Anionic effects on the structure and dynamics of water in superconcentrated aqueous electrolytes
Journal
RSC Advances
Date
2019.01.02
Abstract
Dissolved ions in aqueous solutions are ubiquitous in a variety of systems and the addition of ions to water gives rise to dramatic effects on the properties of water. Due to a significant role of ions in the structure and dynamics of water, the ionic conditions, such as the ion type and concentration, have been considered as critical factors. Here we study the effects of anions on the structure and dynamics of water in aqueous electrolytes for various lithium salt concentrations via extensive molecular dynamics simulations. Our results demonstrate that a certain amount of salt is needed to show the different properties of water caused by the presence of the different type of anions. Below the cutoff concentration, the most features of water show the same characteristics in despite of the existence of different anions. In the superconcentrated limit, we find that the full disruption of the hydrogen bond network between water molecules occurs for most anions investigated, indicating that the effect of the water-water interaction becomes negligible. However, a certain type of anion could enhance an ion-pairing of cations and anions and the water-water interaction remains considerable even in the superconcentrated limit. We further investigate the cationic and anionic hydration shell structures and dynamics, revealing their dependences on the anion type and the salt concentration. Finally, we observe that the anionic effects on water continue to the dynamics of water molecules, such as an anionic dependence of the onset of the subdiffusive translation and the anisotropic rotation.