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 re-gions with continuous distribution of water molecules(RWs)and ion clusters in the SCAS,but also their compo-sition 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 mo-ments 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 a-bout 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 potas-sium chloride crystal and analyzing the ion transient images,and they are different from the SC AS.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 heter-ogeneity 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 struc-ture 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 inspira-tion for understanding the formation of crystals in solutions.
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维普
