Brownian simulations contribution to the study of ionic dynamics in aqueous solutions

We review some results concerning the dynamics of ionic solutions that we have recently obtained by Brownian dynamics simulations; we also present new results concerning the dynamical behavior of asymmetrical electrolytes (1-10 and 2-20 electrolytes). The Brownian dynamics treats the solution in the framework of the continuous solvent model, with a `soft-core' version of the primitive model. Both direct interactions and hydrodynamic interactions between solutes are taken into account in the calculations. The method allows one to obtain the self-diffusion coefficient of each ion and the electrical conductivity of the solution. The computed transport coefficients are in good agreement with experimental determinations in various cases (in aqueous solutions of 1-1 electrolytes as well as in aqueous solutions of micelles). We show that hydrodynamic interactions must be taken into account to obtain electrical conductivities in agreement with experiments. The effect of hydrodynamic interactions on the self-diffusion is also striking, especially in solutions of asymmetrical electrolytes. If this effect remains weak in simple electrolyte solutions and for small ions in 1-20 and 2-20 electrolyte solutions, it is great for macroions in latter solutions (increase of about 15 to 40%).