Encapsulation and one-dimensional alignment of nanomaterials within cross-linked block copolymer micelles

Assembly of amphiphilic block copolymers and nanomaterials is described in this thesis. Amphiphilic block copolymers can be spontaneously assembled and crosslinked around inorganic nanomaterials to form permanent core-shell nanostructures without the need for covalent attachment of the polymer to the particle. Single-walled carbon nanotubes (SWNTs) and Au nanoparticles were encapsulated within micelles made from amphiphilic poly(styrene- block-acrylic acid) (PS-b-PAA) or poly(methylmethacrylate- block-acrylic acid) (PMMA-b-PAA) copolymers. Encapsulation was accomplished by simultaneously desolvating the hydrophobic or the hydrophobically modified nanomaterials and the hydrophobic polymer block to localize the nanomaterial within the micelle core. The hydrophilic, outer shells of these micelles were then chemically crosslinked with a difunctional linker molecule. The resulting core-shell architectures were extensively characterized by atomic force microscopy (AFM), electron microscopy (TEM, SEM), dark-field optical microscopy and optical spectroscopy. The structure and physical properties of these nanomaterials were precisely determined by the characteristics of the self-assembled components. For Au nanoparticles, the thickness of shell can be predicted from theoretical models of polymer adsorption onto highly curved surfaces, and controlled by varying the ratio of polymer to available nanoparticle surface area. The thermal conductance measurement of the encapsulated Au nanoparticles shows that the permeability of polymer shells can be easily modulated by organic co-solvents. We also found that the encapsulated nanomaterials can be spontaneously assembled into 1D chains by a morphological transition of polymer micelles from sphere to worm-like structure. Electron microscopy demonstrated that the structure of the resulting 1D chain was precisely dictated by the characteristics of the encapsulated nanomaterials.; Because the crosslinked micelle shells are topologically linked to nanoparticles rather than chemically bound, we suggest that the encapsulation approach to core-shell nanostructures might be used to add polymer shells to nanomaterials that lack effective surface chemistries.