Counterion correlations and attractions in dense polyelectrolyte solutions

We study concentrated solutions of highly charged polyelectrolyte solutions beyond the mean-field approximation by explicitly taking into account the effects of both counterion and polymer chain fluctuations. One part of the fluctuating counterion densities moves freely throughout the bulk. The second counterion density component consists of a fraction of counterions fluctuating along the length of the chains. The degree of condensation and the effective intra-chain potential are determined self-consistently. We observe the effects of this interaction which is attractive over short distances and can lead to a collapse as a sufficiently high level of counterion condensation is achieved. (letter to the editor)