氯化钾水溶液微观结构的分子动力学模拟研究

氯化钾水溶液不同于氯化钠的，其在低温下只能形成无水盐和冰.现有研究表明在氯化钠水溶液中不仅存在着水分子连续分布的区域与离子团簇，而且这二者的物质组成也与该溶液所形成晶体的分别对应.为了探寻其他溶液中是否存在此类对应关系，并考察溶液的微观结构，本文采用分子动力学方法对氯化钾水溶液进行了研究，表明了该溶液的一些性质.氯化钾水溶液中K⁺-K⁺和Cl^--Cl^-径向分布函数的特征具有一致性，峰的最大值所对应的位置都分别相同，明显不同于氯化钠水溶液的.系列时刻下瞬态图像内O到其最近离子距离中最大值的统计结果表明氯化钾水溶液中存在着一定大小的水分子连续分布的区域，其平均尺寸至少为2.26 nm;瞬态图像中K⁺与其最近邻Cl^-之间的距离主要分布在0.28 nm～0.38 nm之间，占比约为97.4%;溶液中存在着较大和较小两类离子团簇，较大团簇的平均尺寸为1.73nm,平均离子数是25.0,其内部的离子与周围离子之间具有与氯化钾晶体类似的结构；这些结果表明氯化钾水溶液中也...

Molecular dynamics simulation of microstructures of potassium chloride aqueous solution

Unlike sodium chloride aqueous solutions (SCAS), potassium chloride aqueous solutions (PCAS) can only form anhydrous salt and ice at low temperatures. Some research results show that not only there are regions with continuous distribution of water molecules (RWs) and ion clusters in the SCAS, but also their composition corresponds to that of the crystals formed from the solution. In order to investigate whether there is such a corresponding relationship in other solutions and research their microstructures, the PCAS is studied by molecular dynamics method and some properties of the solution are gained. The radial distribution functions (RDFs) of K+-K+ and Cl--Cl- in the PCAS show that their characteristics are consistent with each other and the positions corresponding to the maximum of their peaks are the same respectively, different from those in the SCAS. The statistical results of the maximum distance between O and its nearest ions in transient images at a series of moments show that there are the RWs with average size of at least 2.26 nm in the PCAS. The distances between K+ and its nearest neighbor Cl- in transient images are mainly in the range of 0.28 nm~0.38 nm, accounting for about 97.4%. And the solution has the large ion clusters with average size of 1.73 nm and average ion number of 25.0 as well as small ones, moreover, the structures of their internal ions and surrounding ions are similar with those of potassium chloride crystals. These results show that micro heterogeneity and self-concentration effects also exist in the PCAS. The origins of each peak on the RDFs of ions are shown by comparing the relationships between distances of the maximum value of the peaks with the geometric ones of distances between ions in potassium chloride crystal and analyzing the ion transient images, and they are different from the SCAS. In addition, why the ion pairs and clusters are formed in the PCAS is explained by corresponding comparison and analysis; meanwhile, it is shown that the micro interaction of atoms and ions has an important influence on the micro heterogeneity of solutions. The results in this paper also show that the compositions of RWs and ion clusters in the PCAS are consistent with those of ice and potassium chloride crystals formed at low temperatures, and the structure of ion clusters is similar to the one of the potassium chloride crystal. Combined with the results of the SCAS, it is shown that solutions have the units with the composition similar to that of its crystals, which provides inspiration for understanding the formation of crystals in solutions.