Enrico Matteoli

Solute–solute interactions in water. II. An analysis through the Kirkwood–Buff integrals for 14 organic solutes

From accurate data of activities (a), partial molar volumes (V), and compressibility (K) of binary aqueous mixtures, the so‐called Kirkwood–Buff integrals Gij defined by Gij=∫∞0u2009[u2009gij(r) −1] 4πr2u2009dr=f(a,V,K), (i=1,2;u2009j=1,2), have been calculated in the whole concentration range. Fourteen water(1)‐organic cosolvent(2) systems [methanol, ethanol, 1‐propanol, 1‐butanol, 2‐methyl‐2‐propanol, acetonitrile, acetone, dimethylsulfoxide, tetrahydrofuran, piperidine, pyridine, 1,4‐dioxane, 2‐aminoethanol, 2‐(dimethylamino)ethanol] have been studied at 25u2009°C, and two (methanol and ethanol) also at different temperatures. The Gij functions show these features in relation to the molecular structures of component 2: (1) when this component presents a large nonpolar moiety, extrema are exhibited by Gij’s at certain concentrations the more marked the larger the nonpolar portion; (2) when component two is bifunctional, Gij trend is monotonic with concentration; (3) in the temperature range 0–90u2009°C, G22 increases and G12...

A simple expression for radial distribution functions of pure fluids and mixtures

A simple expression for the radial distribution function (RDF) of pure fluids and mixtures is presented. It satisfies the limiting conditions of zero density and infinite distance imposed by statistical thermodynamics. The equation contains seven adjustable parameters; they have been fitted to extensive literature data of RDF’s for a Lennard‐Jones fluid at different values of temperature and density. These in turn have been expressed as functions of reduced temperature and density, thus allowing a complete parametrization with respect to these variables using 21 parameters altogether with fairly good accuracy. The values of the reduced pressure and internal energy calculated by numerical integration of the completely parametrized equation compare fairly with literature molecular dynamics simulation results. The capability of the expression to fit to RDF’s of mixtures has been checked against some of the extensive RDF simulation data of binary mixtures of Lennard‐Jones fluids with different diameters avail...

The effect of the molecular shape on the enthalpic behaviour of liquid mixtures : cyclic hydrocarbons in heptane and tetrachloromethane

Excess enthalpies HE at 298.15 K have been determined by flow microcalorimetry for binary mixtures of heptane or tetrachloromethane + a cyclic hydrocarbon (cycloheptane, cyclooctane, cyclodecane, 1,2,3,4-tetrahydronaphthalene, cis-decahydronaphthalene, trans-decahydronaphthalene, bicyclohexyl). With the exception of tetrahydronaphthalene + tetrachloromethane and of trans-decahydronaphtalene + heptane, all mixtures examined exhibit positive deviations. HEs have been analysed in terms of the DISQUAC model. Partial molar excess enthalpies at infinite dilution as well as standard enthalpies of solvation, ΔHo, have been evaluated for cycloalkanes in the two solvents and compared with those of linear and branched alkanes. The effect of cyclization upon ΔHo has been discussed and the contributions to ΔHo of the cavity and of the interaction terms have been estimated through the scaled particle theory.

Isothermal liquid-vapour equilibria of mixtures containing organic compounds. 3. Excess Gibbs free energies of cyclohexane + a linear ether.☆

Abstract Vapour-liquid equilibria of binary mixtures of cyclohexane with a linear mono-, di-, or triether (diethyl, dipropyl, dibutyl, methyl butyl, ethyl butyl ether, formaldehyde dimethyl acetal, formaldehyde diethyl acetal, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyleneglycol dimethyl ether) were determined at 298.15 K by head-space gas cromatographic analysis of the equilibrated vapour phase. Excess molar Gibbs energies, G E , for the investigated mixtures were obtained by a least-squares treatment of the equilibrium results (x–y). The G E values are positive for all the systems and increase with increasing the ratio of oxygen to carbon atoms in the ether molecule. There is clear evidence for the effect of position of the oxygen atom in the chain structure of monoethers as well as for the effect of distance of two -0- groups in diethers. The behaviour of the activity coefficients at infinite dilution and of the free energies of solvation as well as of molar excess entropies, obtained from G E and the known excess enthalpies, are briefly discussed. The experimental G E values are compared with the predictions of a group contribution model in the random-mixing approximation.

Excess volumes of cyclohexane + a linear ether at 298.15 K

Abstract By means of a vibrating tube densimeter, the molar excess volumes, VE, at 298.15 K, have been determined in the whole mole fraction range, for binary mixtures of cyclohexane with a linear mono-, di-, or triether (diethyl, dipropyl, dibutyl, methyl butyl, ethyl butyl ethers, dimethoxymethane, diethoxymethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethylene glycol dimethyl ether). Also, the limiting partial molal volumes have been evaluated from the high dilution data. The VE values are positive for all systems and increase with increasing the number of oxygen atoms in the ether molecule. There is a clear evidence for the effect of: (i) chain lengthening; (ii) position of the -O- group in the chain structure of monoethers; (iii) distance of two -O- atoms in diethers. The Flory theory of nonpolar solutions has been applied to some of the present mixtures. The sign, the magnitude, and the trend of VE with ether structure are correctly predicted.

Calorimetric study of molecular interactions in mixtures of substances containing carbonyl groups

Abstract A Tian-Calvet type calorimeter has been used to determine molar excess enthalpies, HE, as a function of concentration at atmospheric pressure and 298.15 K for some binary liquid mixtures containing linear ketones with tetrachloromethane or benzene and linear diketones with n-heptane or cyclohexane. The experimental HE results are interpreted in terms of molecular interactions and of the “homoproximity effect”.

Concentration fluctuations in fluid mixtures. II.

The method developed in a previous paper [R. Mazo, J. Chem. Phys. 129, 154101 (2008)] for extracting information on the size of relative fluctuations in multicomponent systems is tested on ten binary systems and one ternary system. For the binary systems, it is found that the approximation works well for mole fractions in the range of 0.15-0.85 in most cases. For the ternary case, the method inherently yields less information and is valid only over a more restricted range for the case studied (chloroform-methanol-acetone). It is found that the predicted ratio of number fluctuations is approximately equal to the ratio of molar volumes of the components.

10 Mixtures of dissimilar molecules

Summary Equations (10.14) and (10.15), which are the basis of the present theory, are mathematically exact. The choice of the closure expression, Equation (10.21), relating the cross-direct-correlation integral to the other two integrals in a binary mixture allows us to solve these equations simply and analytically using only the pure-fluid thermodynamic data. It is demonstrated here that simple geometric- and arithmetic-mean closures are needed for simple model fluids. It is also demonstrated that a weighted-arithmetic-mean closure expression is sufficient to represent the relation between the cross-direct-correlation integral to the other two correlation integrals of binary mixtures. Success of this theory in its application to a variety of mixtures comprised of components with polar and associating intermolecular potential energies is indicative of its promise as a strong technique for prediction of properties of complex dissimilar mixtures of practical interest. The present theory has allowed us to perform calculations of properties and phase equilibria of mixtures. There are several points to be noted about the advantages of the present techniques compared with other existing thermodynamic calculation methods for mixtures: (i) The present theory allows us to perform thermodynamic calculations for the whole range of mixture compositions and not just at the infinite-dilution and high-concentration limits as has been the case for most of the fluctuation-theory techniques. (ii) The present theory is applicable for mixtures consisting of dissimilar species with large differences in molecular size, shape, and energetics. It is specifically useful for polar and associating molecular fluids for which, generally, no accurate intermolecular-potential-energy functions are available. (iii) With the application of the weighted-arithmetic-mean closure for the cross-direct-correlation-function integrals, Equation (10.21), it has become possible to derive analytic expressions for activity coefficients in complex mixtures consisting the dissimilar molecules. The resulting activity-coefficient expressions allow us to perform vapor-liquid and liquidliquid equilibria computations for such mixtures. The accuracy of these calculations are is good as the best available phase-equilibria computational techniques for mixtures. (iv) What makes the relations among the direct-correlation-function integrals (or fluctuation integrals) introduced here particularly interesting is the fact that only one closure relation is needed to determine all the binary-mixture properties. Detailed studies are under way in order to develop analytic expressions for total and partial molar properties of multicomponent systems using the present theory.