Search

Cadmium selenide nanoparticles are found to diffuse approximately 200 times faster in a polymeric liquid than predicted by the Stokes−Einstein relation. This remarkable behavior is hypothesized to be due to the nanoparticles being smaller than the entanglement mesh to create a frictional drag that does not follow continuum expectations, in line with a theoretical calculation presented before. This is one of the first demonstrations of X-ray photo correlation spectroscopy applied to polymeric liquids, which we use to explain the simultaneous 60% viscosity reduction of the mixture through a proposed constraint release mechanism. [ABSTRACT FROM AUTHOR]

We show it is possible to assemble nanoparticle−polymer layers in a controllable manner dictated by the difference in nano-object morphology and dielectric properties. A thin (10−100 nm) layer of the two components is spin coated onto a solid substrate and the system thermally aged to activate a cross-linking process between polymer molecules. The nanoparticles segregate to the solid substrate prior to complete cross-linking if entropic forces are dominant or to the air interface if dielectric (surface energy) forces are properly tuned. Subsequent layers are then spin coated onto the layer below, and the process is repeated to create layered structures with nanometer accuracy useful for tandem solar cells, sensors, optical coatings, etc. Unlike other self-assembly techniques the layer thicknesses are dictated by the spin coating conditions and relative concentration of the two components. [ABSTRACT FROM AUTHOR]

It is demonstrated that nanocomposites exhibiting reduced viscosity and multifunctional performance enhancements may be fabricated using simple processing procedures. These behaviors are elucidated by analysis of the effects of dispersed organic (fullerene) nanoparticles and inorganic (magnetite) nanoparticles on the behavior of polystyrene, demonstrating that simple spherical nanoparticles can induce a range of unexpected behavior due to nanoscale effects. In general, multifunctional performance improvements including enhanced mechanical, electrical, magnetic and thermal degradation properties as well as reduced viscosity are promoted when simple design guidelines are followed. These guidelines are tabulated. [ABSTRACT FROM AUTHOR]

Diels−Alder (DA) chemistry is increasing popular due to its simplicity and efficiency; however, one concept that has yet to be thoroughly explored is incorporation of DA linkages within materials for the development of polymeric phase change materials. It is well established that the retro-DA reaction results in a large endotherm, which could be a potential energy sink for phase change materials. Hydroxyl-terminated polybutadiene (HTPB) was selected as a prepolymer and modified with different DA linkages. Cured materials were prepared upon addition of diisocyanates and their physical properties of the cured elastomers were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and rheological testing. The resulting thermally responsive HTPB (TR-HTPB) exhibited the ability to absorb energy and flow at elevated temperatures. Furthermore, they displayed unusual responses to repeated thermal cycling, including changes in thermal absorption and rheological characteristics. [ABSTRACT FROM AUTHOR]

A new synthetic approach to the preparation of intramolecularly collapsed nanoparticles under mild, room temperature conditions has been developed from commercially available vinyl monomers. Reaction of isocyanate functionalized linear copolymers with a diamine in dilute solution leads to the efficient formation of nanoparticles where the diameter of the nanoparticle can be varied by controlling both the molecular weight and mole percentage of isocyanate repeat units. Physical properties for the intramolecularly collapsed nanoparticles were fully consistent with a three-dimensional structure and analysis of the collapse reaction revealed that approximately 75% of the isocyanate groups along the backbone underwent cross-linking with 25% being available for further reaction with monofunctional amines. This stepwise consumption of the isocyanates allows the chemical and physical properties of the nanoparticles to be further tuned and significantly opens up the range of nanoparticles that can be prepared using this mild and highly efficient chemistry. [ABSTRACT FROM AUTHOR]

Polymandelide, an aryl analogue of polylactide, was synthesized by the ring-opening polymerization of mandelide, the cyclic dimer of mandelic acid. The poor solubility of rac-mandelide limited the synthesis of polymandelide via solution polymerization, but polymerization of mandelide at 70 °C as a heterogeneous slurry in acetonitrile yielded first-order kinetic plots and polydispersities <1.2. High molecular weight polymer prepared by melt polymerizations at T> 150 °C exhibit properties that mimic those of polystyrene. Polymandelide is a glassy amorphous polymer with a Tgof 100 °C, with rheological properties comparable to polystyrene, and thermal gravimetric analyses under nitrogen show that the polymer is stable to ∼300 °C. Racemization during polymerization precluded formation of a crystalline polymer. Degradation of polymandelide in pH 7.4 buffer at 55 °C is consistent with a bulk erosion model and, due to its high Tg, proceeds at ∼1/100 the rate of polylactide under similar conditions. [ABSTRACT FROM AUTHOR]

A supramolecular elastomer comprising a blend of a pyrenyl-tweezer-ended polyamide intercalating with a chain-folding polyimide shows near-quantitative thermal healability. It also exhibits greatly enhanced toughness relative to an analogous system in which the polyamide end-groups are simple pyrenyl residues, reflecting the increased association constant between the two complementary binding motifs. [ABSTRACT FROM AUTHOR]