LIMITING LAWS AND COUNTERION CONDENSATION IN POLYELECTROLYTE SOLUTIONS .2. SELF-DIFFUSION OF SMALL IONS

The concepts developed in Part I of this series are applied to the self-diffusion of counterions and co-ions. The condensed counterions are assumed to have no mobility, while the uncondensed counterions and all co-ions execute Brownian motion subject to the locally inhomogeneous electric field created by the polyelectrolyte molecules. The polyelectrolyte field is assumed to have small amplitude, in analogy to the Debye-Hückel treatment of uncondensed mobile ions in Part I. The self-diffusion coefficients of the counterion and the co-ion are both less than the coresponding values in the absence of polyelectrolyte, but the coefficient for the counterion is much less than that for the co-ion. The results for the self-diffusion coefficient of the counterion in a salt-free polyelectrolyte solution are in good agreement with experimental data.