Abstract
The interface structure between NaCl crystal and its solution has been investigated at the saturated concentration of 298 K by molecular dynamics simulations. We have found that there are many fine structures at this complex interface. Near the surface of crystal, most of Na+ only coordinate with water molecules, while almost all Cl– coordinate with Na+ in addition to water molecules. An ion coordinating with more water molecules is farther away from the epitaxial position of lattice. As approaching to the interface, the first hydration shell of ions has the tendency of being ordered, while the orientation of dipole of water molecules in the first hydration shell becomes more disordered than that in the solution. Generally, the first hydration shell of Na+ is less affected by nearest Cl–, whereas the first hydration shell of Cl– is significantly affected by nearest Na+.
Highlights
In nature and daily life, the solid−liquid interface (SLI) between ionic crystals and solutions is ubiquitous
Large density oscillations and layerlike structure are observed near the interface, which is universal in SLI systems
(2) The coordination between anions and cations has a little effect on the first hydration shell (FHS) of Na+ but has a significant impact on all aspects of the FHS of Cl−. (3) As approaching to the interface, the hydration structure of ions tends to be ordered; it is unconventional that the dipole orientation of water molecules in the FHS has the tendency of disordering
Summary
In nature and daily life, the solid−liquid interface (SLI) between ionic crystals and solutions is ubiquitous. Due to the strong influence of the periodic character of crystal and long-range Coulomb interaction, the SLI between the ionic crystal and solution is usually more complicated than that of simple metal solid−liquid interfaces.[1,3,4,7,16,17] Compared to experimental methods, computer simulation is a powerful tool to obtain atomic scale information. The distribution of water molecules in the ionic hydration structure around the interface is strongly modified by the local environment of ions
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