Ionic Mobility and Ultrafast Solvation:  Control of a Slow Phenomenon by Fast Dynamics

What determines the ionic conductivity of an electrolyte solution has remained a problem of great interest to chemists for more than a century.1-3 Such long-standing interest stems not only from its relevance in many chemical and biological applications, but also from the many fascinating, often anomalous, behaviors that ionic conductivity exhibits in a large number of solvents. Most often discussed of these properties are the concentration and the nonmonotonic ion size dependencies. However, even after century-old debates and discussions, neither of the above two problems has been satisfactorily resolved. The mobility of an ion in a polar solvent is determined by its complex interactions with the surrounding polar molecules; these interactions are long-ranged and anisotropic. In addition, the dynamics of polar liquids were very poorly understood until recently.