Entanglements and Dynamics of Polyelectrolytes in Concentrated Solutions and Complexes

We performed coarse-grained molecular dynamics simulations of polyelectrolyte solutions and mixtures of oppositely charged chains with different degrees of polymerization. Analysis of the simulation results for the mean-square displacement of the monomers belonging to the central part of the chain and the chains’ centers of mass shows that the chains’ dynamics is a combination of constraint release and chain reptation in the confining tube. The constraint release appears to play a dominant role in mixtures of positively and negatively charged chains with intermediate and low degrees of polymerization. The degree of polymerization between entanglements N_e of the tube and super tube in systems of charged chains scales with solution concentration as N_e~ρ^-2 and has corresponding packing number P_e = 18.45+/−0.93. This is qualitatively different from the behavior of similar composition mixtures of neutral chains where in addition to the N_e~ρ^-2 scaling dependence, the degree of polymerization between entanglements for the super tube demonstrates a N_e~ρ^-4/3 concentration dependence with corresponding packing number P_e = 6.64+/−0.19.