Nanoparticle encapsulation in thin film micellar structures: a physical method for functional materials design

We investigate the confinement of gold nanoparticles, onto which poly(2-vinylpyridine) (P2VP) are end-tethered, within diblock copolymer polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) micelles in a polystyrene (PS) host. The micellar nanocomposites were prepared by spin casting mixtures of the nanoparticles, the copolymer and the homopolymer chains onto a substrate, to form films approximately 110 nm thick. The samples were then annealed above the glass transitions of the polymers, resulting in the formation of spherical micelles, composed of inner cores of the P2VP segments and outer coronas comprising the PS blocks, throughout the PS homopolymer thin film host. All nanoparticles were encapsulated within micelle cores; on average each micelle contains one, or no, nanoparticle. The micelles exhibited a strong tendency to self-organize at interfaces when the PS homopolymer chain length is large compared to the PS corona chain length; they otherwise remain distributed throughout the film. In comparison to pure PS-b-P2VP/PS blends, the nanoparticle/PS-bP2VP/ PS blends contain a higher density of, on average, smaller micelles. This sample fabrication procedure is straightforward and compliments the current toolbox used to create functional materials from block copolymer-nanoparticle systems.