Polyelectrolyte adsorption on an oppositely charged spherical polyelectrolyte brush

Coarse-grained molecular dynamics simulations are performed to investigate the interaction and complex formation of a spherical polyelectrolyte brush (SPB) consisting of uniformly distributed grafted polyelectrolytes (GPE) and an oppositely charged linear polyelectrolyte (LPE). This system is considered as a model for complexation of a polyelectrolyte and a soft nanoparticle. The effects of the LPE rigidity, length of the GPE chains, grafting density and core radius on complexation behavior are addressed. Depending on these parameters the GPE layer exhibits different structures, and acts on the LPE like a bare charged sphere, brush or star-like polyelectrolyte. Unlike the charged-sphere case, where the LPE binds to the solid body of the nanoparticle, the GPE arms can bind partly or completely to the LPE which in these cases is less affected by the core surface. The rigidity of the LPE also influences the conformational behavior of the brush layer. If the grafting density is small, the semiflexible LPE adopts a highly ordering solenoid conformation on the surface of the highly charged sphere. The ordered arrangement is disrupted as the GPE length increases. A higher ordering degree is also found for the semiflexible LPE at an intermediate core radius and relatively low grafting density. If the amount of surface charges is fixed, short GPEs suppress the complexation of the LPE with the SPB, compared to the cases of the long GPEs and bare charged sphere. However, the complexation propensity increases for lower grafting densities. Its dependence on the core radius is significantly different for flexible and semiflexible LPEs.