Anomalies of Liquid Water

Abstract Water at low temperatures ( T < 300 K) reveals a multitude of unusual physico‐chemical properties, which originate from the strong directivity of the hydrogen bonds. This directivity forces the molecules into a tetrahedral arrangement of first neighbors and thus leads to a poor packing efficiency. All anomalies of the liquid become more pronounced in the metastable range below the melting pressure curve. In the following article, methods for the investigation of the supercooled range are presented. A few anomalous static and dynamic properties are described and compared with the properties of normal liquids. The experimental results are discussed in the context of computer simulations and the more recent theories on cold water. It can be concluded that the anomalies of water, for instance the density maximum of the liquid phase and the initial decrease in viscosity with pressure, are confined to the pT ‐range: T < 300 K, p ≲ 200 MPa. At these pressures, lowering the temperature leads to an unexpected behavior of almost all physical properties. They seem to approach a phase transition at T ≃ ( T M − 50 K), the nature of which has not yet been fully characterized. This phenomenon has hitherto been observed only in supercooled water.—In the future it will be possible to use supercooled aqueous solutions for kinetic studies, thus expanding the available dynamic range for the investigation of aqueous solutions considerably.