Dynamics and Distribution of Counterions in the Vicinity of a Flexible Polyelectrolyte

Using molecular dynamics simulations, we investigated the dynamics and the distribution of the counterions within the Bjerrum layer of a polyelectrolyte with the degree of ionization spanning a range covering the counterion condensation transition point. We found that, during the condensation process, individual counterions enter and leave the vicinity of the polyelectrolyte molecule independently and randomly on a time scale comparable to the diffusion time across a Debye layer, and that the distribution of the counterions along the polyelectrolyte is not uniform. Instead, these counterions form clusters and that, within a cluster, they are packed with short range orientation order. Our simulations provide information on the detailed arrangement of the condensed counterions along a flexible polyelectrolyte, which is useful in understanding the electrophoretic behavior of these molecules, as well as the interaction between them.