Collapse of Stiff polyelectrolytes due to counterion fluctuations

The effective elasticity of highly charged stiff polyelectrolytes is studie d in the presence of counterions, with and without added salt. The rigid po lymer conformations may become unstable due to an effective attraction indu ced by counterion density fluctuations. Instabilities at the longest (inter mediate) length scales may signal a collapse to globule (necklace) states, respectively. In the presence of added salt, a generalized electrostatic pe rsistence length is obtained, which has a nontrivial dependence on the Deby e screening length. [S0031-9007(99)09257-1].