Ionic Self-Diffusion in Concentrated Aqueous Electrolyte Solutions

A self-consistent microscopic theory is developed to understand the anomalously weak concentration dependence of ionic self-diffusion coefficient $D_{\mathrm{ion}}$ in electrolyte solutions. The self-consistent equations are solved by using the mean spherical approximation expressions of the static pair correlation functions for unequal sizes. The results are in excellent agreement both with the known experimental results for many binary electrolytes and also with the new Brownian dynamics simulation results. The calculated velocity time correlation functions also show quantitative agreement with simulations. The theory also explains the reason for observing different $D_{\mathrm{ion}}$ in recent NMR and neutron scattering experiments.