(716e) Coarse-Grained Simulations of Weak Polyacid Titration in Explicit Salt

The titration behavior of weak polyelectrolytes is important in developing technologies for nanofiltration membranes, drug delivery, and gene therapy. Here, we detail computer simulations aimed at providing a comprehensive picture of the effects salt, associative interactions, and polymer structure have on the charging and conformations of weak polyelectrolytes. This work utilizes a hybrid Monte Carlo/Molecular Dynamics method, focusing on the coil-to-globule transition of linear and star polyelectrolytes in the presence of explicit salts, and offers two key insights. (1) Weak polyelectrolyte titration in the presence of monovalent salt may be qualitatively, but not quantitatively, described by Debye-screening models, as including explicit salt changes the order of the coil-globule phase transition. (2) Charging and swelling behavior in the presence of divalent counterions deviates significantly from screening models and leads to highly charged collapsed conformations for both linear and star polyelectrolytes. We further discuss the relevance of these observations to recent experimental studies and charge-associating materials. These simulations can serve as a starting point to understand the complexation between weak polyelectrolytes in the explicit ion limit and further to model the ion rejection in self-assembled copolymer membranes with weak polyelectrolytes lining the pore interiors.