Rouse dynamics of polyelectrolyte solutions: Molecular dynamics study

We performed molecular dynamics simulations of dilute and semidilute polyelectrolyte solutions without hydrodynamic interactions to study Rouse dynamics of polyelectrolytes. Polyelectrolyte solutions are modeled by an ensemble of bead-spring chains of charged Lennard-Jones particles with explicit counterions. The simulations were performed for partially and fully charged polymers with the number of monomers N ) 25-373. We show that the simulations of the Rouse dynamics give qualitatively similar results to the experimentally observed dynamics of polyelectrolyte solutions. Our simulations showed that the chain relaxation time depends nonmonotonically on polymer concentration. In dilute solutions, this relaxation time exhibits very strong dependence on the chain degree of polymerization, τ ∼ N3. The chain relaxation time decreases with increasing polymer concentration of dilute solutions. This decrease in the chain relaxation time is due to chain contraction induced by counterion condensation. In the semidilute solution regime the chain relaxation time decreases with polymer concentration as c-1/2. In this concentration range the chain relaxation time follows the usual Rouse scaling dependence on the chain degree of polymerization, τ ∼ N2. At high polymer concentrations the chain relaxation time begins to increase with increasing polymer concentration. The crossover polymer concentration to the new scaling regime does not depend on the chain degree of polymerization, indicating that the increase in the chain relaxation time is due to the increase of the effective monomeric friction coefficient. The analysis of the spectrum and of the relaxation times of Rouse modes confirms the existence of the single correlation length ?, which describes both static and dynamic properties of semidilute solutions. 1.