STRUCTURE OF SALT-FREE LINEAR POLYELECTROLYTES IN THE DEBYE-HUCKEL APPROXIMATION

We examine the effects of the common Debye-Huckel approximation used i n theories of polyelectrolytes. Molecular dynamics simulations using t he Debye-Huckel pair potential of salt-free polyelectrolytes have been performed. The results of these simulations are compared to earlier ' 'Coulomb'' simulations which explicitly treated the counterions. We re port here the comparisons of the osmotic pressure, the end-to-end dist ance and the single chain structure factor. In the dilute regime the D ebye-Huckel chains are more elongated than the Coulomb chains implying that the counterion screening is stronger than the Debye-Huckel predi ction. Like the Coulomb chains the Debye-Huckel chains contract signif icantly below the overlap density in contradiction to all theories. En tropy thus plays an important and sorely neglected role in theory.