Attraction between like-charged polyelectrolytes in the extended condensation theory.

The interaction free energy of like-charged polyelectrolytes in solution is calculated in the framework of the extended counterion condensation theory, recently given by Schurr and Fujimoto, Biophys. Chem. 2002, 101-102, 425-445. For sufficiently high linear charge density, the electrostatic free energy of two parallel identical rigid polyelectrolytes as a function of the distance between them shows a minimum at distances in the range of nanometers, increasing with the Debye screening length. This effect is due to the increasing of the counterion condensed charge and condensation volume as the two polyelectyrolytes approach.