Charge Regulation Effects on Polyelectrolyte-Mediated Nanoparticle Interactions

Controlling surface charge through charged polymers is key to developing nanomaterials with tunable properties and functions. We investigate how charge regulation (CR) affects interactions between oppositely charged nanoparticles (NPs) mediated by a polyelectrolyte (PE) in electrolyte solutions. Using a hybrid CR Monte Carlo / molecular dynamics framework, we investigate how pH, salt concentration, and polymer length affect the NP surface charge and PE adsorption. To assess the impact of CR, results are compared with simulations performed under constant charge (CC) conditions. CR enhances PE adsorption on NP surfaces compared to the CC model, where polymer bridging dominates over a broad range of NP separations. This stronger adsorption under CR leads to a weak osmotic repulsion, whereas the CC case exhibits stronger attraction from bridging. CR effects are most significant at low salt concentrations but diminish under high-salt screening. These findings emphasize the importance of incorporating charge regulation when modeling nanoparticle interactions in complex electrolytic environments.