Nanoscale Phase Separation in Mixed Poly(tert-butyl acrylate)/Polystyrene Brushes on Silica Nanoparticles under Equilibrium Melt Conditions

摘要

Mixed homopolymer brushes,composed of two chemically distinct polymer chains randomly or alternately immobilized by one end via a covalent bond on a solid surface with high grafting densities,represent a new class of stimuli-responsive materials.It has been a long-standing fundamental issue in polymer science whether symmetric mixed homopolymer brushes on a flat substrate microphase separate laterally or vertically under equilibrium melt conditions.Theoretically,Marko and Witten predicted a lateral phase separation,forming a "rippled" state,for symmetric mixed brushes on a flat substrate.The transition is expected to occur at a critical molecular weight 2.27 times that for the same homopolymers in a simple blend at its demixing threshold,and the spatial period of the pattern is predicted to be on the order of polymer chain root-mean-square end-to-end distance.However,it is unknown what pattern (random,stripe,or checkerboard) would form on a flat substrate and how the curvature would affect the pattern if the substrate is curved.