COLLAPSE OF POLYELECTROLYTE MACROMOLECULES BY COUNTERION CONDENSATIONAND ION-PAIR FORMATION - A MOLECULAR-DYNAMICS SIMULATION STUDY

The conformational properties of single polyelectrolyte chains of vari ous lengths in the presence of counterions are investigated by molecul ar dynamics simulations. For Coulomb interaction strengths below the c ritical value for Manning condensation, the molecular chain exhibits a n increase of the radius of gyration and of the end-to-end distance wi th increasing interaction strength. Above this critical value, counter ions condense on the chain and ion pairs are formed. The ion pairs pos sess a net attraction such that beyond a certain interaction strength the chain with the condensed ions collapses into a dense coil. The sca ling behavior of the radius of gyration and the end-to-end distance wi th changes in the number of bonds is discussed for various Coulomb int eraction strengths.