It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems.In light of this,we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations.Via varying polydis-persity,grafting density,and solvent selectivity,the effects of electrostatic correlation and excluded volume are focused,and rich phase behaviors of binary mixed polyelectrolyte brush are predicted,including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density.To pinpoint the mechanism of surface structure formation,the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully.Also,electrostatic correlations,manifested as the bridging through trivalent counterions,are examined by identifying four states of trivalent counterions.Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.