Assembly of nano-particles on diblock copolymer brushes: toward laterally nano-structured composites

Abstract

We have studied the self-assembly of nano-particles (NPs) at the surface of microphase-separated AB diblock copolymer brushes in a selective solvent by means of dissipative particle dynamics (DPD) simulations. The structure of such nano-composites depends both on the morphology of the underlying brush which is basically determined by chain composition f_B and solvent selectivity τ_B, and on specific parameters of the NPs added such as polymer compatibility a_BP, solvophobicity a_PS, and concentration φ, where a_ij are the DPD interaction parameters. The immense parameter space is explored within a coarse-grained model that contains polymer A and B beads, solvent (S), nano-particle (P), and wall (W) beads. For composites with B-like nano-particles, i.e., NPs that are covered by polymer B ligands, we construct the phase diagram in the f_B − φ space. For B-unlike NPs, it is found that the solvophobicity of the particles set by a_PS is crucial for the spreading of nano-droplets. We show that in principle microphase-separated diblock copolymer brushes can be used to create ordered nano-dots as well as nano-wires and deduce some rules which should facilitate the design of such novel polymer nano-composites. Finally we suggest a new mechanism to move nano-objects on the surface of diblock copolymer brushes.