Showing papers by "Emmanuel P. Giannelis published in 2007"

Compatibilizing Poly(vinylidene fluoride)/Nylon-6 Blends with Nanoclay

Abstract: Blends of poly(vinylidene fluoride)/nylon-6 (PVDF/N6) 30:70 were melt compounded with various organoclays directly or sequentially. The morphology, thermal, and mechanical properties of the blend nanocomposites were investigated. It was determined that the degree of compatibilization induced by the nanoclay particles was dependent on the location of the particles and the degree of clay dispersion. The blend nanocomposite with the best mechanical properties had good dispersion of particles throughout the matrix (N6) and at the PVDF/N6 interface. In this blend nanocomposite, the coalescence of PVDF domains was prevented, and the crystallization of the PVDF domains was suppressed, ultimately creating a blend nanocomposite that is stiffer, stronger, and tougher than the blend without nanoparticles.

Magnetic resonance in nanoparticles: between ferro- and paramagnetism

Abstract: Magnetic nanoparticles of γ -Fe2O3 coated with organic molecules and suspended in liquid and solid matrices, as well as non-diluted magnetic fluid, have been studied by electron magnetic resonance (EMR) at 77‐380 K. Slightly asymmetric spectra observed at room temperature become much broader and symmetric, and shift to lower fields upon cooling. An additional narrow spectral component (with a line-width of 30 G) is found in diluted samples; its magnitude obeys the Arrhenius law with an activation temperature of about 850 K. The longitudinal spin-relaxation time, T1 ≈ 10 ns, is determined by a specially developed modulation method. The angular dependence of the EMR signal position in field-freezing samples points to substantial alignment, suggesting the formation of dipolar-coupled aggregates. The shift and broadening of the spectrum upon cooling are assigned to the effect of the surface-related anisotropy. To describe the overall spectral shape, the ‘quantization’ model is used which includes summation of resonance transitions over the whole energy spectrum of a nanoparticle considered as a giant exchange cluster. This approach, supplemented with some phenomenological assumptions, provides satisfactory agreement with the experimental data. (Some figures in this article are in colour only in the electronic version)

Mechanism of heat transport in nanofluids

Abstract: We have calculated thermal conductivity of alumina nanofluids (with water and ethylene glycol as base fluids) using temperature as well as concentration-dependent viscosity, η. The temperature profile of η is obtained using Gaussian fit to the available experimental data. In the model, the interfacial resistance effects are incorporated through a phenomenological parameter α. The micro-convection of the alumina nanoparticle (diameter less than 100 nm) is included through Reynolds and Prandtl numbers. The model is further improved by explicitly incorporating the thermal conductivity of the nanolayer surrounding the nanoparticles. Using this improved model, thermal conductivity of copper nanofluid is calculated. These calculations capture the particle concentration-dependent thermal conductivity and predict the dependence of the thermal conductivity on the size of the nanoparticle. These studies are significant to understand the underlying processes of heat transport in nanofluids and are crucial to design superior coolants of next generation.

Quasielastic neutron scattering of poly(methyl phenyl siloxane) in the bulk and under severe confinement

Abstract: Quasielastic neutron scattering was utilized to investigate the influence of confinement on polymer dynamics. Poly(methyl phenyl siloxane) chains were studied in the bulk as well as severely confined within the ∼1–2nm interlayer spacing of intercalated polymer/layered organosilicate nanohybrids. The temperature dependence of the energy resolved elastic scattering measurements for the homopolymer and the nanocomposites exhibit two distinct relaxation steps: one due to the methyl group rotation and one that corresponds to the phenyl ring flip and the segmental motion. Quasielastic incoherent measurements show that the very local process of methyl rotation is insensitive to the polymer glass transition temperature and exhibits a wavevector independent relaxation time and a low activation energy, whereas it is not affected at all by the confinement. At temperatures just above the calorimetric glass transition temperature, the observed motion is the phenyl ring motion, whereas the segmental motion is clearly i...

Single-shot temporal coherence measurements of random lasing media

Abstract: A new method, to our knowledge, is proposed that enables single-shot measurements of the temporal coherence properties of pulsed laser sources. By modification of a Michelson interferometer, two replicas of the source are formed. Owing to the symmetry of the configuration, the optical path difference and, consequently, the visibility of the resulting interference fringes are varied over one dimension. This effectively replaces the mechanical scanning performed in a typical interferometer and thereby provides a direct measurement of the temporal coherence of a single pulse. Our method is successfully applied to the study of the single-shot temporal coherence of a Rhodamine 6G-ZnO-poly(methyl methacrylate) random laser system.

Toxicity and biomedical imaging of layered nanohybrids in the mouse.

Abstract: Layered nanohybrids (LNH) are a promising nonviral system allowing controlled drug and DNA delivery. In order to test the toxicity of LNH consisting of a magnesium/aluminum core, mice were subjected to subcutaneous, intraperitoneal, and intravenous injections of these nanoparticle sa t three doses. Intravenous injections resulted in 8% (1 out of 12) lethality at doses 100 µl and 200 µ lo f6.96 × 10 −4 M solution, while all mice survived after LNH administration by any other routes. Histopathological alterations were limited to mild localized inflammatory lesions in the lungs and the dermis after intravenous and subcutaneous administration, respectively. LNH labeled with Lucifer Yellow were readily detectable in both locations by fluorescent microscopy. To test their potential for intravital imaging, LNH-Lucifer Yellow were injected into the ovarian bursa and successfully visualized by multiphoton microscopy within the ovarian surface epithelial cells. In similar experiments, the ovary and the ovarian bursa were readily detectable by magnetic resonance imaging after administration of modified LNH, where aluminum was substituted for gadolinium. Taken together, these results demonstrate minimal in vivo toxicity of LNH and illuminate their potential as multifunctional nanoscale particles suitable for combination of intravital biomedical imaging with controlled drug release.

NMR and spin relaxation in systems with magnetic nanoparticles.

Abstract: The 1H NMR spectra and spin dynamics of the host systems have been studied in liquid and solid suspensions of γ-Fe2O3 nanoparticles. Significant broadening of 1H NMR spectra and growing relaxation rates were observed with increased concentration of nanoparticles in the liquid systems, with the relation T1/T2 depending on the particular host. Solid systems demonstrate inhomogeneous broadening of the spectra and practically no dependence of T1 upon the nanoparticle concentration. We explain the experimental results taking into account the predomination of self-diffusion as a source of the relaxation in liquid suspensions, and estimate effective parameters of relaxation in the systems under study.

Effect of magnetic nanoparticles to NMR and nuclear spin relaxation in liquid and solid hosts

Abstract: The H1 NMR spectra and spin dynamics of the host system in liquid and solid suspensions of γ-Fe2O3 nanoparticles are reported. Significant line broadening of H1 NMR spectra and growing relaxation rates were observed with increased concentration of nanoparticles in liquid systems, with the relation T1∕T2 depending on the particular host. Solid systems demonstrate inhomogeneous broadening of the spectra depending on the nanoparticle concentration and practically no dependence of T1 upon the nanoparticle concentration. In variable temperature experiments, significant increase in the relaxation rates was observed in the liquid systems. The experimental results are explained in terms of the self-diffusion as a predominating source of the spin-lattice relaxation. The effective radius of relaxation in the systems in study is estimated.

Group III nitride coatings and methods

Abstract: The invention provides a composition that is a dispersion made from a Group III nitride, a solvent system, and a dispersant. The dispersion can be used to prepare Group III nitride thin films on a wide range of substrates, for example, glass, silicon, silicon dioxide, silicon nitride, silicon carbide, aluminum nitride, sapphire, and organic polymers. The particle size of the Group III nitride used for producing the thin films can be controlled by adjusting centrifugation of the dispersion and selecting a desired layer of supernatant. The dispersant can be removed from the thin films by calcination. The Group III nitride can contain a dopant. Doped Group III nitride thin films can emit visible light upon irradiation. Green, red, and yellow light emissions result from irradiating erbium-, europium-, and cerium-doped gallium nitride, respectively.

Random laser action in ZnO nanohybrids

Abstract: A series of studies that investigate the influence of pump pulse duration and sample temperature on the random laser efficiency are presented along with coherence length measurements (Papadakis et al. 2007) on selected samples. Nanocomposite fabrication issues and pumping conditions are discussed in the context of performance optimization and potential use of such materials in future light emission devices.