(70q) Analysis of Dehydration Process in Crystallization of Nacl by Molecular Dynamics Simulations

The behavior of solute ions in a supersaturated NaCl solution has been investigated by molecular dynamics (MD) simulation. The density profile of water molecules and solute ions in the vicinity of the interfaces between NaCl(100) crystal and supersaturated NaCl solution was obtained. Diffusion coefficients of water molecules in the solution were calculated as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the vicinity of the interfaces was different from those of bulk solution owing to the effect of the electric fields depending on the surface charge. Therefore, the electric field was applied to the supersaturated solutions and the dehydration phenomenon occurring in the process of crystal growth was discussed. As the electric field increased, it was observed the Na+ keeping strongly hydrated structure broke out by the electric field. However, the breakout of hydration structure was not affected on the electric field as the supersaturation increased. This reason is because the screening by clusters occurs in the high supersaturated solution. Electric force from surface ions acts on the clusters, and breaks the cluster structures. Then, the cluster broken out by the electric field adsorbed on the crystal surface.