Showing papers by "Richard W. Siegel published in 2003"

Selective Attachment of Gold Nanoparticles to Nitrogen-Doped Carbon Nanotubes

Abstract: Gold nanoparticles were selectively attached to chemically functionalized surface sites on nitrogen-doped carbon (CNx) nanotubes. A cationic polyelectrolyte was adsorbed on the surface of the nanotubes by electrostatic interaction between carboxyl groups on the chemically oxidized nanotube surface and polyelectrolyte chains. Negatively charged 10 nm gold nanoparticles from a gold colloid suspension were subsequently anchored to the surface of the nanotubes through the electrostatic interaction between the polyelectrolyte and the nanoparticles. This approach provides an efficient method to attach other nanostructures to carbon nanotubes and can be used as an illustrative detection of the functional groups on carbon nanotube surfaces.

Rescaled electrical properties of ZnO/low density polyethylene nanocomposites

Abstract: ZnO/low density polyethylene (LDPE) nanocomposites were prepared using melt mixing with good dispersion of the ZnO nanoparticles. The electrical properties (dc resistivity and breakdown strength) of the composite with various concentrations of ZnO up to the percolation limit were measured and compared to the corresponding electrical properties of submicron ZnO filled LDPE. It was observed that the nanocomposites exhibited a lower percolation limit and a slower decrease in resistivity with filler concentration compared to the conventional composite. The dielectric breakdown strength was also found to be higher for the nanocomposite at high filler concentration.

Polymer crystalline structure and morphology changes in nylon‐6/ZnO nanocomposites

Abstract: The influence of ZnO nanoparticles on the crystalline structures of nylon-6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide-angle X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ-crystal-line form in nylon-6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon-6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon-6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon-6 are ascribed to the reorganization of imperfect crystals.

Preparation and structure investigation of nanoparticle-assembled titanium dioxide microtubes

Abstract: Nanoparticle-assembled capped TiO2 microtubes were synthesized by means of a recently discovered freeze-drying method. Most tubes are about 1 μm in diameter and have a high aspect ratio. The resulting structure was observed using field emission scanning electron microscopy and transmission electron microscopy. The crystal structure and chemical nature of the nanoparticle constituents and the resulting structures were investigated by x-ray diffraction, selected area energy dispersive x-ray spectroscopy, and Raman spectroscopy. The formation of the observed TiO2 microtubes occurs through the physical rearrangement or self-organization of nanoparticles, most likely driven by capillarity and aided by hydrogen bonding between nanoparticles and the water molecules during freeze-drying.

ZnO/PMMA thin film nanocomposites for optical coatings

Abstract: The optical properties of nano-scale zinc oxide/PMMA composites were investigated. Films were produced by spin coating and cast coating dispersions of nanoparticle/PMMA organic solutions. This allows for the preparation of nanocomposite films with controlled thickness containing up to 22 vol. % homogeneously dispersed nanofillers. It was found that the refractive index of the composite films scaled linearly with volume fraction of nanofillers. The films were transparent in the visible light range and strongly absorbing in the UV range. When the films were loaded with a high content of such semiconductor nanoparticles, the surface resistivity decreased enough for the coatings to be used for antistatic applications.

Tubular microstructures via controlled nanoparticle assembly

Abstract: A process for producing microtubes from nanoparticles includes forming a dispersion of the nanoparticles in a liquid phase and freeze-drying the dispersion to produce microtubes. The nanoparticles have surface functionality capable of self-bonding and bonding with the liquid phase during freeze-drying, particularly surface hydroxy functionality.