Pressure-volume Isotherms Research Articles

Improved Prediction of Saturated and Single-Phase Liquid Densities of Water through Volume-Translated SRK EOS

The existing equation of states (EOSs) cannot well reconcile the calculation accuracy and the computational cost for reproducing liquid volumes of water. In this study, we propose a series of improved volume translated Soave-Redlich-Kwong (VT-SRK) EOSs to achieve more accurate volumetric calculation for water with little additional computational cost. The overall average absolute percentage deviation of the saturated liquid molar volume for water yielded by the proposed 4-parameter VT-SRK EOS is 0.26; this calculation error is much lower than the counterpart provided by our previously proposed 3-parameter VT-SRK EOS (1.24) and close to the uncertainty in the pseudo-experimental data reported by NIST (0.1%). After adopting the translated distance function, the proposed 5-parameter VT-SRK EOS provides a more accurate determination for the single-phase liquid volume of water over a wide temperature/pressure range and leads to the crossover of pressure-volume isotherms only at extremely high pressures. The proposed 4-parameter VT-SRK EOS also helps to improve the volumetric prediction for carbon dioxide, while the proposed 5-parameter VT-SRK EOS performs well in improving the density prediction for associating fluids. Moreover, we extend the proposed 5-parameter VT-SRK EOS to mixtures through conventional mixing rules, finding that the VT-SRK EOS provides reliable volume predictions for the aqueous solutions examined in this study.

Material Point Method Simulation of the Equation of State of Polymer-Bonded Explosive under Impact Loading at Mesoscale

Mesoscale simulation using the material point method (MPM) was conducted to study the pressure–volume (PV) variations of Octahydro-1,3,5,7-Tetranitro-1,2,3,5-Tetrazocine (HMX)/Estane polymer-bonded explosive (PBX) under impact loading. The PV isotherms and Hugoniot data were calculated for the different porosities and binder volume fractions. The PV isotherms were used to determine the parameters for the Birch– Murnaghan equation of state (EOS) for the PBX. From the EOS, the isothermal bulk modulus (K0) and its pressure derivative (K′0) were calculated. Additionally, the pseudo particle velocity and pseudo shock velocity variations were used to obtain the bulk wave speed c and dimensionless coefficient s for the Mie–Grüneisen EOS. The simulations provide an alternative approach for determining an EOS that is consistent with experimental observations.

Determination of Hildebrand solubility parameter for pure hydrocarbons by incorporating temperature-dependent volume translation into Peng-Robinson equation of state

To improve the prediction accuracy of solubility parameters of pure hydrocarbons, we incorporate recently proposed temperature-dependent volume translation models into PR-EOS. Four representative volume translation models have been chosen in the present study. On the basis of the different volume-translated EOSs, we derive a set of corresponding equations used for predicting solubility parameter for pure hydrocarbons. Experimentally derived solubility parameter of several hydrocarbons is used to examine the accuracy of predicted solubility parameter by different volume-translated EOSs. Results show that all the temperature-dependent models provide more accurate prediction than the uncorrected PR-EOS model. Magoulas and Tassios (1990) model demonstrates the highest accuracy among the five models. Shi et al. (2018) model is recommended for solubility parameter prediction as it does not lead to the crossover of pressure-volume isotherms over a wider range of temperature and pressure than Magoulas and Tassios (1990) model.

Isospin-dependent phase diagram of nuclear matter

In this article we obtain the phase diagram of nuclear matter extending it from the traditional two-dimensional density-temperature plane to three-dimensional space of density, temperature, and isospin asymmetry. We identify the liquid-gas coexistence region by means of Maxwell constructions over pressure-volume isotherms. Such pressure-density equations of state were constructed from data obtained from interpolating results from molecular dynamics simulations of infinite nuclear systems in the liquid phase those of Fermi gases at low (sub-saturation) densities. The molecular dynamics results were used to obtain the energy per nucleon and pressure for systems with densities and temperatures in the ranges ρ=0.01 to 0.2 fm−3, T between 1 and 15 MeV, and with isospin content of x = Z/A = 0.3, 0.35, 0.4, 0.45 and 0.5. The results indicate that symmetric and asymmetric matter are self-bound and show a coexistence region that extends, approximately, to densities of up to ρ0/2, temperatures of up to 16 MeV, and down to proton fractions of 13%.

Quantum effect on adsorption of fluids in slit pores: A DFT study

In this paper, the Wigner-Kirkwood quantum theory and the Weeks-Chandler-Andersen (WCA) effective diameter method in Classical DFT are employed to account for the effects of quantum corrections on the Helmholtz free energy of bulk and confined fluids. Initially, experimental data are exploited toward accurate prediction of pressure-volume isotherms and vapor-liquid equilibrium in bulk fluids. In the second part, the effects of quantum correction on the structure and thermodynamic properties of fluids confined in slit pores are investigated. Our results show that quantum effects may come into account by considering the effective size of the particles and also intermolecular interaction which both of them have direct effects on the density distribution of molecules in the slit pore. Furthermore, the excess adsorption of fluids at a fixed bulk density is shown to increase with quantum effect, but this trend is reversed with increasing wall fluid interaction because of the entropy and energy effects. Also, it is found that the excess adsorption and interfacial tension of the fluid against the solid surface of fluids exhibit oscillatory behaviors with maximum and minimum values for half integer and integer values of pore width. This oscillatory behavior disappears at high values of pore width with increasing quantum effect. Another finding of the present study indicates that the interfacial tensions of the fluid against the solid surface for a classical fluid are negative but quantum effect increases it and shifts its sign to positive. Finally, it is shown that the locus of phase transition is shifted toward higher bulk densities as a result of increasing quantum effect.

Criterion for determining crossover phenomenon in volume-translated equation of states

Volume translation is widely adopted in cubic equation of state (CEOS) to achieve more accurate density predictions for pure compounds and mixtures. Previous research reveals that a temperature-dependent volume-translated EOS could result in crossing of pressure-volume isotherms for a pure compound, which leads to an anomalous behavior that the predicted molar volume for a pure component can possibly be lower at a higher temperature at an isobaric condition. Such crossover phenomenon fails to consistently predict the thermodynamic properties of a pure compound, e.g., giving a negative isobaric thermal expansivity. In this study, we develop a concise criterion to judge whether a volume-translated EOS will result in crossover issues, and if so, the extent of the temperature and pressure range over which the crossover phenomenon occurs. The recently proposed volume translations are evaluated on the basis of the developed criterion. For the various types of temperature-dependent volume translations, we obtain the specific temperature/pressure conditions over which there is certainly no crossover phenomenon.

Influence of dehydration rate on cell sucrose and water relations parameters in an inducible desiccation tolerant aquatic bryophyte

During desiccation, plant cells are subjected to very low water potentials. Osmoregulation through increase of soluble materials (e.g. soluble sugars, compatible inorganic ions) is a response to the decreasing turgor pressure in the cells. In bryophytes, sucrose acts as an osmolyte and also stabilizing membranes and proteins through vitrification. We used psychrometric measurements in the aquatic bryophyte Fontinalis antipyretica Hedw. to construct pressure–volume isotherms and determine the water relations parameters under fast and slow dehydration rates. Sucrose was also quantified. The starting hypothesis was that a slow dehydration rate would increase sucrose concentration, thereby decreasing the osmotic potential at turgor loss point, and would also increase cell wall elasticity, postponing turgor loss and allowing time for induction of molecular and structural acclimation mechanisms. In fact, we found that slowly dehydrated samples presented more elastic cell walls, allowing cells to shrink and maintain turgor, helping to better preserve their metabolic functions and therefore to induce desiccation tolerance (DT). On the other hand, in fast dehydrated samples the osmotic potential at turgor loss point decreased, indicating the activity of osmoregulation processes, possibly connected to the increase observed in sucrose content. Upon rehydration, fast dried samples lost 50% of the sucrose through leakage due to cell membrane rupture, while slow dehydrated leaves maintained their sucrose content constant. DT appears to be achieved through slow dehydration, meaning that a high sucrose content alone does not contribute to DT establishment. Moreover, in natural conditions external water can be maintained at very high values due to the life form of F. antipyretica, which grows in long and compact floating stems in streams, allowing a slow dehydration rate required for induction of other DT mechanisms.

Liquid-liquid phase transition in a two-dimensional system with anomalous liquid properties

The phase diagram of the two-dimensional particles interacting through a smooth version of Stell-Hemmer interaction was studied using Monte Carlo computer simulations. By evaluating the pressure-volume isotherms, we observed liquid-liquid, liquid-gas phase transitions and three stable crystal phases. The model shows the liquid-liquid critical point in stable liquid phase and is confirmed by observing properties of other thermodynamic functions such as heat capacity and isothermal compressibility, for example. The liquid-gas and the liquid-liquid critical points were estimated within the thermodynamic limit.

Liquid-Liquid Transition in Supercooled Silicon Determined by First-Principles Simulation

First-principles molecular dynamics simulations reveal a liquid-liquid phase transition in supercooled elemental silicon. Two phases coexist below Tc approximately 1232 K and above pc approximately -12 kB. The low-density phase is nearly tetracoordinated, with a pseudogap at the Fermi surface, while the high-density phase is more highly coordinated and metallic in nature. The transition is observed through the formation of van der Waals loops in pressure-volume isotherms below Tc.

Salt tolerance in a Juncus roemerianus brackish marsh: Spatial variations in plant water relations

Abstract Halophytes residing in tidal marshes are often subjected to intense and varying environmental demands. These variations may occur in a matter of hours, with tidal-induced changes in hydrology and soil chemistry (including soil oxygen status, redox potentials, and salinity). Juncus roemerianus has been shown to occupy three dissimilar marsh zones, including lower marsh with minimally diluted saline waters, mid-marsh which undergoes periodic freshwater dilutions of tidal waters, and upper marsh which is principally maintained by upland freshwaters. The purpose of this study was to discern spatial patterns in plant water status of J. roemerianus . Leaf water potentials ( ψ leaf ) were 1–2 MPa less than soil-osmotic potential ( ψ π soil ), with the greatest ψ leaf (i.e., most negative; ca. − 4 MPa) generated within the lower marsh as plants experienced the highest salinities (18 ppt; during low tide). There was a 3–12% increase in relative water content ( θ ) in mid-marsh plants, in comparison to both lower- and upper-marsh individuals. Pressure–volume isotherms showed that plants along the shoreline (i.e., lower-marsh) had lower osmotic potential at full saturation ( ψ π sat ), lower osmotic potential at turgor loss point ( ψ π tlp ), and elevated bulk modulus of elasticity ( ϵ ). Whereas, no spatial differences in water content at turgor loss point ( θ tlp ) and symplastic water fraction ( θ sym ) were observed among the three marsh zones. Additionally, morphological and plant mass characteristics, including stomatal size, stomatal density, leaf abundance, and above-ground biomass, were greater in lower marsh plants compared to other two marsh zones. Overall, this study demonstrates the importance of soil–water salinity (as ψ π soil ) in shaping spatial variations in plant water status within a J. roemerianus brackish marsh.

Exact matrix computation of the statistical mechanics of a cell model of hard sphere phase behaviour

An exact calculation of the statistical mechanics of a cell model of hard-sphere isotherm behaviour is presented. Our calculation attributes the observed steps in the pressure–volume isotherms to entropic effects caused by the volume of space excluded by the hard core.

Two-phase regime in the magnetic field–temperature phase diagram of a type-II superconductor

Abstract The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of V 3 Si have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However, the magnetic moment–magnetic field isotherms are reversible and exhibit features that formally resemble the pressure–volume isotherms of the liquid–gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The two phases are disordered vortex configurations with the same magnetization, but with different vortex densities. The entropy change, determined from the data using the Clausius–Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases.

Les systèmes hétérogènes « eau–zéolithe hydrophobe »: de nouveaux ressorts moléculaires

Pressure–volume isotherms have been determined for three heterogeneous ‘water–zeolite’ systems. The first two concern hydrophobic purely siliceous zeolites: silicalite-1 (F −) and zeolite β (F −); the third comprises a more hydrophilic commercial zeolite of the type ZSM-5. The P– V diagram for the water–silicalite-1 (F −) system is characterized by a plateau corresponding to the intrusion of water inside the pores of the solid. During the release the phenomenon is reversible. This system, which is able to accumulate and restore superficial energy, constitutes a molecular spring. For zeolite β, the P– V curve displays a plateau during the compression, but during the release, the phenomenon is not reversible. In that case, the system absorbs mechanical energy and acts as a bumper. The third system, based on the more hydrophilic ZSM-5 zeolite shows a linear isotherm without any plateau. These results open new applications perspectives in the field of the energetics for hydrophobic zeolites in contact with water. To cite this article: V. Eroshenko et al., C. R. Physique 3 (2002) 111–119

Thermodynamics of n-Alkane Mixtures and Polyethylene−n-Alkane Solutions: Comparison of Theory and Experiment

We have applied the lattice Born-Green-Yvon theory to the study of hydrocarbon mixtures. In doing so we have fit pure component data in order to determine characteristic parameters for the pure fluids and have used the geometric mean approximation for the mixed-segment interaction energy. As a result, we have been able to make predictions for a wide variety of solution properties without fitting any data on the mixtures and have compared our predictions with experimental results. For binary alkane solutions made from combinations of n-hexane, n-octane, n-decane, and n-hexadecane we have found excellent agreement between theory and experiment for pressure-volume isotherms, volume changes on mixing and its pressure dependence, and equilibrium solution vapor pressures as a function of composition and temperature. For polyethylene-n-alkane solutions we have been able to predict the lower critical solution temperature and its dependence on the chain length of the alkane solvent, as well as the full coexistence curve and its variation with the polymer molecular weight.

Changes in water relations for leaves exposed to a climate-warming manipulation in the Rocky Mountains of Colorado

Relative water content (RWC) and water potential were compared for leaves of several plant species exposed to a warming manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, Colorado, USA, to test the hypothesis that species-specific changes in water relations parameters will occur in response to future increases in planetary air temperatures. Leaves of Artemisia tridentata, Erigeron speciosus, Festuca thurberi, Helianthella quinquinervis, Potentilla fruticosa, Potentilla gracilis and Rhodiola integrifolia were collected from plants growing in situ in control and infrared (IR)-heated (22 W m −2) plots in a meadow near the upper elevational distribution limit for A. tridentata. For six of the seven herbaceous species, RWC was not significantly different from that for A. tridentata (0.903 ± 0.019 on control plots and 0.846 ± 0.031 from heated plots). However, RWC was 0.644 ± 0.04 and 0.596 ± 0.029 for F. thurberi on control and heated plots, respectively. Water potential (ψ) varied from −1.04 MPa for A. tridentata (control plots) to −4.83 MPa for leaves of F. thurberi (heated plots); ψ for the other species ranged from −1.08 MPa ( R. integrifolia on control plots) to −2.62 MPa ( P. gracilis on heated plots). To characterize further the responses of water relations parameters to the IR heating treatment, pressure-volume isotherms were generated for A. tridentata and P. gracilis. Both species exhibited effects of the IR heating treatment on saturated osmotic potential and the relative symplastic water content. Based on changes in osmotic potential and relative water content, an increase in osmotically active solutes was exhibited for leaves collected from plants under heaters. Species-specific patterns of RWC and water potential (as well as effects on cellular water relations) may influence the ability of plant species to cope with changes in soil water content that are expected to occur with global warming for montane ecosystems in the western USA.

Changes in Water Relation Parameters in Leaves of Olive (Olea europaea L.) during Salinity Stress and Relief

Water relation parameters were calculated from analysis of 92 pressure-volume isotherms of leaves of two olive varieties, `Leccino' and `Frantoio', measured after 4 weeks of salinity stress and 4 weeks of subsequent relief either in hydroponics or soil culture. `Frantoio' was more salt-tolerant than `Leccino', but no major differences in water relation parameters emerged between the two varieties. Increasing salinity from 0 to 200 mM NaCl decreased predawn leaf water potential from –0.5 MPa to –1.3 MPa, relative water content (RWC) from 97.6% to 89%, and leaf osmotic potential (Ψπ) from –2.0 to –3.5 MPa. Relative water content at turgor loss point (RWCtlp) was decreased from 89% to 85% (soil culture) and from 86% to 80% (hydroponic culture) in 0 to 200 mM CaCl-treated plants, respectively; a lower RWCtlp was also retained during the relief from salinity. Active osmotic adjustments induced by salinity was the result of accumulation of both inorganic ions and compatible solutes (e.g., mannitol). Maintenance of lower Ψπ and RWCtlp during relief indicated that salinized plants were better adapted to withstand further stress and that this potential might be exploited to harden olive plants to be used in arid or saline environments.

Equation of state data for silicon-germanium alloys under pressures up to 42 GPa

Pressure-volume (p – v) isotherms were studied on Si-Ge alloys at room temperature under pressures up to 42GPa by energy dispersive X-ray diffraction. These data are compared with the behaviour of the pure elements and show some characteristic nonlinearities in the variations of the respective elastic parameters with respect to the alloy concentration.

Constant-pressure molecular dynamics simulations of room-temperature pressure-volume isotherms of Ne and Ar at high densities

Constant-pressure molecular dynamics techniques have been used to simulate pressure-volume isotherms of room-temperature Ne and Ar using generally adopted pair potentials. Deviations between the experimental and simulated isotherms are discussed in terms of the repulsive part of the potentials. The relevance of the simulations for the studies of Ne and Ar crystallites in metals has been considered.

Pressure Induced Change of The Nature of The Isotropic to Nematic Phase Transition for 4-(Trans-4-Butylcyclohexyl)Benzonitrile

Abstract Pressure-volume isotherms for 4-(trans-4-butylcylohexyl)benzonitrile were measured by means of piston-cylinder method. This substance has a monotropic nematic phase at atmospheric pressure. But over a pressure, the nature of isotropic to nematic phase transition changed from monotropic to enantiotropic phase transition. It is the first observation in P-V-T experiments that the monotropic isotropic-nematic transition changes enantiotropic under pressure.

Perturbed hard-sphere equations of state of real fluids. II. Effective hard-sphere diameters and residual properties

Effective hard-sphere diameters for argon, krypton and xenon have been calculated from the currently most accurate perturbation theories using accurate pair-potential models. Based on the theoretical diameters and on pressure—volumes—temperature data for the real fluids, the van der Waals parameter a p is examined and two conjectures generalizing the behavior of a p are formulated. These conjectures make it possible to evaluate the effective hard-sphere diameters of simple liquids at the triple-point temperature from data for a few low-temperature pressure—volume isotherms. This fact, together with a corresponding-states principle that emerges from results for the theoretical diameters, forms the basis of a simple method which we propose for evaluating temperature-dependent effective hard-sphere diameters of a perturbed hard-sphere equation of state, independently of any pair-potential model and any perturbation theory. The applicability of the method is demonstrated for methane and its extension to nonsimple liquids is discussed. It is also shown that the use of an approximate theory and/or approximate pair-potential model may often result in a qualitatively misleading picture of a p behavior.