Transport in electrolyte solutions: are ions Brownian particles?

Originally based on semiphenomenological equations, the transport properties of ions in electrolyte solutions can now be understood in terms of the Brownian motion. Thanks to the Smoluchowski equation or the mode-coupling theory (MCT) applied with the help of the mean spherical approximation (MSA), it is possible to describe the various transport quantities of ions in electrolyte solutions in the case of concentrated solutions (1-2 mol L−1) in agreement with Brownian dynamics simulations. These theories generalize the Onsager limiting laws, and they provide a test of the validity of the Brownian motion theories for ions.