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 effective interaction potential between two rod-like polyelectrolyte chains is measured, and is related to the angular distribution of the condensed counterions. 
Anoop Varghese, R. Rajesh, Satyavani Vemparala
cond-mat.soft cond-mat.stat-mech