Microscopic origin of the deviation from Stokes-Einstein behavior observed in dynamics of the KSCN aqueous solutions:...

Molecular dynamics simulations were carried out to investigate the microscopic origin of the deviation from Stokes-Einstein behavior observed in the dynamics of KSCN aqueous solutions. When the solution becomes more concentrated, the rotational mobilities of SCN(-) and water bifurcate significantly as also observed in the experimental ultrafast infrared measurements. The translational mobilities of different components, on the other hand, have similar concentration dependences. Furthermore, when concentrating the solution, the mobilities increase slightly first and then reduce afterward. Our simulations revealed that these phenomena observed in the dynamics originate from the ion assembling in the solution. The RDF and pair residence time analysis further suggest the ion pairing effect has significant contribution to the ion assembling. Results herein thus provide a microscopic insight on the origin of the ion assembling phenomenon and its connection with various experimentally observable dynamical phenomena in the ionic solutions.