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Despite the widespread use of the 4:1 methanol–ethanol mixture as a hydrostatic medium by the high-pressure community, its equation of state (EOS) is usually substituted by that of pure methanol. Here we report accurate direct volumetric measurements of the room temperature EOS for this mixture up to 5 GPa. A brief description of the optical technique (imaging+interferometric) specifically developed for this purpose is given, as well as the general characteristics of the required miniature diamond anvil cell. Our results are compared with the available data of similar pure fluids’ EOS in the same pressure range. We find that there exist noticeable differences between the EOS of the mixture and that of pure methanol in terms of molar quantities.

We present direct measurements of the isothermal compressibility (κT) and thermal expansion coefficient (αp) of liquid methanol using an expansion technique. The measurements of κT were carried out along six isotherms from (208.17 to 298.16) K at pressures up to 101 MPa. For αp, we have measured four isobars from (0.59 to 80.03) MPa from 195 K up to 300 K. Our experimental results of αp(T) for the 0.59 MPa isobar exhibit a minimum around 224 K. A clear shift of the minimum to higher temperatures is observed as the pressure increases along the different isobars. Interestingly, the minima for the isobars of αp(ρ) take place within a narrow range of densities, around 26.5 mol·dm-3 (about 3.15 times the critical density).

In a previous work, we analysed some regularities found in the behaviour of the thermal expansion coefficient, αp, in compressed liquids. We confirmed that a given liquid presents a characteristic pressure range in which the condition is fulfilled within a narrow range of reduced densities. We also found that the density at which the condition is satisfied, ρα, decreases with temperature, a key feature not described before. Earlier studies by other authors suggested that similar regularities are expected for the reduced bulk modulus, B. We present here a detailed analysis of the temperature and density dependence of B from existing experimental results at high pressures. Several liquids have been analysed: argon, krypton, xenon, ethylene, tetrafluoromethane, trifluoromethane, carbon dioxide, carbon disulfide, n-butane, n-hexane, toluene, ethanol, 1-hexanol, m-cresol, and quinoline. We locate that the density ρB that fulfils the condition occurs at a particular region of the phase diagram, between 3.4 and 2.4 times the critical density of each liquid. Interestingly, the previously found density ρα is close to ρB, in a similar region of the reduced phase diagram. However, we note that ρB typically decreases to a lesser extent with temperature than ρα. In addition, we have found that ρB(T) behaves in a parallel fashion for the different liquids, showing larger values of ρB as the complexity of the molecules increases. These findings provide a strong basis for developing general equation of state models to describe the behaviour of liquids in the high-pressure regime.

We analyse here the thermodynamic behaviour of the thermal expansion coefficient for a number of liquids. The purpose of this work is to provide some general rules to develop equations of state models meeting the following criteria: thermodynamic consistency, generality, predictive power and accuracy to represent derived properties over wide ranges of pressure and temperature. The liquids included into our analysis have been selected to meet two criteria: (1) available experimental data over wide ranges of pressure and temperature (from the melting point up to the critical point), and (2) liquids composed of molecules with different geometries and interactions.

A general method to include temperature effects into the equation of state (EOS) of solids is discussed. A universal model based on a pseudo-spinodal approach is used to predict the pressure and temperature dependencies of the thermodynamic properties for a variety of solids: n -H 2 , Ar, Kr, Xe, NaCl, LiF, NaF, KCl, CsCl, Li, Na, K, Rb, Cs, Al, Fe, Cu, Zn, Ag, Cd, Pt, Au, and Pb. The predictive capabilities of the complete EOS are discussed and compared with available models.

We provide evidence of a universal equation of state for solids using a pseudospinodal hypothesis. A simple model to estimate the pseudospinodal curve is presented. This model combined with a previously reported (isothermal) volumetric equation [Baonza et al., Phys. Rev. B 51, 28 (1995)] yields a complete equation of state applicable over the whole range of temperature. The resulting equation appears to be a well-behaved equation of state over the whole range of temperatures using a single reference thermodynamic state of the solid at atmospheric pressure as input data. Comparison with experimental results of molar volume, bulk modulus, and thermal- (volumetric) expansion coefficient are presented. Comparison with previous equations of state are also presented and discussed. Our results imply that the thermodynamics of any solid are governed by its pseudospinodal curve. \textcopyright{} 1996 The American Physical Society.

Experimental excess volume, surface tension and isothermal compressibility measurements at atmospheric pressure are reported for ethanol–methylcyclopentane at 298.15 K. These data have been used to estimate the molar volume of the mixture up to 200 MPa through a novel procedure. Surface tension measurements at 293.15 K for carbon disulfide–tetramethylsilane are also reported. These data, together with measurements of molar volume and isothermal compressibility at atmospheric pressure previously reported for this mixture, have been used to make an analogous study up to 100 MPa. Comparison with experimental data is rather satisfactory for both systems. Differences between experimental and calculated volumes are commonly less than 1%, which allow us to predict adequately the pressure behaviour of the molar excess volume.

Some experimental studies indicate that the isothermal compressibility, κT, of molecular liquids follows a power law up to very high pressures along isothermal paths. We show here that the high-pressure behavior of κT can be characterized from surface tension and κT data measured at low pressures. Our method is based on a pseudospinodal hypothesis. Comparison with experimental is satisfactory up to very high pressures for different molecular liquids. The results are also studied in terms of the reduced bulk modulus. B. Our method reproduces adequately the intersections experimentally found for the isotherms of B versus molar volume of molecular liquids.

Most of useful estimation techniques for surface tension of liquids are based on empirical correlations and general methods with molecular basis are rare in the literature. In this paper we show how combining an expression derived from the hole theory of Furth with an statistical-mechanical based equation of state, an estimation of surface tension and its behavior with temperature is easily obtained.

Accurate thermal expansion coefficient αp, speed-of-sound and density measurements found in the literature have been used to characterize the general behavior with pressure of the constant pressure heat capacity Cp of benzene and toluene. The results agree well with direct measurements of Cp found in the literature. Indirect methods for estimating Cp at high pressures are discussed. αp results obtained with an expansion technique using a differential method have been used to characterize the high-pressure behavior of Cp for mesitylene.

Experimental pρT measurements and derived thermodynamic properties of p-xylene (1,4-dimethylbenzene) have been obtained with an expansion technique for temperatures between 288 and 303 K and pressures up to 43 MPa, or freezing pressure when lower. The solid-liquid coexistence curve of this compound was also measured up to 40 MPa. The experimental results have been correlated in terms of a recently derived equation of state, which is introduced here and has been used to calculate the isothermal compressibility, κT, and the thermal expansion coefficient, αp, as functions of pressure and temperature. The equation of state depends only on six parameters, all of which are physically meaningful. Comparisons of several properties show good agreement with literature values.

pρT values for liquid o-xylene have been measured with an expansion technique at temperatures between 258 and 298 K and pressures up to 108 MPa. Isothermal compressibility and thermal expansion coeffcient data are reported as functions of pressure and temperature. The pρT results have been used to test the performance of two recently developed equations of state and to study the physical significance of their characteristic parameters. The extrapolation capabilities of both equations have been checked with experimental results from the literature at higher pressures and temperatures.

Experimental pρT measurements of m-xylene obtained with an expansion technique are reported from 230 to 298 K and up to 110 MPa, or freezing pressure when lower. The experimental results have been correlated in terms of a recently proposed equation of state which has been used to calculate the isothermal compressibility, κT, and the thermal expansion coefficient, αp, as functions of pressure and temperature. Experimental density results for liquid toluene, which was used to calibrate our experimental device, are also reported for the isotherms of 223 and 303 K. The ability of simple power functions recently proposed to correlate high-pressure results has been tested. The extrapolation capabilities of these functions have been confirmed using experimental results from the literature for the two compounds studied.

Experimental and theoretical studies suggest that the thermal expansion coefficients α p of liquids follow a power law up to extremely high pressures along isothermal paths. Accurate experiments reveal that intersections between α p isotherms occur at high pressure for many liquids. It is shown how the high-pressure behavior of α p can be accurately predicted for real liquids from surface tension and low-pressure α p measurements. The method proposed here is based on the assumption that the spinodal curve does exist and can be estimated from surface tension measurements using Furth's hole theory.

Molar densities have been measured by using an expansion technique at pressures up to 104 MPa and temperatures from 198 to 298 K for the mixture {x CS2 + (1-x) Si(CH3)4}(1) over the whole composition range. Several thennodynamic properties (isothermal compressibility, thermal expansivity, and molar internal energy, enthalpy and entropy increments relative to liquid at saturation) have been directly obtained from the experimental densities. The isothermal compressibility and the thermal expansivity are both smooth functions of pressure, temperature and composition, although the isotherms of the thermal expansivity exhibit a characteristic crossover at high pressures. The intersection of isotherms of thermal expansivity seems to occur at a single point of the (p,αp) diagram, showing a nearly linear dependence with the composition.

Studying the behavior with pressure and temperature of thermal expansivity data derived from (p,p,T) measurements of liquids, we found that a previously derived analytical equation of state is inapplicable under certain thermodynamic conditions. The main obstacle is that these conditions are determined by characteristic constants of the liquid under study. Following the same scheme used to derive the original equation of state, we propose a new analytical expression which removes this restriction. Three different substances have been used to test the ability of the new equation of state to represent the volumetric properties of compressed liquids

The Deiters equation of state has been used to predict the vapor-liquid equilibrium and second virial coefficient for several pure substances. The equation of state depends on three characteristic parameters which can be calculated from the critical constants. A general procedure to determine the characteristic parameters is reported. The predictions are very satisfactory, being within the experimental uncertainties in most cases.

We use a dynamic light scattering technique to measure both polarized (VV) and depolarized (VH) spectra of liquid diphenylmethane (DPM) between 288 and 362 K, covering both normal and supercooled liquid ranges. Our results allow extracting information on structural relaxation processes, rotational motions, rotation–translation couplings, and molecular reorientation phenomena in liquid DPM. The VV spectra are modeled according to the microscopic theory of Wang [J. Chem. Phys. 70, 3796 (1979)], which assumes that a structural relaxation process dominates the spectrum. We find that the relaxation time of the structural relaxation in DPM follows an Arrhenius behavior. The Rayleigh dip was observed in the VH spectra, which are described using the Andersen–Pecora [J. Chem. Phys. 54, 2584 (1971)] theory. Our results are discussed in terms of the rotation–translation coupling parameter, which we find independent of temperature over the experimental range. The collective reorientation time also follows an Arrhenius behavior with temperature. Finally, we calculate the hydrodynamic volumes for the reorientation process from geometric molecular models in two hydrodynamic limits: slip and stick boundary conditions. Our results suggest that the DMP molecule reorientates in quasi-slipping conditions in the bulk liquid.

We recently proposed an isothermal equation of state that was successfully applied to study the high-pressure behavior of molecular liquids. In this work we extend its applicability to liquid metals, polymers, molten salts, and solids. The possibility of considering this equation as an alternative to long-standing equations such as those of Tait and Birch-Murnaghan is emphasized. This suggestion is firmly supported by comparisons with experimental data up to pressures of several GPa. A new physical interpretation of the pressure coefficient of the Tait equation ${\mathit{B}}_{\mathit{T}}$ is given. It can be identified to the divergence pressure along a pseudospinodal curve. We also compare the performance of our equation with the most successful equations of state used to represent isothermal data of solids, with excellent results. Our equation can be applied to systems with phase transitions. An interesting observation is that it seems that the different pseudospinodal curves obtained for the different phases can be put together into the same curve except for characteristic jumps occurring at the phase transitions.

Mechanical coeffecients of liquids play an important role in the understanding of the physics of fluids. There is a relative small number of undergraduate experiments dealing with thermodynamic properties of pure liquids and liquid mixtures. In fact, it is difficult to find experiments other than direct determination of liquid molar volumes or the molar excess volume for binary mixtures, which are usually measured by pyknometry. This paper describes a simple experiment designed to measure the isothermal compressibility and the thermal expansion coefficient of liquids. The experiment is based on an expansion principle and can be carried out with a rather simple experimental device. Additional features of the method and advanced experiments are discussed.

Vapour pressures and excess volumes for the hexafluorobenzene—n-hexadecane system and vapour pressures for the hexafluorobenzene—benzene—n-hexadecane system have been measured at 298.15 K. Thermodynamic consistency of the data has been checked using a Pade approximation for the binary system, and a new expression for the excess Gibbs energy of the ternary system. The new expression compares favourably with others previously proposed in the literature.

The Rayleigh ratio has been obtained for the following mixtures of non-electrolytes that show “w-shape” CEp vs. x curves: Nitrobenzene + n-Heptane, 1,4-Dichlorobutane + n-Heptane and Acetone + n-Dodecane. From them, the concentration-concentration correlation function Scc(0) has been calculated, as well as the excess Gibbs energy. It has been found that a clear tendency to homocoordination is present in all the mixtures studied. There is a rough correspondence between the concentration at which the maximum of the Scc(0) curves occur and those at which the negative curvature regions exist in the CEp curves. Also the larger the value of max. Scc(0) the more intense the “w-shape” effect. Despite size differences between the components and specific interactions which complicate the connection between Scc(0) and CEp, an analysis in terms of simple mean field models supports the view that the systems which show “w-shape” CEp curves still feel the effects of the more or less distant UCST. Hence Scc(0) is proposed as an indicator of the “w-shape” CEp.

Expansion coefficients (α), thermal pressure coefficients (γ), isothermal compressibilities, densities and heat capacities have been measured at 25 °C for pure components and the following mixtures: 1-chloronaphthalene with the series of normal alkanes (n-Cn) where n= 6, 8, 10, 12, 14, 15 and 16, and with a series of highly branched alkanes (br-Cn), 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane and 2,2,4,4,6,8,8-heptamethylnonane. With these data the following first- and second-order mixing quantities are reported: VE, dVE/dT, dVE/dP, Δ(γVT), CEp, Δ(αγVT) and ΔCν. Excess enthalpies, HE, for 1-chloronaphthalene–br-Cn, CEp for p-xylene–n-Cn(n= 8, 10 and 14), 1-chloronaphthalene–cyclohexane and 1-methylnaphthalene–n-C12 are also reported. VE and dVE/dT are strongly negative, and dVE/dP are positive, for the lower n- and br-Cn, becoming smaller for higher alkanes. Flory theory gives excellent predictions for each quantity with both series. The mixing function, Δ(γVT), deviates from the equality Δ(γVT)=–HE which is predicted by the Flory theory and other theories which assume van der Waals behaviour. Contrasting with cyclohexane–n-Cn and benzene–n-Cn, where –Δ(γVT) > HE, 1-chloronaphthalene with n-Cn gives –Δ(γVT) 8. The excess heat capacity CEp is anomalously positive for the n-Cn series and has higher values than for br-Cn. CEp equimolar values show a maximum against the carbon number n; similar behaviour was found for Δ(αγVT). ΔCν=CEp–Δ(αγVT) values are strongly positive for both series of alkanes. The results are explained by temperature-sensitive ordering of (2–2) and (1–2) contacts. The (2–2) order between long-chain alkanes is destroyed on mixing, giving negative contributions to dVE/dT, Δ(γVT) and CEp, as in cyclohexane and benzene–n-Cn. For 1-chloronaphthalene–n-Cn(1–2) compensatory order formed in solution has the opposite effect, producing –Δ(γVT) 0.

We recently proposed an isothermal equation of state that was successfully applied to study the high-pressure behavior of solids. Later, we developed a simple model to include temperature effects on the equation of state. In the present work we consider the prediction capabilities of the complete equation of state in the entire p-V-T surface of a solid. Our predictions have been compared with experimental data up to pressures of several GPa and temperatures between zero and temperatures rather higher than those of melting. We also compare the performance of our equation against the most successful equations of state proposed in the literature, with excellent results. The isothermal equation of state provides us an adequate representation of experimental pressure-volume data and a simple volume dependence for the Gr\"uneisen parameter. The equation needs only four parameters evaluated at room pressure at a single reference temperature. \textcopyright{} 1996 The American Physical Society.

The excess volumes of C6F6 and C6H5F+an octane isomer (n-octane, cyclooctane, 2,2,4-trimethylpentane) have been measured at 25°C. The equimolar values increase from 2,2,4-trimethylpentane to n-octane to cyclooctane. The present results cannot be explained in terms of the scheme developed by Patterson for other alkane mixtures. Comparing the present results with others in the literature, the effect of the dipolar moment of the aromatic compound seems to be more complex than in previous studies of polar+non-polar components. The results have been analyzed in terms of two generalized van der Waals models, and a semiempirical equation of state. The results range from poor to fair.

We have recently shown that the high-pressure behavior of the isothermal compressibility, κT, and the thermal expansion coefficient, αp, can be characterized for molecular liquids from low-pressure measurements of these quantities together with surface tension data. The quality of the estimation was good enough to characterize the pressure behavior of the molar volume using a reference volume measured under orthobaric conditions. The same scheme is used here to predict the molar volume of some binary mixtures at different compositions as a function of pressure. Agreement with experimental data is good enough to predict the high-pressure behavior of the molar excess volume. © 1995 American Chemical Society.

The excess volume of hexafluorobenzene (C6F6)–2,2,4-trimethylpentane (2,2,4-TMP) has been measured at 298.15 K as well as the vapour pressures at 298.15, 323.15 and 348.15 K. From the latter, the excess Gibbs energies have been calculated, and the excess enthalpies have been estimated through the Gibbs–Helmholtz equation. The comparison with similar data for binary systems involving benzene (C6H6), C6F6, 2,2,4-TMP and cyclohexane (c-C6H12) shows that c-C6H12 and 2,2,4-TMP have quite different volumetric and entropic behaviours when mixed with C6F6, whilst they are almost equivalent when mixed with C6H6. Finally, the vapour pressures have been measured and the excess Gibbs energies calculated at 298.15 and 323.15 K for the ternary system C6F6–C6H6–2,2,4-TMP.

Expansion coefficients (α), thermal pressure coefficients (γ), isothermal compressibilities, densities and heat capacities have been measured at 25 °C for pure components and the following mixtures: 1-chloronaphthalene with the series of normal alkanes (n-Cn) where n= 6, 8, 10, 12, 14, 15 and 16, and with a series of highly branched alkanes (br-Cn), 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane and 2,2,4,4,6,8,8-heptamethylnonane. With these data the following first- and second-order mixing quantities are reported: VE, dVE/dT, dVE/dP, Δ(γVT), CEp, Δ(αγVT) and ΔCν. Excess enthalpies, HE, for 1-chloronaphthalene–br-Cn, CEp for p-xylene–n-Cn(n= 8, 10 and 14), 1-chloronaphthalene–cyclohexane and 1-methylnaphthalene–n-C12 are also reported. VE and dVE/dT are strongly negative, and dVE/dP are positive, for the lower n- and br-Cn, becoming smaller for higher alkanes. Flory theory gives excellent predictions for each quantity with both series. The mixing function, Δ(γVT), deviates from the equality Δ(γVT)=–HE which is predicted by the Flory theory and other theories which assume van der Waals behaviour. Contrasting with cyclohexane–n-Cn and benzene–n-Cn, where –Δ(γVT) > HE, 1-chloronaphthalene with n-Cn gives –Δ(γVT) 8. The excess heat capacity CEp is anomalously positive for the n-Cn series and has higher values than for br-Cn. CEp equimolar values show a maximum against the carbon number n; similar behaviour was found for Δ(αγVT). ΔCν=CEp–Δ(αγVT) values are strongly positive for both series of alkanes. The results are explained by temperature-sensitive ordering of (2–2) and (1–2) contacts. The (2–2) order between long-chain alkanes is destroyed on mixing, giving negative contributions to dVE/dT, Δ(γVT) and CEp, as in cyclohexane and benzene–n-Cn. For 1-chloronaphthalene–n-Cn(1–2) compensatory order formed in solution has the opposite effect, producing –Δ(γVT) 0.

We have measured VE at 298.15 K for the systems formed by 2,2,4-trimethylpentane or n-octane or cyclo-octane, with chlorobenzene, 1,2-dichlorobenzene and 1,3-dichlorobenzene. The results can be qualitatively understood in terms of the p* and free-volume contributions to the excess functions. However, the effects of polarity and of the shape of the molecules are not as clear as in other studies reported in the literature.Whereas Deiters' equation of state fits the results of each system well, it does not predict the observed change in VE when the octane isomer is changed. On the other hand, generalized van der Waals, and a lattice-with-holes model, correctly predicts such a variation, although the quantitative agreement is poor.