Rodlike Polyelectrolytes in the Presence of Monovalent Salt

We investigate the properties of rigid polyelectrolyte solutions in the presence of monovalent salt. The free energy within the Debye−Huckel-Bjerrum (DHBj) theory (Fisher, M. E.; Levin, Y. Phys. Rev. Lett. 1993, 71, 3826) is constructed. It is found that at thermodynamic equilibrium the polyelectrolyte solution consists of clusters composed of one polyion and various counterions. The distribution of the cluster densities is determined by finding the minimum of the Helmholtz free energy. The osmotic pressure and the average charge of the cluster are found and their dependence on Manning parameter ξ is elucidated. A good agreement with the experimental results is obtained.