Role of solvation in ionic association across scales*

The phenomena of ionic association (or dissociation) are critical to many physical, chemical, and biological processes. The solvent, namely water, mediates these events through hydrogen bonding interactions within itself and with the solute ions/molecules. There is a competition between the solvent-solvent and solvent-solute interactions, which continues to vary as the solute concentration starts to increase. The events of ion pairing and clustering (small-scale ionic association) to nucleation to formation and growth of crystalline morphologies (large-scale ionic association) can be observed if the ion concentration is increased from a low concentration to a supersaturated state. In this presentation, we will discuss the role of solvent reorganization and exchange in mediating these processes in a supersaturated aqueous solution of Na₂SO₄. In addition, insight into the mechanism and kinetics of ionic association across scales will be provided. Gaining such insight has been possible through the utilization of molecular dynamics simulations, reaction rate theory, and modeling and measurements of Raman spectroscopy. We will elaborate on the extent of applicability of these tools in resolving local and large-scale structures and dynamics in aqueous electrolytes.