Abstract
The conformational properties of single flexible polyelectrolytes in solutions with added salt are investigated by means of Monte Carlo simulations. Upon addition of multivalent salt, the polyelectrolyte chain initially undergoes the well-known conformational collapse. At higher multivalent salt concentration the chain subsequently reexpands, in accordance with experimental observations and theoretical predictions. These conformational changes constitute the counterpart of reentrant condensation exhibited by polyelectrolytes under less dilute conditions. We find that the charge of the polyelectrolyte can be overcompensated in the reexpansion region. For the case of monovalent salt, neither chain reexpansion nor charge inversion are observed. We investigate the role of ion excluded volume on chain conformation and charge inversion and find that the degree of reexpansion and overcharging both decrease with ion size. Our results suggest that this behavior is caused by ionic association, which effectively reduces the salt valency.