Excess Thermodynamic Properties Research Articles

System-size effects in ionic fluids under periodic boundary conditions.

We investigate the system-size dependence of the thermodynamic properties of ionic fluids under periodic boundary conditions. Following an approach previously developed in the context of quantum Monte Carlo simulations of many-electron systems, we show that the leading-order finite-size artifact in the Coulomb energy per particle of a classical fluid of N structureless ions at given density and temperature is simply -kBT(2N)-1. Analytical approximations for the periodicity-induced size dependence of the excess thermodynamic properties of the fluid in the weak-coupling regime are obtained within the linearized Debye-Hückel theory. Theoretical results are compared with published simulations of the one-component plasma and our own simulations of a primitive-model electrolyte solution. Our work is directly relevant to estimating finite-size corrections in simulations of charged fluids comprising structureless ions embedded in continuous media. We outline in the Appendix how some of our formal results may be generalized to molecular fluids with mobile ions; e.g., electrolyte solutions with explicit solvent.

Molecular dynamics study of 2,2′-difurylmethane and n-propanol binary mixture

Thermodynamic properties and structural aspects of 2,2′-difurylmethane (DFM) (1) and n-propanol (2) binary mixtures have been investigated using molecular dynamics simulation. Thermodynamic properties such as density, isothermal compressibility, enthalpy of vaporization, molar volume and excess molar volume are reported. In most cases the observed experimental data as a function of DFM mole fraction, x1, is well reproduced. For neat systems there is better agreement between theory and experiment for n-propanol than DFM. However, the variation of excess molar volume with composition is well reproduced. Atom-atom and molecule-molecule center of mass radial distribution functions are used to study the structural properties. Evidence from the interspecies atom to atom radial distribution functions suggests the presence of weak hydrogen bonding through the n-propanol acidic hydrogen and the oxygen from one of the furan rings but no evidence was found for the interaction of acidic hydrogen and the π-electron system. The molecule-molecule coordination numbers reveal non-ideal mixing at x1=0.2and0.9 mixtures which is in excellent agreement with simulated excess thermodynamic properties. Both components are homogenously distributed in high mole fraction but n-propanol tends to form more clusters than DFM.

Thermodynamic properties of ring polyelectrolytes in the binding mean spherical approximation

Abstract A simple model for charged ring polyelectrolyte is proposed, to describe their thermodynamic properties. Starting from an analytical expressions previously obtained for charged chains within the binding mean spherical approximation, we present a method to determine suitable modifications in order to describe charged rings. It is shown that the electrostatic excess thermodynamic properties can still be computed from relatively simple formulas which involve a screening parameter ΓB.

Excess thermodynamic properties of glassforming liquids: The rational scaling of heat capacities, and the thermodynamic fragility dilemma resolved

With the overall objective of clarifying some perennial issues with the concept of liquid fragility, and with thermodynamic fragility in particular focus, we review the determination of excess thermodynamic properties of liquids as the temperature rises above Tg. We treat the compressibility first, as it is the one most commonly encountered in theory where it may be derived from the radial distribution function (specifically, from its Fourier transform (the structure factor) at zero wave vector), and is known to be proportional to the mean square density fluctuation. We show that the compressibility of glassforming liquids, and also the difference in compressibility between liquid and glass, always decreases as Tg is approached with the exception of a few water-like (anomalous) liquids. Secondly we examine the heat capacity which is favored in the analysis of glassforming liquid behavior. Contrasting with the compressibility, the excess heat capacity (determined by entropy fluctuations), mostly increases as temperature approaches Tg (with the same exceptions). But here we encounter the problem of the appropriate scaling of the measured molar quantity, which plagues comparisons of ∆Cp between different substances. We solve this problem by defining Cp as an entropy derivative and scaling by the absolute excess entropy at Tg - which avoids the need for “beads” or other artificial scaling methods. Finally, we revisit the subject of thermodynamic fragility, which has been discussed before using a related scaling strategy.

Phase equilibrium properties of binary mixtures containing a diesel compound (n-dodecane) + biodiesel compounds (ethyl hexanoate, ethyl decanoate and ethyl tetradecanoate)

The vapor pressures of three binary systems ethyl hexanoate (1) + n-dodecane (2), ethyl decanoate (1) + n-dodecane (2) and ethyl tetradecanoate (1) + n-dodecane (2) were measured by means of a static apparatus at temperatures between 373.15 and 453.15 K. The data were correlated with the Antoine equation. From these data, the molar excess Gibbs energies G E were obtained with Barker’s method and fitted to the Redlich–Kister equation. The excess Gibbs energy is positive for all the investigated constant temperatures and over the whole composition range. The Wilson equation was used and good results were obtained in the prediction of the total pressure and thermodynamic excess properties; however, deviations were observed with respect to the experimental and predicted G E, using UNIFAC (Dortmund) group contribution model.

Temperature of maximum density and excess thermodynamics of aqueous mixtures of methanol.

In this work, we present a study of representative excess thermodynamic properties of aqueous mixtures of methanol over the complete concentration range, based on extensive computer simulation calculations. In addition to test various existing united atom model potentials, we have developed a new force-field which accurately reproduces the excess thermodynamics of this system. Moreover, we have paid particular attention to the behavior of the temperature of maximum density (TMD) in dilute methanol mixtures. The presence of a temperature of maximum density is one of the essential anomalies exhibited by water. This anomalous behavior is modified in a non-monotonous fashion by the presence of fully miscible solutes that partly disrupt the hydrogen bond network of water, such as methanol (and other short chain alcohols). In order to obtain a better insight into the phenomenology of the changes in the TMD of water induced by small amounts of methanol, we have performed a new series of experimental measurements and computer simulations using various force fields. We observe that none of the force-fields tested capture the non-monotonous concentration dependence of the TMD for highly diluted methanol solutions.

Comments concerning "The density, the refractive index and the adjustment of the excess thermodynamic properties by means of the multiple linear regression method for the ternary system ethylbenzene-octane-propylbenzene"

This short communication presents the response to the comments published by William E. Acree Jr., Thermochim. Acta (2015), regarding the use of the equation Redlich and Kister by C. Lisa and collaborations in calculating the excess molar volume for ternary ethylbenzene (1)+octane (2)+propylbenzene (3) mixtures at 298.15K, 308.15K and 318.15K.

Excess Thermodynamic Properties for Binary Mixtures of Ionic Liquid 1-Ethyl-3-methylimidazolium Ethyl Sulfate and 2-Methoxyethanol from T = (298.15 to 328.15) K at Atmospheric Pressure

The density (ρ), speed of sound (u) and refractive index (n D) for pure [Emim][EtSO4], 2-methoxyethanol and their binary mixtures were measured using an Anton Paar vibrating tube density and sound velocity meter (DSA 5000 M) and automatic refractometer over the whole composition range as a function of temperature between 298.15 and 328.15 K in steps of 10 K at atmospheric pressure. Experimental values were used to calculate the excess values of molar volumes (\( V_{\text{m}}^{\text{E}} \)), partial molar volumes (\( \overline{V}_{\text{m}}^{\text{E}} \)), partial molar volumes at infinite dilution (\( \overline{V}_{\text{m}}^{{{\text{E,}}\infty }} \)), isentropic compressibility (\( \kappa_{S}^{\text{E}} \)), acoustic impedance (Z E), free length (\( L_{\text{f}}^{\text{E}} \)), speeds of sound (\( u_{{}}^{\text{E}} \)), internal pressure (\( \mathop \pi \nolimits_{i}^{\text{E}} \)), free volume (\( V_{\text{f}}^{\text{E}} \)) and deviations in refractive index ( \( \Delta_{\phi } n_{\text{D}} \)) for the binary mixtures. These properties were fitted to a Redlich–Kister type equation to obtain the binary coefficients and the standard deviations. The negative values of \( V_{\text{m}}^{\text{E}} \), \( \kappa_{S}^{\text{E}} \), \( L_{\text{f}}^{\text{E}} \),\( \alpha_{p}^{\text{E}} \), and \( V_{\text{f}}^{\text{E}} \) and positive values for Z E, \( u_{{}}^{\text{E}} \),\( \mathop \pi \nolimits_{i}^{\text{E}} \), and \( \Delta_{\phi } n_{\text{D}} \) indicate the existence of strong interactions between the components. This was further supported by IR spectroscopy analysis.

Speed of Sound, Density, and Related Thermodynamic Excess Properties of Binary Mixtures of 2-Pyrrolidone and N-Methyl-2-pyrrolidone with Acetonitrile and Chloroform

Densities and speeds of sound were measured for binary mixtures of 2-pyrrolidone or N-methyl-2-pyrrolidone with acetonitrile or chloroform at temperatures of (293.15 to 323.15) K and at atmospheric pressure, with uncertainties of 0.5 kg·m–3 and 0.5 m·s–1, respectively. From the measured speeds and densities, isentropic compressibilities and molar excesses of volume, isentropic compression, and thermal expansion were calculated. All of the excesses are negative, which is due to the geometries of the molecules and changes in the hydrogen bonding upon mixing. In the simplest case of the N-methyl-2-pyrrolidone + acetonitrile system, the negative excesses result only from the different sizes of the molecules because the components are incapable of forming either self- or cross-associates. For the other systems, the net effects of the formation and/or dissociation of the hydrogen bonds lead to bigger negative excesses of molar volume and thermal expansion. The negative excesses of compression are probably cause...

Relationship between the thermodynamic excess properties of mixing and the elastic moduli in the monazite-type ceramics

Using ab initio quantum chemistry we computed the excess thermodynamic properties and the elastic moduli for a series of monazite-type single substitution solid solutions (Ln1−xLnxPO4). We found that the Margules interaction parameters of all the solid solutions can be described by a simple function of the endmembers volume mismatch ΔV, i.e. W(kJ/mol)=0.616(ΔV(cm3/mol))2. We show that the obtained relationship could be also derived by considering the strain energy resulting from the substitution of cations of different sizes, knowing the Young's modulus and the volumes of endmembers. This indicates that the strain resulting from the structural incorporation of cations is a major factor responsible for arising of the excess properties in monazite-type ceramics. Our results show thus a way to estimate the excess thermodynamic properties of solid solutions from the structural and elastic parameters, namely the endmembers volumes and the Young's modulus, which could be easily measured or computed.

FT-IR Spectroscopic study of excess thermodynamic properties of liquid mixtures containing N-methylformamide with 2-alkoxyethanols at various temperatures

Densities, speeds of sound and viscosities were measured for the binary mixtures N-methylformamide (NMF) with 2-alkoxyethanols (2-methoxyethanol (ME), 2-ethoxyethanol (EE) and 2-butoxyethanol (BE)) at T=(303.15 to 318.15) K. These experimental data have been used to calculate excess volume (VE), excess isentropic compressibility (κsE), deviation in viscosity (∆η) and excess Gibbs free energy of activation of viscous flow (G⁎E). The excess partial molar volumes, V̅m,1E and V̅m,2E and excess partial molar volumes V̅m,1°E, and V̅m,2°E at infinite dilution have also been calculated. The variations of these properties with composition of binary mixtures suggest loss of dipolar association, difference in size and shape of the component molecules, dipole–dipole interaction and hydrogen bonding between unlike molecules. The excess parameters have been fitted to the Redlich–Kister equation and the results were analyzed in terms of acid–base interactions, hydrogen bond, and dipole–dipole interaction between unlike molecules. Further, the FTIR spectra have been recorded at 298.15K and found to be useful for understanding the presence of hydrogen bonding between oxygen atom of carbonyl group of N-methylformamide and hydrogen atom of the –OH group of 2-alkoxyethanols molecules in the present liquid mixtures. A good agreement is obtained between excess quantities and spectroscopic data.

Comments concerning “The density, the refractive index and the adjustment of the excess thermodynamic properties by means of the multiple linear regression method for the ternary system ethylbenzene–octane–propylbenzene”

The comment points out several mathematical shortcomings in the published paper by Lisa and coworkers, including the use of an incorrect form for the Redlich–Kister equation for a ternary system.

Densities of Fe–Ni melts and thermodynamic correlations

The densities of liquid Fe–Ni alloys were measured accurately by combination of an electromagnetic levitation technique and a static magnetic field. The static magnetic field suppressed the surface oscillation of the levitated sample droplet, which reduced the experimental uncertainty in the density measurement. Densities were determined over a wide temperature range and included a supercooled region. The densities of all Fe–Ni alloys investigated vary linearly with temperature over the range of measurements. The excess volumes were slightly positive over the entire composition range. The results were discussed within a thermodynamic framework using relationship between excess volume and thermodynamic properties such as excess Gibbs energy and enthalpy of mixing. The excess volume is correlated positively with excess Gibbs energy and enthalpy of mixing for various binary alloy systems.

Photoacoustic determination of speed of sound in binary mixtures of water and ethyl and methyl alcohol

The speed of sound in binary aqueous solutions of two alcohols by means of the pulsed photoacoustic technique has been determined. Hereby an analysis of the relationships of excess thermodynamic properties of the mixture to the speed of sound in it is presented. It is also shown that neither the Grüneisen coefficient nor the absorption coefficient of the mixtures are additive functions of the composition. The advantage of this method of speed determination lies in its inherent simplicity and the good precision attained. It can be used in tomography of water in different phantoms and potentially in tissues of biological origin.

FT-IR spectroscopic study of excess thermodynamic properties of liquid mixtures containing benzylalcohol with alkoxyalkanols

Densities (ρ) of pure liquids and their mixtures have been measured at T=298.15K to T=318.15K and 0.1MPa pressure over the entire composition range for the binary mixtures of benzylalcohol (BA) with 2-Methoxyethanol (ME), 2-Ethoxyethanol (EE), 2-Butoxyethanol (BE) by using Rudolph Research Analytical digital densitometer (DDH-2911 model). Further, the speed of sound (u) for the above said mixtures was also measured at T=298.15K and T=308.15K. Values of the experimental density were used to calculate the excess volumes (VE), in turn were compared with Redlich–Kister and Hwang equations. Isentropic compressibility (κS) and excess isentropic compressibility (κSE) were evaluated from experimental speed of sound and density data. Moreover, the experimental speed of sound was analysed in terms of theoretical models, namely Schaaff’s collision factor theory (CFT) and Jacobson’s free length theory (FLT). The experimental results are discussed in terms of intermolecular interactions between component molecules of binary mixtures and also FT-IR Spectroscopic studies.

Influence of alkyl group and temperature on excess thermodynamic properties of diethyl carbonate and their binary mixtures at 0.1 MPa

In this work, the experimental densities, ρ, and speeds of sound, u, of binary mixtures of diethyl carbonate (DEC) with the three isomers of xylene (ortho-, meta- and para-xylenes) were measured over the entire composition range at T=(298.15–323.15) K, and at atmospheric pressure (0.1MPa). From the experimental data, the excess molar volumes, VmE, excess isentropic compressibility, κsE, excess molar isentropic compressibility, κs,mE, and deviation in speed of sound, μD have been evaluated. Excess parameters were fitted to the Redlich–Kister polynomial equation to obtain the binary coefficients and the standard errors. Excess partial molar volumes (V¯m,1E and V¯m,2E) and their limiting values at infinite dilution (V¯m,10E and V¯m,20E) have been calculated from the experimental density measurements. Excess partial molar isentropic compressibilities, κ¯s,m,1E and κ¯s,m,2E of both components and their respective limits at infinite dilution, κ¯s,m,10E and κ¯s,m,20E, were analytically obtained using Redlich–Kister type equations.

The density, the refractive index and the adjustment of the excess thermodynamic properties by means of the multiple linear regression method for the ternary system ethylbenzene–octane–propylbenzene

The density (ρ) and the refractive index (n) have been experimentally determined for the ethylbenzene (1)–octane (2)–propylbenzene (3) ternary system in the entire variation range of the composition, at three temperatures: 298.15, 308.15 and 318.15K and pressure 0.1MPa. The excess thermodynamic properties that had been calculated based on the experimental determinations have been used to build empirical models which, despite of the disadvantage of having a greater number of coefficients, result in much lower standard deviations in comparison with the Redlich–Kister type models. The statistical processing of experimental data by means of the multiple linear regression method (MLR) was used in order to model the excess thermodynamic properties. Lower standard deviations than the Redlich–Kister type models were also obtained. The adjustment of the excess molar volume (VE) based on refractive index by means of the Multiple linear regression of the SigmaPlot 11.2 program was made for the ethylbenzene (1)–octane (2)–propylbenzene (3) ternary system, obtaining a simple mathematical model which correlates the excess molar volume with the refractive index, the normalized temperature and the composition of the ternary mixture: VE=A0+A1X1+A2X2+A3(T/298.15)+A4n for which the standard deviation is 0.03.

Current limitations of molecular dynamic simulations as probes of thermo-physical behavior of silicate melts

Molecular dynamic simulations offer promise as an essential tool, complementary to experiments, for expanding the reach of computational thermodynamics in igneous petrology by evaluating excess thermodynamic properties of multicomponent silicate melts. However, we present evidence suggesting that current practices in simulation may not achieve the precision needed to predict complex phase equilibria relevant to modeling the Earth’s interior evolution. We highlight the importance of quantification of the chemical short-range order in terms of cation-cation pairs in the melt and its impact on different kinetic aspects of molecular dynamic simulations. We analyze published molecular dynamic simulation studies of silicate melts to identify specific criteria and best practices for achieving and demonstrating equilibrium and producing accurate results. Finally, we propose a list of experimental and numerical investigations that need to be performed in the future to ensure full consistency between these two approaches to reduce the gap in our fundamental understanding of silicate melts between the atomic level and the macroscopic scale.

Effect of alkanol chain length on excess thermodynamic properties of p-cresol with 1-alkanol (C3–C8) at 298.15, 303.15, 308.15 and 313.15 K

The objective of the present study is to accredit the molecular interactions between p-cresol and 1-alkanols at different temperatures, based on the thermophysical properties such as densities (ρ) and speed of sound (u) data. To improve our understanding of the molecular interactions between 1-alkanols such as 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol and 1-octanol with p-cresol have been measured as a function of composition at different temperatures from (298.15 to 313.15) K and at atmospheric pressure. From these experimental data, the excess volumes (VE), isentropic compressibilities (ks) and excess isentropic compressibilities (ksE) have been calculated for 1-alkanols with p-cresol. The measured excess properties were correlated with the Redlich–Kister polynomial equation. The calculated properties were discussed in terms of molecular interactions between component molecules.

Water–Methanol Mixtures: Simulations of Mixing Properties over the Entire Range of Mole Fractions

Numerous experimental and theoretical investigations have been devoted to the hydrogen bond in pure liquids and mixtures. Among the different theoretical approaches, molecular dynamics (MD) simulations are predominant in obtaining detailed information, on the molecular level, simultaneously on the structure and the dynamics. Water and methanol are the two most prominent hydrogen-bonded liquids, and they and their mixtures have consequently been the subject of many studies; we revisit here the problem of the mixtures. An important first step is to check whether a classical potential model, the components of which are deemed to be satisfactory for the pure liquids, is able to reproduce the known thermodynamic excess properties of the mixtures sufficiently well. We have used the available BJH (water) and PHH (methanol) flexible models because they are by construction mutually compatible and also well suited to study, in a second step, some dynamic property characteristic of hydrogen-bonded liquids. In this article we show that these models, after a slight reparametrization for use in NpT simulations, reproduce the essential features of the excess mixing and molar properties of water-methanol mixtures. Furthermore, in the pure liquids, the agreement of the radial distribution functions with experiment remains as satisfactory as before. Similarly, the translation self-diffusion coefficients D are modified by less than 10%. In the mixtures, they evolve nonmonotonously as a function of mole fraction.