Supercritical water anomalies in the vicinity of the Widom line

Abstract

Supercritical water is used in a variety of chemical and industrial applications. As a consequence, a detailed knowledge of the structure-properties correlations is of uttermost importance. Although supercritical water was considered as a homogeneous fluid, recent studies revealed an anomalous behaviour due to nanoscale density fluctuations (inhomogeneity). The inhomogeneity is clearly demarked through the Widom line (maxima in response factions) and drastically affect the properties. In the current study the physical properties of supercritical water have been determined by classical molecular dynamics simulations using a variety of polarized and polarizable interatomic potentials. Their validity which was not available at supercritical conditions has been assessed based on the ability to reproduce experimental data. Overall, the polarized TIP4P/2005 model accurately predicted the properties of water in both liquid-like and gas-like regions. All interatomic potentials captured the anomalous behaviour providing a direct evidence of molecular-scale inhomogeneity.

From Critical Point to Critical Point: The Two-States Model Describes Liquid Water Self-Diffusion from 623 to 126 K

“…Subsequently, the evaluated configuration-specific heat displays a well-defined maximum at the same temperature, which is in agreement with the LLCP hypothesis [ 53 , 66 ] and goes toward a diverging-like behaviour along the liquid-vapour coexistence line. It is worth mentioning that for pressures higher than the critical one (P = 220.6 bar), a Widom line, where specific heat assumes its maximum value, departs from the high temperature critical point [ 67 ].…”

“…The thermodynamic implications regarding the existence of two main, different liquid states with different densities must take into consideration the hydrogen bond ability of water molecules. It is now demonstrated that HBs can also form in supercritical conditions, but no HB networks can exist at all [ 67 , 68 , 69 ]. The knowledge of dynamic and thermodynamic quantities, including and at temperatures as high as the critical one, is essential both for fundamental research and industrial applications.…”

Deciphering The Molecular Mechanism Of Water Boiling At Heterogeneous Interfaces

“…More speci cally, in respect to bulk properties, SPC/E water model reasonably predicts all the physical properties (density, compressibility, self-diffusion coe cient and dielectric constant). The Lorentz-Berthelot combining rule was used to determine the unlike Lennard-Jones parameters [54][55][56] .…”

Thermodynamics and Dynamics of Supercritical Water Pseudo‐Boiling

“…An offset both in temperature and pressure was applied in order to reproduce the experimental critical point (temperature and pressure). [ 34 ] In the CNs calculation, a cut off of 3.5 Å was used, and for the hydrogen bonds, a geometric criterion based on the oxygen–oxygen distance ( d OO < 3.5 Å) [ 56 ] and hydrogen–oxygen–hydrogen angle (HOH < 30°) was used. [ 34 ]…”

“…[ 32 ] The simulation techniques used to analyze the structure of supercritical fluids are reviewed in ref. [ 33 ] and for water these include mostly molecular dynamics (MD) simulations [ 34–40 ] (ab initio MD [ 30,41 ] ), Monte Carlo simulations [ 27,42,43 ] (Reverse Monte Carlo [ 39 ] ), and density functional theory. [ 30 ] The above‐mentioned studies have been mainly focused on changes in the scH 2 O structure described in terms of hydrogen bonding.…”