Han Sungho
CAE Group, Platform Technology Lab, Samsung Advanced Institute of Technology Suwon Gyeonggi 16678 Korea
RSC Adv. 2019 Jan 2;9(2):609-619. doi: 10.1039/c8ra09589b.
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 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 different types of anion. Below the cutoff concentration, most features of water show the same characteristics in spite of the presence of different anions. In the superconcentrated limit, we find that 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 dependence on the anion type and the salt concentration. Finally, we observe that the anionic effects on water extend to the dynamics of water molecules, such as an anionic dependence of the onset of subdiffusive translation and anisotropic rotation.
水溶液中的溶解离子在各种系统中普遍存在，向水中添加离子会对水的性质产生显著影响。由于离子在水的结构和动力学中起着重要作用，离子条件，如离子类型和浓度，被视为关键因素。在此，我们通过广泛的分子动力学模拟研究了不同锂盐浓度下阴离子对水电解质中水的结构和动力学的影响。我们的结果表明，需要一定量的盐才能展现出由不同类型阴离子的存在所导致的水的不同性质。在临界浓度以下，尽管存在不同的阴离子，水的大多数特征仍表现出相同的特性。在超浓极限情况下，我们发现对于所研究的大多数阴离子，水分子之间的氢键网络会完全被破坏，这表明水 - 水相互作用的影响变得可以忽略不计。然而，某一类型的阴离子可以增强阳离子和阴离子的离子对形成，并且即使在超浓极限情况下，水 - 水相互作用仍然相当可观。我们进一步研究了阳离子和阴离子的水化层结构及动力学，揭示了它们对阴离子类型和盐浓度的依赖性。最后，我们观察到阴离子对水的影响延伸到了水分子的动力学，例如亚扩散平移起始和各向异性旋转对阴离子的依赖性。
