Hydrodynamic effect in diffusion-controlled reaction

A calculation is presented for the effect of the hydrodynamic interaction on the diffusion-controlled rate coefficient for particles that coalesce by diffusion under the influence of an interaction potential. The hydrodynamic effect is found to make a substantial reduction in the rate compared to the Debye model which includes only the effects of diffusion and the forces between the reacting particles. For the case where the particles are hard spheres the reduction is 46%. For ionic species the reduction varies between 25% and 60% depending on the extent of attraction or repulsion.