Molecular Dynamics Simulations of Polyelectrolyte Networks

Polyelectrolyte networks exhibit discontinuous volume transitions due to electrostatic interactions involving charged monomers and counterions. We have conducted molecular dynamics simulations of crosslinked polyelectrolyte networks of various molecular weights, counterion valencies, solvent dielectricities, and backbone charge densities. Counterions are modeled explicitly to overcome limitations imposed by the Debye--H\"{u}ckel approximation, and the solvent is treated implicitly. Our results show that the osmotic pressure of polyelectrolyte networks depends greatly on the strength of electrostatic interactions, and that an unstable regime develops along isotherms when the interaction is strong. The structures of constituent chains in polyelectrolyte networks are compared with those in neutral networks and those of uncrosslinked linear polyelectrolyte chains, and both similarities and differences are found. We also present our observations in the context of leading theories on the swelling of polyelectrolyte networks and on the condensation of counterions on rigid and flexible polyelectrolyte chains.