Phase diagram of hydration shells in ionic solutions

Authors:

• Irena Danielewicz-Ferchmin

Abstract

Thermodynamic and electrostatic approach to hydrogen-bonded liquids is applied to the hydration problem of diluted ionic solutions. Electric permittivity of water is calculated as a function of reduced distance from the center of an ion. The mean cosine between the electric dipole of water molecule and Coulomb field directions plays the role of order parameter. A phase diagram of water in the electric field of solute ions is proposed. In the diagram, the sets of ions can be grouped according to the energy of the dipoles of water molecules in the field of an ion. Agreement between the present approach and recent IR, ND, and Xr diffraction studies is discussed. In particular, water around Sr²⁺ ion is seen as being in, or close to, a critical state where two different phases of water in electric field merge into a single one. © 1995 American Chemical Society.