The water thermodynamics is characterized by polydispersity, which determines its structural and dynamic properties. This is due to the specifics of its characteristic bond: the hydrogen bond (HB). The isobars of the two fundamental thermodynamic functions, the isothermal compressibility (KT(P.T)) and the isobaric expansivity (αP(P,T)), show the presence of a temperature T*≃315±5 K where both have a singular behavior. In this work, by carefully considering the thermal properties of the isobars of density ρ, specific heat CP and the self-diffusion DS, we suggest the universality characteristics of this temperature. In addition, by analyzing the average intermolecular distance dOO, in the same area of the P-T phase diagram, we demonstrate that such realities are due in the supercooled liquid state to the ratio between its two characteristic phases: the low-density liquid (LDL due to HB) and the HDL (which entirely characterizes the remaining parts of the phase diagram).
Mallamace et al. (Fri,) studied this question.