A Coarse-grained Approach to Understanding the Behavior of Polyelectrolyte Solutions

The behavior of polyelectrolyte solutions and coacervates is a topic of current interest. In the latter, oppositely charged polymers (and their counterions) are mixed in aqeous solution. We present a coarse-grained approach to modeling polyelectrolyte solutions, with a goal of studying large systems with adequate chemical detail, including explicit solvent. We focus on two polyions, namely polystyrene sulphonate (PSS) and polyvinylbutyltrimethyl ammonium (PVBTMA), in explicit solvent, with sodium and chloride counterions, respectively. In the development of a CG model, we find that the mapping scheme and partial charge distribution play a crucial role in the ability of the CG model to faithfully represent the atomistic model. The CG models are able to reproduce the conformational properties of single chains, as observed in atomistic simulations. Interestingly, the conformational properties of PVBTMA-Cl and PSS-Na are very similar, even though there are significant differences in the local correlations. We hope these models will aid in a molecular level understanding of complex coacervate behavior.