Experimental and molecular modeling of the structure and electrical conductivity of bulk ionic aqueous solutions: Sodium, potassium, and lithium chloride

We conducted a comprehensive analysis of the structure and dynamics of ionic aqueous solutions, focusing on sodium chloride (NaCl), potassium chloride (KCl), and lithium chloride (LiCl). Using molecular dynamics (MD) simulations with the OPLS + SPC/E model, we systematically explored the effects of varying ion concentrations and temperatures on several key properties. Specifically, we calculated radial distribution functions (RDFs), coordination numbers, diffusion coefficients (D), and electrical conductivity to elucidate the interactions between ions and surrounding water molecules. Our results indicate that the size of the ions significantly influences their solvation dynamics, with notable differences in the spatial arrangement of ions and their tendency to cluster in solution. The model successfully reproduces the experimental coordination numbers for Na⁺, K⁺, and Li⁺ reported in the literature. As ion concentration increases, we observed changes in diffusion behavior, with direct implications for the overall electrical conductivity of the solutions. Diffusion constants decrease as ion concentration increases. Heavier ions exhibit larger diffusion coefficients compared to lighter ions, which is a consequence of their interaction with the water network in their first solvation shell. Additionally, we experimentally implemented the open-ended coaxial reflection method to measure the electrical conductivity of NaCl, KCl, and LiCl in bulk solutions. Both MD simulations and experiments accurately replicate the electrical conductivity of NaCl, KCl, and LiCl across a concentration range from 0.1 M to 5 M. To test the applicability of our methodology, we calculated the electrical conductivity of a mixture of NaCl, KCl, and LiCl in water at 293.15 K. MD results are in agreement with experimental measurements. This study combines experimental and simulation methods to explore the interplay between ions in aqueous environments, providing valuable insights into the mechanisms governing ion transport and solvation in electrolyte solutions.