Mechanism of chain collapse of strongly charged polyelectrolytes

We perform extensive molecular dynamics simulations of a charged polymer in a good solvent in the regime where the chain is collapsed. We analyze the dependence of the gyration radius Rg on the reduced Bjerrum length ℓB and find two different regimes. In the first one, called a weak electrostatic regime, Rg∼ℓ−1/2B, which is consistent only with the predictions of the counterion-fluctuation theory. In the second one, called a strong electrostatic regime, we find Rg∼ℓ−1/5B. To explain the novel regime we modify the counterion-fluctuation theory.