Vertical Block Copolymer Cylinder-Nanorod Self-Assembly
The properties of polymer nanocomposites (PNCs) depend on the position and orientation of nanoparticles in the polymer matrix. Improved control over nanoparticle position and orientation in PNCs would result in PNCs with improved properties. A powerful approach to controlling nanoparticle position and orientation in PNCs is nanoparticle-block copolymer (NP-BCP) self-assembly. NP-BCP self-assembly with spherical nanoparticles has been extensively studied. However, NP-BCP self-assembly with anisotropic nanoparticles is less well understood. In this work we study the position and orientation of nanorods in self-assembled nanorod-BCP nanocomposite films. More specifically we study films consisting of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and gold nanorods (AuNRs) functionalized with P2VP. When the films are solvent annealed the PS-b-P2VP assumes a morphology of vertical P2VP cylinders in a PS matrix. Relatively short AuNRs are found to localize at the base of the vertical P2VP cylinders with their axis parallel to the substrate. Simulations showed that the AuNRs relieved chain stretching at the base of the cylinders. Studies were done with longer 70 nm and 101 nm long nanorods. The 70 nm nanorods were distributed between three states at the film surface. The three states were the bridging state, the centered state and the vertical state. The bridging state is where the AuNR is embedded in the film surface, the AuNR long axis is parallel to the film surface and each end of the AuNR is at the top of nearest neighbor P2VP cylinders. The centered state is where the AuNR is embedded in the film surface, the AuNR axis is parallel to the film surface, and the AuNR is centered over a single vertical P2VP cylinder. The vertical state is where the AuNR is localized within a vertical P2VP cylinder, is vertically oriented and has its tip at the film surface. The 101 nm long AuNRs were distributed between the bridging and vertical states at the film surface. The experimental results were compared to hybrid particle-field theory (HPFT) calculations of the system free energy. Further, HPFT simulations were used to understand the block copolymer morphology when a 101 nm long AuNR was in the bridging state.
Materials science|Nanoscience|Polymer chemistry
Rasin, Boris, "Vertical Block Copolymer Cylinder-Nanorod Self-Assembly" (2019). Dissertations available from ProQuest. AAI27547105.