State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China.
Department of Chemistry, Bohai University, Jinzhou 121013, China.
Proc Natl Acad Sci U S A. 2017 Sep 19;114(38):10023-10028. doi: 10.1073/pnas.1707453114. Epub 2017 Sep 5.
Water dynamics in concentrated ionic solutions plays an important role in a number of material and energy conversion processes such as the charge transfer at the electrolyte-electrode interface in aqueous rechargeable ion batteries. One long-standing puzzle is that all electrolytes, regardless of their "structure-making/breaking" nature, make water rotate slower at high concentrations. To understand this effect, we present a theoretical simulation study of the reorientational motion of water molecules in different ionic solutions. Using an extended Ivanov model, water rotation is decomposed into contributions from large-amplitude angular jumps and a slower frame motion which was studied in a coarse-grained manner. Bearing a certain resemblance to water rotation near large biological molecules, the general deceleration is found to be largely due to the coupling of the slow, collective component of water rotation with the motion of large hydrated ion clusters ubiquitously existing in the concentrated ionic solutions. This finding is at variance with the intuitive expectation that the slowing down is caused by the change in fast, single-molecular water hydrogen bond switching adjacent to the ions.
在许多物质和能量转换过程中，如水系可再充电离子电池中电解质-电极界面的电荷转移，浓缩离子溶液中的水动力学起着重要作用。一个长期存在的难题是，所有电解质，无论其“结构形成/破坏”性质如何，在高浓度下都会使水的旋转速度变慢。为了理解这种效应，我们对不同离子溶液中水分子的重取向运动进行了理论模拟研究。使用扩展的Ivanov 模型，将水分子的旋转分解为大振幅角跳跃和较慢的框架运动的贡献，后者以粗粒度方式进行了研究。与大分子附近的水旋转具有一定的相似性，发现这种普遍的减速主要是由于慢的、集体的水旋转与普遍存在于浓缩离子溶液中大的水合离子簇的运动之间的耦合所致。这一发现与直觉期望相反，即减速是由离子附近快速的、单个水分子氢键的变化引起的。
