Pressure and temperature shifts of librational modes in solid benzene: the isochores and the proportionality between the thermal expansion and isothermal compressibility tensors

The behaviour of the low frequency Raman modes as a function of temperature and pressure in polycrystalline benzene has been studied. It is shown that the frequency decrease as a function of pressure is linear at high pressures and becomes nonlinear as the melting curve is approached. In our experimental range the isochrome curves corresponding to three different librational motions are superposed in the P,T diagram giving “isospectrum” paths which, in fact, are isochoric traces of the solid. It seems that at low temperatures this behaviour is no longer valid. Nevertheless it is concluded that in our experimental range the thermal expansion and the isothermal compressibility tensors are proportional and it is shown that this hypothesis is compatible with the thermodynamical and elasticity laws whatever the crystalline symmetry.     

Baric dependence of the isothermal compressibility of liquid diols and monoethanolamine

The isothermal compressibility of three terminal diols, monoethanolamine, and water is measured on a unique setup with direct compression at 298 K in a pressure range of 0.1–300 MPa. The lowest baric dependence is determined for ethylene glycol; the highest, for 1,4-butanediol. The crystallization of this diol at ～80 MPa is observed for the first time. The obtained data are discussed from the viewpoint of the stability of the hydrogen bond networks in the investigated liquids.     

On the accurate direct computation of the isothermal compressibility for normal quantum simple fluids: application to quantum hard spheres

A systematic study of the direct computation of the isothermal compressibility of normal quantum fluids is presented by analyzing the solving of the Ornstein-Zernike integral (OZ2) equation for the pair correlations between the path-integral necklace centroids. A number of issues related to the accuracy that can be achieved via this sort of procedure have been addressed, paying particular attention to the finite-N effects and to the definition of significant error bars for the estimates of isothermal compressibilities. Extensive path-integral Monte Carlo computations for the quantum hard-sphere fluid (QHS) have been performed in the (N, V, T) ensemble under temperature and density conditions for which dispersion effects dominate the quantum behavior. These computations have served to obtain the centroid correlations, which have been processed further via the numerical solving of the OZ2 equation. To do so, Baxter-Dixon-Hutchinson's variational procedure, complemented with Baumketner-Hiwatari's grand-canonical corrections, has been used. The virial equation of state has also been obtained and several comparisons between different versions of the QHS equation of state have been made. The results show the reliability of the procedure based on isothermal compressibilities discussed herein, which can then be regarded as a useful and quick means of obtaining the equation of state for fluids under quantum conditions involving strong repulsive interactions.     

Density and isothermal compressibility for two trialkylimidazolium-based ionic liquids at temperatures from (278 to 398) K and up to 120 MPa

In this paper, a densimeter based on vibrating tube principle is used to determine experimentally the density of 1-butyl-2,3-dimethylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide at temperatures between (278.15 and 398.15) K and at pressures up to 120 MPa. The apparatus was calibrated by using water, vacuum and bromobenzene. The Tammann–Tait equation of state was used to correlate (p, T, ρ) results with standard deviations around 2 · 10⁻⁴ g · cm⁻³. Other volumetric properties, such as isothermal compressibility and isobaric thermal expansivity, were obtained from this equation. For each ionic liquid, the α_p isotherms present a crossing point within the experimental pressure range. Besides, the effect that the C2-methylation in the imidazolium cation provokes on density values is analyzed. The prediction ability of the group contribution methods of Gardas and Coutinho and Jacquemin et al. were tested with the experimental densities.     

Densities,excess molar volume,isothermal compressibility,and isobaric expansivity of (dimethyl carbonate + n-hexane) systems at temperatures (293.15 to 313.15) K and pressures from 0.1 MPa up to 40 MPa

The densities of dimethyl carbonate, n-hexane and their mixtures were measured for 12 compositions at five different temperatures varying from (293.15 to 313.15) K and over the pressure range of (0.1 to 40) MPa. The densities of pure substances and their mixtures at atmospheric pressure were measured by a vibrating-tube densimeter. The densities at high pressures were measured by a variable-volume autoclave and precise analytical balance. The excess molar volume, isothermal compressibility, and isobaric expansivity were derived from the experimental densities.     

Isothermal compressibility and correlation radius near the critical point: Numerical analysis of the Ornstein-Zernike equation

Solution of the Ornstein-Zernike equation is analyzed numerically in the Percus-Yevick and hyperchain approximations for a system of Lennard-Jones particles in a critical region. The temperature dependences of correlation functions, isothermal compressibility η, and correlation radius of density fluctuations ζ are investigated at a critical density; the corresponding critical indices are determined. It is shown that the Percus-Yevick approximation yields satisfactory results when the correlation functions are calculated within a range corresponding to approximately 50 atomic (molecular) diameters. In this case, with ≈5% deviations from the critical temperature, the calculated and experimental values of η and critical indices are in good agreement. Tver State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 5, pp. 799–807, September–October, 1995. Translated by I. Izvekova     

Pressure and volume dependence of thermal conductivity and isothermal bulk modulus up to 1 GPa for poly(isobutylene)

The thermal conductivity λ and heat capacity per unit volume ρc_p of poly(isobutylene)s, one 2.8 in weight average molecular weight and one 85 kg mol⁻¹ in viscosity average molecular weight (PIB-2800 and PIB-85000), have been measured in the temperature range 170–450 K at pressures up to 2 GPa using the transient hot-wire method. At 297 K and atmospheric pressure, λ = 0.115 W m⁻¹ K⁻¹ for PIB-2800 and λ = 0.120 W m⁻¹ K⁻¹ for PIB-85000. The bulk modulus B_T has been measured in the temperature range 170–297 K up to 1 GPa. At atmospheric pressure, the room temperature bulk moduli B_T are 2.0 GPa for PIB-2800 and 2.5 GPa for PIB-85000 with dB_T/dp = 10 for both. These data were used to calculate the volume dependence of λ, At room temperature and atmospheric pressure (liquid phase) we find g = 3.4 for PIB-2800 and g = 3.9 for PIB-85000, but g depends strongly on temperature for both molecular weights. The difference in g between the glassy state and liquid phase is small and just outside the inaccuracy of g of about 8%. The best predictions for g are given by the theoretical model of Horrocks and McLaughlin. We have found that PIB exhibits two relaxations, where one is associated with the glass transition. The value for dT_g/dp at atmospheric pressure (for the main glass transition) is about 0.21 K MPa⁻¹ for both molecular weights. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1781–1792, 1998     

Correlation of the prigogine-flory theory with isothermal compressibility data. I. Systems with quasi-spherical molecules

The isothermal compressibilities K_T for cyclohexane + benzene, cyclohexane + toluene and benzene + toluene systems at 25, 35, 45 and 60°C have been used to test the Prigogine-Flory theory using Van der Waals and Lennard-Jones energy potentials. Flory's energy parameter X ₁₂ was calculated for these systems at the four temperatures. From X ₁₂ for the equimolar mixture, the following excess functions were calculated: (?V^E/?_p)_T which is related to K _T ^E , the heat of mixing H ^E , and the excess volume V ^E . The theory and any of the two potentials give (?V^E/?_p)_T which fit the experimental data, but H ^E and V ^E , calculated using the same X ₁₂ parameter, depart appreciably from the experimental data even though they agree in sign and have the essential features of the excess functions. The departure is apparent in both magnitude (in particular for the cyclohexane + benzene, and cyclohexane + toluene systems) and in the temperature dependence. The conclusion is that the X ₁₂ parameter does not predict the thermodynamic properties of these systems and the Lennard-Jones potential, involving a more complicated expression, does not contribute any improvement over the Van der Waals potential.     

Correlation of the Prigogine-Flory theory with isothermal compressibility and excess enthalpy data for cyclohexane + alkane mixtures

The Prigogine-Flory theory is applied to isothermal compressibilities, at 25, 35, 45 and 60°C and to heats of mixing at 25°C for cyclohexane + n-alkane systems. To this purpose, the van der Waals and the Lennard-Jones potentials have been adopted. The energy parameter ₁₂ has been calculated from the experimental data, and its dependence on the n-alkane number of carbons has been studied. Taking the ₁₂ value obtained for the equimolecular mixture, the excess functi¹/ns (V^E/P)_T, H^E and V^E have been calculated and the results compared with experimental values.     

Correlation of the prigogine-flory theory with isothermal compressibility and excess enthalpy data for benzene +n-alkane mixtures

Isothermal compressibilitiesκ _T for benzene + n-alkane systems at 25, 35, 45, and 60°C have been used to check the Prigogine-Flory theory using the van der Waals and Lennard-Jones potentials in order to study the energy-volume dependence. The Flory interaction parameter χ₁₂ has also been calculated for those set of systems at four temperatures. The variation of χ₁₂ with the number of carbon atoms in the n-alkane was studied. Three excess functions have been obtained from χ₁₂ for the equimolecular mixture: (?V ^E/?p)_T which is related toκ _T ^E , the excess enthalpy H ^E , and the excess volume V ^E . Except for H ^E theoretical predictions using a Lennard-Jones potential are in good agreement with the experimental data. A similar treatment has been performed for the same set of systems but using H ^E data at 25°C. The theory, using a van der Waals potential, predicts correctly the variation of the three excess functions with the chain length of the n-alkane but using a Lennard-Jones potential results in better agreement for the order in the magnitude of these excess functions.     

Densities,excess volumes,isobaric expansivity,and isothermal compressibility of the (1-ethyl-3-methylimidazolium ethylsulfate + methanol) system at temperatures (283.15 to 333.15) K and pressures from (0.1 to 35) MPa

Densities of pure 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid – [C₂mim][EtSO₄] and its mixtures with methanol have been measured with an accuracy of ±0.2 kg · m^?3, over the temperature range (283.15 to 333.15) K and pressure range (0.1 to 35) MPa, using a vibrating tube densimeter. Excess volumes have been calculated directly from the experimental densities. The latter data have been correlated by the Tait equation with the temperature dependent parameters for the pure ionic liquid and by a van Laar-type equation, involving parameters dependent on temperature and pressure for the mixtures. The isobaric expansivity, isothermal compressibility, and related excess properties have been calculated. The exceptionally strong influence of pressure and temperature on these properties has been observed.     

Dissolved states of ionene polymers in water-acetone and their relation to the ionic partial molar adiabatic compressibility and volume

Solution properties of water-soluble synthetic polymer, 3,3-ionene and 6,6-ionene chloride and bromide disolved in water-acetone mixtures up to acetone content 50 wt% were investigated. Their partial molar volumes V ₂ ^o and partial molar adiabatic compressibilities K _s ^o were determined. Ionic additivity of V ₂ ^o with respect to the cation of backbone polymer chain and the counter-anion was confirmed quantitatively. The ionic additivity of V ₂ ^o is discussed along with the K _s ^o in their relation to the counterion binding of ionene polymers. Effects of ionic sites on the ionene are strong but they don't break the solvation layer.     

Effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate)

The effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate) (PET) have been investigated. The Instron capillary rheometer was adapted as a high-pressure dilatometer to perform experiments up to 40,000 psi. Compressibilities of solid and molten PET were measured. The increases in compressibility with increase in temperature for the solid state are discussed in terms of free-volume theory. Results obtained for the melt are explained by invoking the second law of thermodynamics and the effect of pressure on the Gibbs free energy. The effects of temperature and compression rate on the pressure of crystallization (P_c) were also studied. As the crystallization temperature was increased from 240 to 286°C, P_c increased by about 16,000 psi. As the compression rate was raised from 1%/min to 8%/min, P_c increased 10,000 psi. At some undetermined compression rate above 8%/min it seemed impossible to induce crystallization in the melt, even with pressures up to 40,000 psi. Analysis of data on the kinetics of crystallization of PET melt under high pressures revealed low Avrami exponents, for which no unequivocal explanation is offered. It is possible, however, that crystallization at high pressure promotes the formation of a morphology made up of a certain percentage of “extended chains.” The alteration in the attendant spatial geometry involved in the crystallization might explain the lower Avrami exponents found. In another set of experiments, crystallization temperatures (T_c) were measured by slowly cooling PET melt under high pressures. As the pressure was raised from 3000 to 15,000 psi, T_c increased from about 246 to 282.5°C. These results are consistent with thermodynamic theory.     

Volumetric and compressibility studies for (L-arginine + D-maltose monohydrate + water) system in the temperature range of (298.15 to 308.15) K

The density and speed of sound of L-arginine (0.025–0.2 mol kg^?1) in aqueous + D-maltose (0–6 mass% of maltose in water) were obtained at temperatures of (298.15, 303.15 and 308.15) K. The apparent molar volume, limiting apparent molar volume, transfer volume, as well as apparent molar compressibility, limiting apparent molar compressibility, transfer compressibility, pair and triple interaction coefficients, partial molar expansibilities, coefficient of thermal expansion and also the hydration number, were calculated using the experimental density and speed of sound values. The results have been discussed in terms of solute–solute and solute–solvent interactions in these systems. Solute–solvent (hydrophilic–ionic group and hydrophilic–hydrophilic group) interactions were found to be dominating over solute–solute (hydrophobic–hydrophilic group) interactions in the solution, which increases with increase in maltose concentration.     

Pullulan reduces the non-specific amplification of loop-mediated isothermal amplification (LAMP)

Loop-mediated isothermal amplification (LAMP) has been developed as a versatile method for nucleic acid analysis in many applications. However, non-specific LAMP leading to false-positive outcomes has been observed frequently. To solve this problem, we selected six molecules as the additives for evaluating their effects on the improvement of the LAMP specificity. Experimental results show that bovine serum albumin (BSA) and DL-dithiothreitol (DTT) have negative effects on the LAMP specificity; dimethyl sulfoxide (DMSO), tetramethylene sulfoxide (TMSO), and glycerol could inhibit the non-specific LAMP moderately. Surprisingly, pullulan shows an ability to inhibit the non-specific amplification of LAMP significantly without affecting the sample amplification of LAMP, and this inhibitory effect is concentration dependent. Thus, pullulan could be considered as the most promising additive to improve the amplification specificity in the LAMP-based detection and analysis of nucleic acids.