Showing papers by "Richard W. Siegel published in 2011"
TL;DR: Al-containing ZnO nanocomposites are reported with up to a factor of 20 lower κ(L) than non-nanostructured ZNO, while retaining bulklike α and σ, and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.
Abstract: ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κL. Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κL than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl2O4 nanoprecipitates presages ultralow κ ∼ 2 Wm −1 K–1 at 1000 K. The high α∼ −300 μV K–1 and high σ ∼ 1–104 Ω–1 m–1 result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ∼ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for appl...
412 citations
TL;DR: In this article, a transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto anatase TiO2 nanoparticles via a combination of phosphate ligand engineering and alkyne-azide "click" chemistry.
Abstract: Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto anatase TiO2 nanoparticlesvia a combination of phosphate ligand engineering and alkyne-azide “click” chemistry. Highly crystalline TiO2 nanoparticles with 5 nm diameter were synthesized by a solvothermal method and used as high refractive index filler. The synthesized phosphate-azide ligand anchors strongly onto the TiO2 nanoparticle surface and the azide end group allows for attachment of poly(glycidyl methacrylate) (PGMA) polymer chains through an alkyne-azide “click” reaction. The refractive index of the composite material increased linearly from 1.5 up to 1.8 by increasing the loading of TiO2 particles to 30 vol % (60 wt %). UV-vis spectra show that the nanocomposites exhibited a transparency around 90% throughout the visible light range. It was also found that the PGMA-grafted TiO2 nanoparticles can be well dispersed into a commercial epoxy resin, forming transparent high refractive index TiO2-epxoy nanocomposites.
274 citations
TL;DR: It is clear that AuNP morphology does affect adsorbed protein structure; a better understanding of these differences will be essential to engineer fully functional nanobioconjugates.
261 citations
TL;DR: In this article, an azido-phosphate ligand was synthesized and used to exchange with oleic acid on the ITO surface, allowing for the grafting of epoxy resin compatible PGMA polymer chains via Cu(I) catalyzed alkyne-azide chemistry.
Abstract: Visibly highly transparent indium tin oxide (ITO)/epoxy nanocomposites were prepared by dispersing polyglycidyl methacrylate (PGMA) grafted ITO nanoparticles into a commercial epoxy resin. The oleic acid stabilized, highly crystalline, and near monodisperse ITO nanoparticles were synthesized via a nonaqueous synthetic route with multigram batch quantities. An azido–phosphate ligand was synthesized and used to exchange with oleic acid on the ITO surface. The azide terminal group allows for the grafting of epoxy resin compatible PGMA polymer chains via Cu(I) catalyzed alkyne–azide “click” chemistry. Transmission electron microscopy (TEM) observation shows that PGMA grafted ITO particles were homogeneously dispersed within the epoxy matrix. Optical properties of ITO/epoxy nanocomposites with different ITO concentrations were studied with an ultraviolet–visible-near-infrared (UV–vis-NIR) spectrometer. All the ITO/epoxy nanocomposites show more than 90% optical transparency in the visible light range and absor...
122 citations
Journal Article•
25 citations
Patent•
25 Aug 2011TL;DR: In this article, the porosity of the nanoporous film can be tuned during fabrication to a desired value by adjusting the deposition conditions, which can be used for fabrication of conformable coatings.
Abstract: The invention is directed to a composite polymer/nanoporous film system and methods of fabrication of tunable nanoporous coatings on flexible polymer substrates. The porosity of the nanoporous film can be tuned during fabrication to a desired value by adjusting the deposition conditions. Experiments show that SiO 2 coatings with tunable porosity fabricated by oblique-angle electron beam deposition can be deposited on polymer substrates. These conformable coatings have many applications, including in the field of optics where the ability to fabricate tunable refractive index coatings on a variety of materials and shapes is of great importance.
17 citations
TL;DR: It is demonstrated that biomaterial substrate topography, such as ceramic grain size, affects mesenchymal stem cell differentiation in a size-dependent but, non-linear, manner.
11 citations
TL;DR: In this paper, a transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto TiO 2 nanoparticles, which had a transparency of more than 90% in the visible light range.
Abstract: Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto TiO 2 nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to prepare poly(methyl methacrylate) (PMMA) polymer brushes grafted from TiO 2 nanoparticles. The refractive index of the hybrid material increased from 1.49 for neat PMMA to 1.6 by increasing the loading of TiO 2 to 40 weight percent. UV-vis spectra showed that grafted particles had a transparency of more than 90% in the visible light range. The hybrid particles can be processed into transparent, high refractive index coatings and self-standing films. The grafted TiO 2 nanoparticles can also be easily dispersed into a polymer matrix forming thick, robust transparent polymer nanocomposites.
7 citations