Enriqueta R. López

Density scaling of the transport properties of molecular and ionic liquids

Casalini and Roland [Phys. Rev. E 69, 062501 (2004); J. Non-Cryst. Solids 353, 3936 (2007)] and other authors have found that both the dielectric relaxation times and the viscosity, η, of liquids can be expressed solely as functions of the group (TV (γ)), where T is the temperature, V is the molar volume, and γ a state-independent scaling exponent. Here we report scaling exponents γ, for the viscosities of 46 compounds, including 11 ionic liquids. A generalization of this thermodynamic scaling to other transport properties, namely, the self-diffusion coefficients for ionic and molecular liquids and the electrical conductivity for ionic liquids is examined. Scaling exponents, γ, for the electrical conductivities of six ionic liquids for which viscosity data are available, are found to be quite close to those obtained from viscosities. Using the scaling exponents obtained from viscosities it was possible to correlate molar conductivity over broad ranges of temperature and pressure. However, application of the same procedures to the self-diffusion coefficients, D, of six ionic and 13 molecular liquids leads to superpositioning of poorer quality, as the scaling yields different exponents from those obtained with viscosities and, in the case of the ionic liquids, slightly different values for the anion and the cation. This situation can be improved by using the ratio (D∕T), consistent with the Stokes-Einstein relation, yielding γ values closer to those of viscosity.

Ionic Liquids Based on Phosphonium Cations As Neat Lubricants or Lubricant Additives for a Steel/Steel Contact

After doing several miscibility essays with eight ionic liquids (ILs) and four base oils, the ILs tri(butyl)ethylphosphonium diethylphosphate [P4,4,4,2][C2C2PO4] and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P6,6,6,14][(C2F5)3PF3] were selected to be studied as lubricant additives. The neat IL [P4,4,4,2][C2C2PO4], the base oils, and several blends were characterized in terms of density, viscosity, and thermal stability. The tribological performance of the miscible base oil/IL blends (1 wt %) and the neat [P4,4,4,2][C2C2PO4] were evaluated for the lubrication of an AISI 420 steel-100Cr6 steel contact pair. The friction coefficients and wear volumes obtained are also compared with those corresponding to the pure base oils and their mixtures with conventional additive zinc dialkyldithiophosphate (ZDDP). As neat lubricants, [P4,4,4,2][C2C2PO4] showed the best antifriction ability, whereas in terms of wear, better results were obtained with [P6,6,6,14][(C2F5)3PF3]. However, higher improvements in both friction and wear were found for blends containing [P4,4,4,2][C2C2PO4]. XPS analyses of the worn surfaces lubricated with these mixtures indicated the presence of phosphorus in the tribofilm formed on the wear track. However, this compound was slightly detected on tribosamples lubricated with blends containing [P6,6,6,14][(C2F5)3PF3].

pρT measurements of polyethylene glycol dimethylethers between 278.15 and 328.15 K at pressures to 12 MPa

In this paper we present a new experimental apparatus designed to measure pressure–density–temperature (pρT ) properties with a high-pressure vibrating tube densimeter. Data reliability has been verified by comparing our experimental results for methanol, n-heptane, toluene, and HFC-134a with literature data. In this work we also report new experimental densities from 278.15 to 328.15 K, and up to 12 MPa, of triethylene glycol dimethylether (TrEGDME) and tetraethylene glycol dimethylether (TEGDME). The isobaric thermal expansion coefficients, isothermal compressibility, and internal pressure have been calculated. The dependence of these properties on the length of polyethylene glycol dimethylether, CH3O–((CH2)2O)n–CH3, is analyzed.

Experimental excess volumes of organic carbonate+alkane systems. Estimation of the parameters of the Nitta–Chao model for this kind of binary mixture

Excess volumes at 298.15 K and atmospheric pressure of some organic carbonate+alkane binary systems have been measured using an Anton Paar 602 HP densimeter. For the first time, published data on excess enthalpies, excess volumes, excess Gibbs energies of the above-mentioned binary systems together with the vaporisation enthalpies and the molar volumes of the pure organic carbonates, were used to estimate the interaction parameters between the carbonate group O–CO–O and the methyl and methylene groups, CH3, CH2, respectively. The mean deviations between experimental and theoretical values were smaller than 6% for all the properties. We have also compared our results with those obtained by Garcia etal. with the Original, Tassios etal., Larsen etal. and Gmehling etal. versions of the UNIFAC model and with those obtained by Kehiaian etal. using the DISQUAC model.

Volumetric behaviour of the environmentally compatible lubricants pentaerythritol tetraheptanoate and pentaerythritol tetranonanoate at high pressures

Knowledge of proper lubricant selection and its handling can substantially influence the reliability of a refrigeration system. In this sense the awareness of several thermophysical properties of refrigerants, lubricants, and their mixtures under different conditions of pressure and temperature is highly important for designing refrigeration systems. Polyol ester oils have been proposed as lubricant candidates for refrigeration systems. In this work, we have studied the density of two polyol esters, pentaerythritol tetraheptanoate and pentaerythritol tetranonanoate, in the range 278.15 ≤ T/K ≤ 353.15 and 0.1 ≤ p/MPa ≤ 45. In addition, the behaviour of two other essential volumetric properties, namely the thermal expansion coefficient and the isothermal compressibility coefficient, as well as the internal pressure have been analysed.

Compressibilities and viscosities of reference and vegetable oils for their use as hydraulic fluids and lubricants

The use of biodegradable lubricants based on vegetable oils is receiving increasing attention, being an important area of research, in order to promote products with a reduced environmental impact during their entire life cycle. Compressibility is one of the key properties that should be taken into account to develop efficient hydraulic fluids and gear oils. The isothermal compressibility of four reference fluids, a sunflower base oil and a biodegradable oil up to 50 MPa and from 298.15 K to 373.15 K has been determined. For this aim an experimental device based on a vibrating-tube densimeter was used to obtain the density values. The density values at atmospheric pressure were correlated within an absolute average deviation of 0.07% with the Rackett equation whereas a modified Tait equation was used to correlate the experimental data over all temperatures and at higher pressures. The sunflower base oil analyzed in this work has a slightly lower compressibility than those of the reference oils for hydraulic and two stroke engines applications. Moreover, viscosities from 278.15 K to 373.15 K and the viscosity index (VI) were determined for all the analyzed oils using a SVM 3000 Anton Paar rotational Stabinger viscometer.

Experimental and predicted excess enthalpies of the working pairs (methanol or trifluoroethanol + polyglycol ethers) for absorption cycles

In this work we report the excess molar enthalpies at 298.15 K and atmospheric pressure of the mixtures 2,2,2-trifluoroethanol (TFE)+poly(ethylene glycol) dimethyl ether 250 (PEGDME 250), methanol + tetraethylene glycol dimethyl ether (TEGDME) and methanol + PEGDME 250. In the case of mixtures with methanol, the UNIFAC and DISQUAC group contribution models have been used to compare the predicted and experimental results. We have used three versions of the UNIFAC model due to Tassios et al., Larsen et al. and Gmehling et al., for which three group assignments were made. The best predictions were found with the Gmehling version of the UNIFAC model.

Experimental and predicted excess enthalpies of the 2,2,2-trifluoroethanol–water–tetraethylene glycol dimethyl ether ternary system using binary mixing data

Excess enthalpies of the ternary mixture 2,2,2-trifluoroethanol–water–tetraethylene glycol dimethyl ether and the corresponding binary mixtures at 298.15 K have been measured using a standard Calvet microcalorimeter. Wilson, NRTL, UNIQUAC and Wang et al. models have been used to correlate the binary excess enthalpies and, using the parameters obtained, to predict ternary excess molar enthalpies, HE. Several empirical equations predicting ternary-mixture properties from the binary-mixing data have been also examined.

Analysis of the intramolecular proximity effect on dichloroalkane + alkane mixtures using Nitta-Chao model

Abstract Literature data for vapor liquid equilibria, activity coefficients at infinite dilution, enthalpies of mixing, volumes of mixing of α,ω-dichloroalkane (ClCH 2 (CH 2 ) m−2 CH 2 Cl, from m=1 to 6) + − alkane mixtures together with vaporization enthalpies and molar volumes of pure dichloroalkanes were examined on the basis of the Nitta-Chao model. In this paper structure-dependent interaction energetic coefficients for this model were presented for a first time. According to the proximity effect when the two chloro groups of the chloroalkane are more separated they become independent and the reported values of the energetic parameters approach to these of the 1-chloroalkane. Similar trends were reported previously for several authors in the framework of the DISQUAC model. A comparison with the predictions of DISQUAC and UNIFAC (version of Larsen et al.) is presented.

Estimation of parameters of Nitta-Chao model for linear monoether + 1-alkanol mixtures

We have estimated the interaction parameters for ether and hydroxyl groups using an extensive experimental database of vapour-liquid equilibria, activity coefficients at infinite dilution, enthalpies of mixing and volumes of mixing of linear monoether + 1-alkanol binary systems. The theoretical results obtained with the parameters proposed are significantly closer to the experimental values than those determined with the parameters of Eckart et al. In addition, the values of thermodynamic properties obtained by the Nitta-Chao model with both set of parameters have been compared with the predictions resulting from other models, such as the DISQUAC model and the UNIFAC model, in its original version and those of Dang and Tassios, Larsen et al. (UNIFAC-Lingby) and Gmehling et al. (UNIFAC-Dortmund).