Computer simulations of polyelectrolyte chains in salt solution

Abstract

We use Monte Carlo simulation methods to study the conformational properties of a partially ionized polyelectrolyte chain in 1:1 electrolyte solution at room temperature and the distribution of salt ions around the polyion chain. The present results are extensively compared with our previous work on polyelectrolyte chains interacting via a screened Coulomb potential with no ions. The two models give similar conformational properties for lower degrees of ionization of the polyion and/or higher salt concentrations. For higher degrees of ionization and/or lower salt concentrations, the counterions seem to position themselves so as to enhance their effect over the screening model counterpart, and the polyelectrolyte chains are generally much more coillike than in the screening model. Our conclusions partly agree with Valleau’s work on shorter chains. Although some aspects of counterion condensation are evident, our results do not quantitatively agree with the limiting form of Manning’s counterion condensation theory, since conformational properties of the chain continue to depend on the ionization beyond the critical linear charge density in his theory. Simulations for fully ionized chains were found to behave erratically and most of these results had to be discarded.