Dilute solutions of strongly charged flexible polyelectrolytes in poor solvents: Molecular dynamics simulations with explicit solvent

The behavior of dilute salt-free solutions of charged flexible polymer molecules in poor solvents is studied using molecular dynamics simulations. The polymer molecule is modeled as a chain of charged spheres, the counterions are modeled as charged spheres, and the solvent molecules are incorporated explicitly and modeled as uncharged spheres. The pearl-necklace structures predicted by theory and observed in simulations with implicit solvent are not clearly seen in snapshots of chain conformations, although there is a clustering of monomers. An analysis of the single chain structure factor using a Kratky plot is misleading and not consistent with an analysis of cluster formation or a visual examination of snapshots. The conformational dynamics, as manifested in the decay of the intermediate scattering function, is relatively insensitive to solvent quality, except for the poorest solvent conditions. In this case the single chain structure factor displays oscillations, and the intermediate scattering function displays a dynamic slowing down at corresponding wave vectors. The simulations suggest that the presence of explicit solvent molecules can be an important aspect of polyelectrolyte behavior in poor solvents.