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Raman spectra of methanol-water mixtures were measured over the whole composition range at room conditions. The spectra are used to quantify the strength of intermolecular interactions in terms of local internal pressures. The conclusions derived from the spectroscopic analysis are discussed within the framework of the solvation pressure model using values of the cohesion energy density expected in the mixture. This work demonstrates that an appropriate analysis of Raman spectroscopy experiments can be used to quantify the local internal pressures due to intermolecular interactions in liquid mixtures, provided that high pressure results of the pure liquids are available.

We have carried out a systematic study of abiotic precipitation at different temperatures of several Mg and Ca carbonates (calcite, nesquehonite, hydrocalcite) present in carbonaceous chondrites. This study highlights the capability of Raman spectroscopy as a primary tool for performing full mineralogical analysis. The precipitation reaction and the structure of the resulting carbonates were monitored and identified with Raman spectroscopy. Raman spectroscopy enabled us to confirm that the precipitation reaction is very fast (minutes) when Ca(II) is present in the solution, whereas for Mg(II) such reactions developed at rather slow rates (weeks). We also observed that both the composition and the reaction mechanisms depended on temperature, which might help to clarify several issues in the fields of planetology and geology, because of the environmental implications of these carbonates on both terrestrial and extraterrestrial objects.

Raman spectra of 1,2-ethylenediamine (EDA) in aqueous solutions are used to demonstrate that EDA molecules experience an anti–gauche conformational change resulting from the interactions with water. The observed Raman shift reveals a compressive (hydrophobic) effect of water on both methylene and amino groups of EDA. Raman spectra of EDA at high pressures are used as reference to quantify the intermolecular EDA–H2O interactions in terms of local pressures. These results are compared with macroscopic solvation pressures calculated from the cohesive energy parameter. We compare and discuss all our observations with available computational and experimental studies.

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.

Measurements of the refractive index from 293 to 321 K at four fixed wavelengths, from 587.6 to 404.7 nm, are reported for valeric acid (pentanoic acid), caproic acid (hexanoic acid), oenantic acid (heptanoic acid), caprylic acid (octanoic acid), and pelargonic acid (nonanoic acid). We also report the temperature and wavelength dependencies of the refractive index obtained from a least-squares routine. The agreement between the measured and calculated refractive indices lies within the experimental uncertainty.

Measurements of the refractive index from 288 to 318 K at five fixed wavelengths, from 656.3 to 404.7 nm, are reported for benzene, toluene (methylbenzene), o-xylene (1,2-dimethylbenzene), m-xylene (1,3-dimethylbenzene), and p-xylene (1,4-dimethylbenzene). We also report the temperature and wavelength dependencies of the refractive index obtained from a least-squares routine. The agreement between the measured and calculated refractive indices lies within the experimental uncertainty.

The enthalpies of dilution for aqueous solutions of [Co(en)3]Br3, [Co(pn)3]Cl3, and [Co(tn)3]Cl3 (where en = 1,2-diaminoethane, pn = 1,2-diaminopropane, and tn = 1,3-diaminopropane) have been measured at 25°C, and up to m = 1 mol-kg−1, using an isoperibol calorimeter by the “long-jump” method. Relative apparent molar enthalpies Lφ have been extracted as an empirical equation relating Lφ and m. Previously reported experimental data and theoretical predictions in the restricted primitive model (RPM) for 3:1 and 1:3 aqueous electrolytes are shown together with the new experimental material.

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.

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.

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

Osmotic coefficients of aqueous solutions of tris(ethylenediamine)cobalt(III) chloride, tris(ethylenediamine)cobalt(III) bromide, tris(ethylenediamine)cobalt(III) iodide, tris(ethylenediamine)cobalt(III) nitrate, and tris(ethylenediamine)cobalt(III) perchlorate have been measured from 0.000 to 0.025 mol-kg −1 . The freezing-point method was used for the determination of the osmotic coefficients. These results were fitted to semiempirical least-squares equations, and these equations were used to calculate the mean molal activity coefficients

Brillouin spectra obtained in dynamic light-scattering experiments are reported for the three isomeric xylenes (ortho-, meta-, and paradimethylbenzenes) between 288 and 363 K. Limiting sound velocities and relaxation times, as obtained from the polarized spectra using the theory developed by Mountain [J. Res. Natl. Bur. Stand. 70A, 207 (1966)], reveal the existence of a relaxation process. Our results suggest that the relaxation process in liquid xylenes has a purely vibrational nature. Vibrational-translational energy exchanges in xylenes are analyzed in terms of available molecular models and compared to those previously obtained for toluene and benzene. The results presented here confirm the important role played by the molecular geometry in the vibrational relaxation process, as the relative arrangement of the methyl groups has significant effect in determining the relaxing vibrational modes.

The enthalpies of dilution of aqueous solutions of {Co(en)3}Cl3and {Co(tn)3}Cl3(where en = 1,2-diaminoethane andtn = 1,3-diaminopropane) have been measured up to m = 1 mol · kg − 1at T = 278.15 K and atmospheric pressure with an isoperibol calorimeter by the long-jump method. Relative apparent molar enthalpies Lφ,mhave been extracted from an empirical polynomial of the molality square root. Previously reported data at T = 298.15 K are compared with the new experimental dilution results. A noticeable decrease in Lφ,mwas observed at every experimental concentration when temperature diminished from 298.15 K to 278.15 K. An inversion in the relative layout for the Lφ,mcurves of aqueous {Co(en)3}Cl3and {Co(tn)3}Cl3was also found., This research was supported by DGESIC (M.E.C., Spain) under Research ProjectNo.: PB98-0832.

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.

Excess heat capacities, CEp have been obtained through the concentration range at 25°C for five sets of systems of type An + B: hexafluorobenzene + 2,2,4-trimethylpentanc and 2,2,4,4,6,8,8-heptamethylnonane; hexafluorobenzene + cyclohexane (10° W) and dicyclohexyl (W); 1-chloronaphthalene + 2,2-dimethylbutane, 2,2,4-trimethylpentane (W) and 2,2,4,4,6,8,8-heptamethylncnane (W), 1-chloronaphthalene + n-hexadecane; 1-chloronaphthalene + cyclohexane and dicyclohexyl (15°, W). For the systems indicated, CEp has a W-shape, i.e., two minima separated by a maximum or two changes of sign of the curvature. The W-shape does not occur for hexafluorobenzene + cyclohexane at 25° but appears at 10°. Temperature and molecular size act on CEp through the degree of solution non-randomness as indicated by GE and the concentration-concentration correlation function, Scc which is a good predictor for the W-shape and of the concentration at which the maximum appears. The W-shape corresponds to an Scc value greater than 0.7 and GE > 800 J mol−1, the temperature being within 100 K of the UCST.

Apparent heat capacities have been measured for fifteen branched and cyclic alcohols in dilute n-decane solution at 25 °C. The alcohols were 2-methyl-2-propanol, cyclohexanol, 3-methyl-3-pentanol, trans-, cis-, and mixed isomer 2-methylcyclohexanol, 1-methylcyclohexanol, 3-ethyl-3-pentanol, cyclooctanol, 3,7-dimethyl-1-octanol, 5-decanol, 4-propyl-4-heptanol, cyclododecanol, 5-butyl-5-nonanol, and 8-hexadecanol (in n-hexane). Excess heat capacities CpE throughout the concentration range were measured at 25 °C for: 1-hexanol + n-hexadecane (n-C16) and + 2,2,4,4,6,8,8-heptamethylnonane (br-C16), 4-propyl-4-heptanol, and 1-decanol + n-decane, 3-methyl-3-pentanol + n-C16 and + br-C16 and at 27 °C for cyclohexanol + n-C16 and + br-C16. Also, for 3-methyl-3-pentanol + n-decane CpE was measured at 10, 25, 40, and 50 °C. For a series of isomeric alcohols, the apparent molar heat capacities show a maximum against concentration which decreases and moves to higher alcohol concentration as the hydroxyl group on the alcohol becomes increasingly hindered, effectively reducing the alcohol self-association capabilities. This situation is also reflected by the heat capacities of the pure alcohols which increase strongly in magnitude in going from a linear 1-alcohol to an isomeric alcohol which has its hydroxyl group on a quaternary carbon atom. CpE of the mixtures are negative at low alcohol concentrations turning positive at increasingly higher alcohol concentrations as the steric hindrance on the hydroxyl group increases. Throughout most of the concentration range CpE for the branched or cyclic alcohols is considerably more positive than for the corresponding isomeric 1 -alcohol. For the highly hindered 3-methyl-3-pentanol CpE(T) passes through a maximum. All of the above behaviour is explained by the Treszczanowicz–Kehiaian model for self-associated liquids + inert solvents which has been applied to the present data. Equilibrium constants have been obtained for alcohol association and are sensitive to alcohol structure. At low alcohol concentrations, while for the linear 1-alcohols tetramers are the predominant species and dimer are almost absent, for the corresponding isomeric alcohols the concentration of tetramers is severely reduced and the lower species, i.e. trimers and dimers, are more important. For the highly hindered alcohols, monomers are the predominant species in dilute solution reflecting the decrease in self-association ability that steric hindrance of the hydroxyl group imposes on them.

Solutions containing both poly(4-vinylpyridine) (P4VP) and poly(acrylic acid) (PAA) in 50% v/v metanol-water have been studied at room temperature by means of fluorescence studies, spectrophotometry and potentiometry. The results show the formation of a polycomplex between the polymers. Its stoichiometry is 0.5–0.6 PAA:1 P4VP and only slightly depends on polymer concentration for a range of very dilute solutions (10−3–10−4 M in monomeric units). The polycomplex is largely stabilized through hydrogen bonds but there is some proton transfer and the resulting coulombic interactions also contribute to the stabilization. The role of hydrophobic interactions is also discussed.

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.

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.

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.