Self-directed self-assembly of nanoparticle/copolymer mixtures

The organization of inorganic nanostructures within self-assembled organic or biological templates(1-11) is receiving the attention of scientists interested in developing functional hybrid materials. Previous efforts have concentrated on using such scaffolds(7,9,12) to spatially arrange nanoscopic elements as a strategy for tailoring the electrical, magnetic or photonic properties(8) (- 11,13 - 16) of the material. Recent theoretical arguments(16 - 18) have suggested that synergistic interactions between self-organizing particles and a self-assembling matrix material can lead to hierarchically ordered structures. Here we show that mixtures of diblock copolymers and either cadmium selenide- or ferritin-based nanoparticles exhibit cooperative, coupled self-assembly on the nanoscale. In thin films, the copolymers assemble into cylindrical domains, which dictate the spatial distribution of the nanoparticles; segregation of the particles to the interfaces mediates interfacial interactions and orients the copolymer domains normal to the surface, even when one of the blocks is strongly attracted to the substrate. Organization of both the polymeric and particulate entities is thus achieved without the use of external fields(10,19), opening a simple and general route for fabrication of nanostructured materials with hierarchical order.