Mateo Díaz Peña

Range of simple scaling and critical amplitudes near a LCST. The 2-butoxyethanol + water system

Abstract The closed-loop coexistence curve of 2-butoxyethanol + water has been determined with special attention to the region near the LCST. The results have been analyzed in terms of extended scaling equations. The range of validity of simple scaling has been determined, and found to be similar to that of other binary systems with UCST. The first correction-to-scaling amplitude has been found to be negative, in agreement with numerical solutions of three-dimensional Ising models, and in contradiction with the results of the field theoretical models proposed so far. Using a decorated lattice model, the order parameter can be described very accurately at temperatures where the simple scaling is no longer valid. The diameter of the coexistence curve has been found to show a (1 - α) anomaly when the weight fraction is used as composition variable.

Liquid–liquid critical phenomena. The influence of pressure on the coexistence curve of the methanol + cyclohexane system

The liquid–liquid coexistence curve of methanol + cyclohexane has been measured in the range 0.1≤P/MPa≤13.0. The difference in mole fraction between both branches of the coexistence curve has been found to be a more convenient order parameter than the volume fraction difference. The diameter of the coexistence curve has been found to show no anomaly within the experimental uncertainty. The pressure dependence of the correction to simple scaling terms are mostly masked by their estimated uncertainties. Reliable values for xc and Tc have been determined, being xc invariant with pressure within the experimental uncertainty. The data have been found to be compatible with the two‐scale‐factor universality hypothesis.

Order effects in the excess thermodynamic properties of benzene + alkane mixtures

Mixtures of benzene and an alkane have been analysed using the method of Patterson. Order contributions in pure benzene, pure n-alkane and benzene + n-alkane mixtures and sterichindrance effects in some benzene + branched-alkane mixtures are able to explain qualitatively the excess thermodynamic properties of these systems. Order contributions are studied in terms of the model of Heintz and Lichtenthaler. It is shown how the value of X12 obtained from HE data may be predicted from the value of X12 obtained from GE data for a system without order contributions.

Thermodynamics of methylcyclohexane + toluene and methylcyclohexane + cyclohexane mixtures from isothermal compressibility data

Measurements of isothermal compressibility, κT, have been carried out for methylcyclohexane + toluene mixtures at 298.15, 318.15, 318.15 and 333.15 K. The results were combined with data for other parameters to obtain isentropic compressibilities and heat capacities at constant volume. The corresponding excess functions κET, κEs and CEv have also been calculated and their behaviour as a function of the mole fraction and temperature studied. The Prigogine-Flory theory of mixtures, using two different potentials, has been checked from our isothermal compressibility measurements.

The unusual coexistence curve of 2-butanol + water. An experimental and theoretical study

Abstract The coexistence curve of the 2-butanol + water system has been measured at P ≈ 1 bar, with a higher precision and a more detailed description of the pinch-off region than in previous experimental studies. The data points in the vicinity of the UCST have been fitted to a simple scaling expression to obtain the critical point coordinates and an estimation of the range of validity of simple scaling. The experimental binodal has been used to test two Ising-like models including directional interactions: an asymmetric decorated lattice one and a lattice-gas model with fluctuating orientational degrees of freedom. Both models offered comparable results when a symmetrized composition variable was used.

Thermodynamics of fluorocarbon–hydrocarbon mixtures. The systems formed by 2,2,4-trimethylpentane with hexafluorobenzene and with hexafluorobenzene–benzene

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.

Volumetric properties of mixtures of simple molecular fluids

The excess volumes, VE, of several binary mixtures of simple molecular fluids have been measured as a function of composition and temperature. The results cannot be explained qualitatively using perturbation theories based on mixtures of spherical molecules and multipoles. The interplay of different kinds of anisotropy in the intermolecular potential seems to display complicated behaviour. A generalized van der Waals equation, a model based on a lattice with holes and a semiempirical equation of state have been used for fitting the experimental results satisfactorily. However, none of the models manages to predict other excess functions even for these relatively simple fluids.

Thermodynamics of mixtures with a hexane isomer. Excess volumes of 1-chlorohexane with a hexane isomer at 298.15 K

The excess volumes of 1-chlorohexane with a each of five hexane isomers have been measured at 298.15 K using a vibrating-tube densimeter. The results have been correlated using several generalized van der Waals models, including random and non-random distribution of the molecules, as well as lattice-with-holes models. None of the models is clearly superior to the other, and all of them give very poor predictions of non-fit excess properties for systems of an alkane with a hexane isomer.

Thermodynamics of three toluene-containing mixtures. Generalized van der Waals and Ising-like models

Isothermal vapour–liquid equilibrium of toluene–n-heptane, toluene–cyclohexane, and toluene–o-xylene at 348.15 K have been obtained by a dynamic method. The thermodynamic consistency of the p-T-x-y data has been tested using a Pade approximant to describe the composition dependence of the excess Gibbs energy. The results have been used to check the fitting and prediction abilities of several generalized van der Waals models, as well as an Ising-like model. None of the studied models are able to predict correctly GE, HE and VE at 298.15 K.