions, authors discussed with various cationic and anionic ILs with Ethyl acetate.

Liquid dibromomethane under pressure: a computational study

Molecular dynamics simulations have been performed on liquid dibromomethane at thermodynamic states corresponding to temperature in the range 268-328 K and pressure varying from 1 bar to 3000 bar. The interaction model is a simple effective two-body pair potential with atom-atom Coulomb and Lennard-Jones interactions and molecules are rigid. Thermodynamic properties have been studied, including the isobaric thermal expansion coefficient, the isothermal compressibility, the heat capacities and the speed of sound. The simulation results exhibit a crossing of the isotherms of the isobaric thermal expansion coefficient at about 800 bar in very good agreement with the prediction of an isothermal fluctuation equation of state predicting such a crossing in the pressure range 650-900 bar, though experimental results up to 1000 bar do not find any crossing.

Temperature, Pressure, and Length-Scale Dependence of Solvation in Water-like Solvents. I. Small Solvophobic Solutes.

We analyze the role of temperature, pressure, and solute's molecular size on the pattern of isochoric and isobaric solvation of small hard-sphere solutes in TIP4P/2005 water and in a water-like "Jagla" solvent exhibiting unusual thermodynamics. To this end, we employ molecular simulation to determine solvation free energies, isochoric solvation energies and entropies, isobaric solvation enthalpies and entropies, partial molecular volumes, and isothermal density derivatives of the solvation free energy along isobaric and isothermal paths covering solvent's stable liquid and supercritical states as well as supercooled and "stretched" liquid states. Results are found to be consistent with the most primitive scaled-particle theory and the Gaussian model of small-length-scale solvation. The temperature and pressure dependence of solvation quantities embraces solvent's water-like unusual thermodynamic behavior: its density is reflected in the solvation free energy; the isochoric solvation energy and entropy; and the isothermal density derivative of the solvation free energy, its isobaric thermal expansivity in the isobaric solvation enthalpy and entropy, and its isothermal compressibility in the partial molecular volume. The solute's size or length-scale dependence is found to combine with solvent's water-like behavior to produce the "convergence thermodynamics" picture characteristic of aqueous solutions of nonpolar solutes, which is unequivocally found here to be the mapping of the water-like density maximum into the isobaric solvation enthalpy and entropy versus temperature curves for a set of solutes of varying sizes.