Estimation of the Spinodal Curve for Liquids: Application to 2,3-Dimethylbutane

Abstract

For a pure substance, the spinodal curve is defined as the locus where thermodynamic quantities such as the thermal expansion coefficient a,, the isothermal compressibility KT, and the isobaric heat capacity C, are expected to diverge. Its location is of particular importance from both practical and theoretical points of view, since it represents the limit beyond which a particular state of matter, in our case the liquid state, can exist or not. In this work, several predictions of the spinodal curve have been tested, compared, and discussed for 2,3-dimethylbutane. Thecomparison with results found in the literature reveals that some conclusions established here could be of general application.

Prediction of surface tension of liquids

“…In this sense, it has been shown [7] that Deiters' EOS [8] gives good predictions for vapor-liquid equilibrium (VLE) for a large number of substances. In addition, it has been confirmed that this EOS yields estimations of a spinodal curve compatible with results obtained from extrapolation of experimental measurements in both stable and metastable regions and those obtained from Furth's treatment [9].…”

Isobaric Thermal Expansivity for Ionic Liquids with a Common Cation as a Function of Temperature and Pressure

“…As for α p pressure dependence, it is presented in Figure at several temperatures for all studied liquids. It can be observed that α p decreases as pressure is raised at all studied temperatures and all studied liquids, which is the common behavior found for other liquids. − On the other hand, the curves at different temperatures are almost parallel over the whole pressure range, a fact which contrasts with the much more complex α p pressure dependence of common solventseven relatively simple liquids as alkanes show curve crossing at high pressure. ,− …”

“…Most of these data were reported at atmospheric pressure, although there is a considerable amount of work which reports density as a function of temperature T and pressure p over extended T , p ranges. − It was found that density of RTILs is usually between (1000 and 2000) kg·m −3 , whereas its dependencies against temperature and pressure (given by the isobaric thermal expansivity α p and isothermal compressibility κ T ) are significantly milder than those found for common organic solventsboth thermodynamic coefficients present values about a half of those of molecular liquids. In addition, some studies , point to the fact that α p of RTILs presents a negative temperature dependency, opposite to that found for usual organic solvents at moderate pressures, − although it would be desirable to have some more evidence to confirm this anomalous behavior. It is the aim of this work to contribute to the knowledge of the behavior of α p against temperature and pressure for RTILs.…”

Dependence against Temperature and Pressure of the Isobaric Thermal Expansivity of Room Temperature Ionic Liquids

“…As a consequence, research about the physical properties of these compounds has received great attention in the last few years. − Most of the effort was spent in the study of physical properties of RTILs at atmospheric pressure, although in the last few years, there have been some works devoted to characterize the behavior against p and T , of several magnitudes, with the density ρ being the most widely studied. − As a result, it was concluded that the RTILs density dependencies against T and p , given by the isobaric thermal α p expansivity and isothermal compressibility κ Τ , differ significantly from those of other solvents. These differences were observed not only in the α p and κ Τ values themselves but also in the behavior of these magnitudes against temperature and pressure: there are several works , in which a negative temperature dependency for α p over the whole pressure range is shown, where this behavior is not usually found for organic solvents at moderate pressures. − Moreover, by checking the α p literature data, − it seems to be that this is not an isolated case, but the rule for RTILs.…”