Liquid-liquid criticality in TIP4P/2005 and three-state models of water

Molecular dynamics simulations leading to the isothermal compressibility, the isobaric thermal expansivity, and the isobaric heat capacity of TIP4P/2005 water are found to be consistent with the coordinates of its second, liquid–liquid critical point reported recently by Debenedetti et al. [ Science 2020, 369, 289−292]. In accord with the theory of critical phenomena, we encounter that the rise in the magnitude of these response functions as temperature is lowered is especially marked along the critical isochore. Furthermore, response-function ratios provide a test for thermodynamic consistency at the critical point and manifest nonuniversal features sharply distinguishing liquid–liquid from standard gas–liquid criticality. The whole pattern of behavior revealed by simulations is qualitatively the same as the one of a three-state Ising model of water exhibiting a low-temperature liquid–liquid critical point. Exact solutions for the two-state components of such a three-state model are also provided.Agencia Estatal de Investigación | Ref. PID2020-115722GB-C22Universidade de Vigo/CISU

Effect of hydrophobic phenomena over the volumetric behavior of aqueous ionic liquid solutions

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGTo explore the effect of ionic liquid hydrophobicity over the volumetric properties, density has been determined for six of these compounds in aqueous solution in the temperature interval (293.15–308.15) K, covering the diluted region. For three of these binary systems, density at 298.15 K in the pressure interval (0.1–95) MPa has been also measured. The atmospheric pressure density is used together with high pressure data to calculate excess volumes as a function of pressure with high accuracy through an integration scheme based on the excess volume derivative against pressure. Since hydrophobic phenomena is known to have a greater effect over second and third order derivatives of the thermodynamic potential, partial molar volume as well as the its derivative against mole number of the ionic liquid are calculated. Clear anomalies are detected in these magnitudes for all binary systems, very similar to those found for low molecular weight amphiphiles. Dependencies of this anomalous behavior against temperature and pressure are also analyzed.Ministerio de Ciencia, Innovación y Universidades | Ref. FIS2017-89361-C3-3-

A new methodology for determining the temperature of maximum density against pressure. Application to 2-propanol and ethanol aqueous solutions

Aqueous solutions of 2-propanol and ethanol are experimentally studied in order to obtain the location of the maximum of density versus temperature at high pressure. To this aim, a new technique based on measuring the pressure against temperature for several quasi-isochores was developed. These data are combined with isothermal compressibility, experimentally obtained from high pressure density data, to determine the isobaric thermal expansivity in the quasi-isochores. The temperature of maximum den- sity is obtained by detecting the temperature for which this magnitude becomes zero. These results are compared with those obtained using highly precise densitometry at atmospheric pressure and also with literature data. The differences between the temperature of maximum density for solutions and that of water are positive for very diluted solutions, but they become negative as concentration is raised, which constitutes a quite unusual behavior as compared with other systems. As pressure is raised, this anoma- lous behavior becomes much more pronounced with positive deviations that exceed 1.5 K at the highest pressures. The underlying microscopic picture that could explain the observed behavior is suggested.Ministerio de Ciencia y Tecnología | Ref. FIS2017-89361-C3-3-