| Polymer nanocomposites (PNCs), polymer hosts into which nano-scale fillers are incorporated, are a technologically important class of materials, with diverse applications: optoelectronic devices, coatings, lithographic tools, membranes and stimulus-responsive systems. Understanding, controlling and optimizing the properties of these materials continue to pose significant technical challenges. Control of the spatial distribution of the nanofillers within the polymer hosts remains one of the challenges due to complex entropic and enthalpic interactions.;Many of the applications of PNCs require them to perform in geometrically confined environments, such as thin films, where interactions between the constituents of the PNC and interfaces are important. The role of the interfaces is sometimes unclear; in some cases the presence of the interfaces can change the morphology and hence the properties/performance of the PNC.;Our research is aimed at gaining control of the structure and nano-scale morphology of thin film PNCs and understanding the structure-property relationships. Our goal is to design PNCs with tailored morphologies and desired properties for specific applications. A series of topics are examined.;First we introduce the design rules of thin film PNCs by investigating the equilibrium structure of polymer-tethered metal nanoparticles/polymer composites. Specifically, the morphologies of thin film blends of polystyrene (PS)-brush coated Au nanoparticles with tetramethyl bisphenol-A polycarbonate (TMPC) were investigated. The role of entropic and enthalpic interactions towards determining the structure of thin film polymer/polymer-tethered nanoparticle systems is examined.;Following that we apply the rules to the design of a series of PNCs with tailored fluorescence properties using chain-grafted Au nanoparticle/poly[2-methoxy-5(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) mixtures. We achieved control of the Au nanoparticle distribution within MEH-PPV by manipulating the enthalpic and entropic interactions between the grafted brush layers and the host chains. Further, the fluorescence of these Au/MEH-PPV nanocomposite thin films may be "tailored" by as much as an order of magnitude, through changes in the nanoparticle distribution, brush length and nanoparticle size.;Lastly, we compare different tethered structures (nanoparticles vs diblock copolymer) in thin film PNCs. The roles of entropy and enthalpy in the micelle formation and surface adsorption of diblock copolymers in thin film homopolymer melts are examined. |
