Rodlike Model for a Polyelectrolyte Solution with Mono- and Divalent Counterions

Abstract

The charge distribution of simultaneously present mono‐ and divalent counterions and the degree of ion binding is calculated for the simplified rodlike model of polyelectrolyte solution without addition of low‐molecular‐weight electrolyte. Divalent ions concentrate much more than monovalent ions in the vicinity of the charged macromolecule and hence push the monovalent ions farther away. As a consequence, the degree of binding of divalent ions increases and that of monovalent ions decreases with increasing of the equivalent fraction of the other type of ions. This agrees with the dependence of the selectivity coefficient of ion exchange on the fraction of ionic species within the resin phase.