Polyelectrolyte adsorption on an oppositely charged spherical particle. Chain rigidity effects

We used Monte Carlo simulations to study the formation of complexes between a flexible, seiniflexible, and rigid polyelectrolyte and an oppositely charged spherical particle. Polyelectrolyte adsorption on a small particle, whose surface curvature effect is expected to limit the amount of adsorbed monomers, was considered. We focused on the effects of the intrinsic polyelectrolyte rigidity and ionic concentration of the solution and investigated the adsorption/desorption limit and conformation of the adsorbed polyelectrolyte. Polyelectrolyte adsorption is controlled by several competing effects such as the electrostatic confinement energy of the chain due to the electrostatic repulsions between the charged monomers, polyelectrolyte intrinsic flexibility, and electrostatic attractive interaction between the polyelectrolyte monomers and the particle. On one hand, rigidity-and electrostatic repulsions force the polyelectrolyte to adopt extended conformations and limit the number of monomers that may be attached to the particle. 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. In particular, by increasing the intrinsic rigidity, we observed a transition from a disordered and strongly bound complex to a situation where the polymer touches the particle 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 is rapidly decreasing with the polyelectrolyte intrinsic rigidity, and the amount of adsorbed monomers has a maximum value for semiflexible chains. Adsorption is thus promoted by decreasing the chain stiffness or decreasing the salt concentration for a given chain length.