Abstract
The ion effect on the structures and dynamics in aqueous solutions is specific. We carried out a series of molecular simulations to explore it at molecule level. Our simulation results suggest that the pairing preferences of a series of mono-atomic 1:1 ions follow Collins’ rule. The water-bridging ion pair is an important microscopic structure in aqueous solutions. In dilute KSCN and NaSCN aqueous solutions, the effect of anion and cation on the water mobility is additive and consistent with the Hofmeister series qualitatively and the prediction of Jones-Dole viscosity B-coefficient quantitatively. As the concentration increases, the cooperative effect of anion and cation and ion-cluster effect enhances. In concentrated aqueous solution, there is a retarding effect on the water dynamics exerted by any salt. The rotation of water is closely related to the hydrogen bond switching process. The rotation of water can be decomposed into a large-magnitude angular jump rotation and the frame diffusive rotation of the hydrogen bond pair. For anion, the strength of hydrogen bond directly formed by anion and water determines on the jump rotational mobility. The jump and frame diffusive rotations of water are both affected by the surrounding cations indirectly. The strength of cation effect is closely related to the charge density of cation.
Published Version
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