Some Aspects of the Liquid Water Thermodynamic Behavior: From The Stable to the Deep Supercooled Regime

Abstract

Liquid water is considered to be a peculiar example of glass forming materials because of the possibility of giving rise to amorphous phases with different densities and of the thermodynamic anomalies that characterize its supercooled liquid phase. In the present work, literature data on the density of bulk liquid water are analyzed in a wide temperature-pressure range, also including the glass phases. A careful data analysis, which was performed on different density isobars, made in terms of thermodynamic response functions, like the thermal expansion αP and the specific heat differences CP−CV, proves, exclusively from the experimental data, the thermodynamic consistence of the liquid-liquid transition hypothesis. The study confirms that supercooled bulk water is a mixture of two liquid “phases”, namely the high density (HDL) and the low density (LDL) liquids that characterize different regions of the water phase diagram. Furthermore, the CP−CV isobars behaviors clearly support the existence of both a liquid–liquid transition and of a liquid–liquid critical point.

The Water Polymorphism and the Liquid–Liquid Transition from Transport Data

“…A comparison of the thermal behaviors of all the evaluated C P,con f isobars, in particular, the observed maxima and the evolutions of the diverging behaviors, clearly reveals the presence of the LLT and, with a reasonable approximation, the LLCP locus in the phase diagram. This latter situation is fully consistent with recently studies on the water thermodynamic functions obtained from experimental data [35,44,69] and proper MD simulations [36][37][38][39]68]. Finally, we underline that the observed significant configurational evolutions due the liquid water polymorphism are related to the local potential minima, known as inherent structures (ISs), surrounded by potential energy basins [65].…”

“…In this case, the increase in the temperature interval within the metastable region highlights both a maximum, and thus a WL point in C P,con f at 200 MPa (∼195 K) and a very pronounced divergent behavior at 175 MPa. In addition, the maximum value in C P,con f at 200 MPa ( 44.3 JK −1 mol −1 ) is smaller than that measured at 0.1 MPa ( 66.1 JK −1 mol −1 ), whereas the highest value obtained for the 175 MPa isobar is 72.7 JK −1 mol −1 at 206 K. These further data, in agreement with the precedents due to self-diffusion, not only give confirmation of the presence of a LLT but also indicate the presence of LLCP located in the following region of the phase diagram: an isobar P C between 175 and 200 MPa and a critical temperature 195 < T C < 206 K. Such a result obtained from dynamical data inside the no man's land, also by considering the full agreement with the finding coming from the isothermal compressibility (evaluated from the density data) studies [35,44,69], undoubtedly provide crucial information regarding our understanding of the strange behavior of liquid water. We stress that this resulting and complex evolution of the configurational modes of liquid water clearly shown both by the S con f and C P,con f isobars due to its polymorphism is certainly the result of its underlying energy configuration: the energy landscape or inherent basins of energy [65].…”

Core-softened water–alcohol mixtures: the solute-size effects

“…Recent findings indicates that the water anomalies are related to the Liquid-Liquid Critical Point (LLCP) [16,81]. Although hypothetical and not observed (yet) in experiments, there is strong and many evidences that the water liquid polymorphism in the supercooled regime ends in the LLCP [14,82]. We can estimate the critical point location using the isothermal density derivatives of the pressure [83]…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…Articles [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] can be attributed to the first of the thematic areas indicated in the PCCP Section, and the distribution of these articles into the above categories is presented in Table 2 . As it can be seen, of the four types of articles established by the magazine’s standards ( Reviews , Originals, Communications , Editorials ), only the first two are presented here.…”

“…Two publications [ 7 , 19 ] provide data on the specific interactions in “guest-host” systems. Occasionally, there are works devoted to other aspects related to intermolecular interactions, in particular, to the formation of liquid crystal systems [ 8 ], supercooled bulk water [ 11 ], and liquid-liquid extraction aimed at separating individual heavy metals from aqueous solutions [ 10 ].…”