Aggregation of rod-like polyelectrolyte chains in the presence of monovalent counterions

Using molecular dynamics simulations, it is demonstrated that monovalent counterions can induce aggregation of similarly charged rod-like polyelectrolyte chains. The critical value of the linear charge density for aggregation is shown to be close to the critical value for the extended-collapsed transition of a single flexible polyelectrolyte chain, and decreases with increasing valency of the counterions. The potential of mean force along the center of mass reaction coordinate between two similarly charged rod-like polyelectrolytes is shown to develop an attractive well for large linear charge densities. In the attractive regime, the angular distribution of the condensed counterions is no longer isotropic.