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.
Highlights
Supercritical water is used in a variety of chemical and industrial applications
Even the existence of hydrogen bonds in Supercritical water (SCW) was in controversy, it is generally accepted that hydrogen bonds are formed in supercritical conditions, hydrogen bonded networks do not exist[30,31,32,33,34,35]
The structural characteristics and physical properties of SCW for a wide range of temperatures (600–700 K) and pressures (230–290 bar) were determined by molecular dynamics (MD) simulations and compared with water equation of state (EoS) provided by NIST36 and data obtained from IAPWS37
Summary
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. Due to high SCW compressibility (directly related to microscopic density fluctuations17), by slightly adjusting the thermodynamic conditions, the structural, dynamical and transport properties drastically altered allowing the eclectic dissolution of polar or non-polar solutes[3,26,27,28,29,30]. This phenomenon is more intense in the vicinity of the critical point (1 < T/Tc < 1.1 and 1 < P/Pc < 1.2). Even the existence of hydrogen bonds in SCW was in controversy, it is generally accepted that hydrogen bonds are formed in supercritical conditions (in the non-high density states the hydrogen bonds are below the percolation threshold of 1.58), hydrogen bonded networks do not exist[30,31,32,33,34,35]
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