Structural, Dynamical, and Rheological Properties of KCl-Water Systems Across Varying Concentrations

The behavior of water in highly concentrated and supersaturated ionic solutions plays a critical role in a range of material and energy conversion processes, as well as in fundamental research. In this study, we examined the system's structural, dynamic, and rheological properties across a broad concentration range. On the structural front, we accurately reproduced experimental densities at low and near-saturation concentrations and further predicted density behavior beyond the saturation limit. Ion-ion correlations, increasingly significant at higher concentrations, showed a progressive increase in the first peak of the radial distribution function and a decline in the second peak. From a dynamical perspective, the system exhibits three distinct regimes at elevated concentrations: ballistic, caged (or trapped), and diffusive. The self-part of the van Hove correlation function displays slowed relaxation dynamics during the intermediate (trapped) regime, indicating hindered motion. Analysis of the non-Gaussian parameter confirms the presence of dynamical heterogeneity in the system. Lastly, we investigated the viscosity behavior and introduced a modified form of the Jones-Dole equation, which successfully captures the viscosity trend across the full range of concentrations.