Effects of ion size and valence on ion distribution in mixed counterion systems of rodlike polyelectrolyte solution. I. Mixed-size counterion systemswith same valence

The influence of the counterion size is investigated in the mixed counterio n systems of the salt-free polyelectrolyte solution in a cylindrical cell m odel. The mixtures of two species of the counterion having the same valence and different size are simulated systematically by means of the Monte Carl o method in the primitive model of the rodlike polyelectrolyte solution. Th e results of the free fractions and the selectivity coefficients are compar ed with the numerical solutions of the Poisson-Boltzmann equation. The obse rved differences between both methods are explained in terms of the ion-ion correlations and the effect of finite ion size. (C) 2000 American Institut e of Physics. [S0021- 9606(00)50147-0].