Charged Polymer/Nanoparticle Mixtures: Monte Carlo Simulations

We used Monte-Carlo simulations to study the formation of complexes between charged polymers (or polyelectrolytes) with oppositely charged spherical nanoparticles. We presented the model, the Monte Carlo numerical method and investigated the effects of the ionic concentration of the solution, polyelectrolyte rigidity (or flexibility), linear charge density, and surface charge of the nanoparticles. Polyelectrolyte adsorption is controlled by several competing effects. On the one hand, rigidity and electrostatic repulsion force the polyelectrolyte to adopt extended conformations and limit the number of monomers which may be attached to the nanoparticles. On the other hand, electrostatic attractive interactions between the particle and the polyelectrolyte monomers force the chain to undergo a structural transition and collapse at the particle surface. By increasing the intrinsic rigidity, we observed a transition from disordered and strongly bound complexes to a situation where the polymer touches the particles over a finite length, while passing by the formation of a solenoid conformation. We found that the critical ionic concentration at which adsorption/desorption is observed rapidly increases with the increase of the nanoparticle surface charge density in good agreement with experimental data dealing with the formation of complexes between micelles and oppositely charged polyelectrolytes. Adsorption is also promoted by decreasing the chain stiffness or decreasing the salt concentration for a given chain length.