Polymer nanocomposites (PNCs), prepared by incorporating nanoparticles within a polymer host, generally exhibit properties that differ significantly from those of the host, even with small amounts of nanoparticles. A significant challenge is how to tailor the properties of these materials for applications (structural and biomedical to optoelectronic), because PNCs derive their properties from a collective and complex range of entropic and enthalpic interactions. Here, we show that PNCs, prepared from athermal mixtures of polymer-chain-grafted gold nanoparticles and unentangled polymer chains, may exhibit increases or decreases in their relaxation dynamics, and viscosity, by over an order of magnitude through control of nanoparticle concentration, nanoparticle size, grafting density and grafting chain degree of polymerization. In addition, we show how the glass transition may also be tailored by up to 10 degrees with the addition of less than 1.0 wt% nanoparticles to the polymer host.

We show that thin film star-shaped macromolecules exhibit significant differences in their average vitrification behavior, in both magnitude and thickness dependence, from their linear analogs. This behavior is dictated by a combination of their functionality and arm length. Additionally, the glass transition temperature at the free surface of a star-shaped molecule film may be higher than that of the interior, in contrast to their linear analogs where the opposite is true. These findings have implications for other properties, due largely to the origins, entropic, of this behavior.

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The physical properties of thin polymer films are often thickness, h, dependent, influenced by confinement and by interfacial interactions between the chains and the external interfaces. We show that the magnitude and film thickness dependence of the average glass transition temperature, T g, of the polystyrene−silicon oxide (PS/SiO x /Si) system are influenced appreciably with the addition of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymers. The T g can be “tailored” to increase, or decrease, with decreasing h or to remain independent of h. T g shifts of as much of 35 °C are obtained for films of h ≈ 20 nm. Additionally, we report that the critical micelle concentration, φcmc, of the copolymer in thin films is considerably larger than for the bulk; specifically, micelles form only beyond a critical film thickness, determined by the size of the chains and by the number of chains in the system. The h dependence of T g is not influenced by the ϕcmc or by the number of micelles in this system.