<p>This study reports on the changes in the structural properties of a tungsten-filament when exposed to a methane / hydrogen ambient for different durations at various filament-temperatures.</p>

This thesis presents models and simulations of dielectrophoretic separation of micro and nano particles. The fluid dynamics involved and the dielectric properties of water inside single-walled carbon nanotube are studied as well. Based on the effective dipole moment method, the particle dynamic model focuses on the translational motions of micro particles. The hydrodynamic force between the particles and the particle-particle electrostatic interactions are considered as well. By comparing the dimensionless parameters, the dominating force can be determined. Based on a simplified version of the particle dynamic model, two numerical simulations are carried out to predict the efficiency of dielectrophoretic separation of micro size particles. The first calculation suggests a strategy to improve the trapping efficiency of E.coli bacteria by applying superimposed AC electric fields. The second calculation discusses the concept of mobility and improves the separation rate of particles by a multi-step trapping-releasing dielectrophoresis strategy. The model is extended down scale to calculate the separation of metallic and semiconducting single-walled carbon nanotubes by the modified effective dipole moment method for prolate ellipsoids. The steeply changed gradient of electric field results in the local joule heating therefore creates gradient of dielectric properties in the solution. As a result, certain pattern of fluid flow with a considerable strength is created and affects the motion of carbon nanotubes especially close to the electrode gap, which indicates that the so-called electrothermal flow should be considered in designing the experiment to separate single-walled carbon canotubes. When the length scale of particles is comparable to that of the electrodes, the calculation of dielectrophoretic force by the effective dipole moment is considered not to be accurate since only the electric field in the center point is taken into account. Hence in the thesis a new method based on distributed induced charge is suggested. By approximating a straight slender body as a prolate ellipsoid, the electric field of multiple points along the centerline are all considered in the calculation and the interaction between particles could be concurrently taken care. This method is expected to be an improved method to calculate the dielectrophoretic force of rod-like virus, DNA, nanowires and carbon nanotubes. The dielectric property of water confined in carbon nanotubes is expected to be dramatically different from that of bulk water. The thesis also contains a molecular dynamics study to reveal the difference also a dependence on the diameter of carbon nanotubes. The results show that along the axial direction, both the static permittivity and the relaxation time are larger than the isotropic bulk water, and in the cross-section plane it is opposite. When the radius of the carbon nanotubes increases, the properties of water inside become closer to the bulk water. / QC 20100820

In this work, gadolinium-based carbon nanocapsules are developed as a novel nanotechnology that addresses the shortcomings of current diagnostic and therapeutic methods of stem cell-based cardiomyoplasty. With cardiovascular disease (CVD) responsible for approximately 30% of deaths worldwide, the growing need for improved cardiomyoplasty has spurred efforts in nanomedicine to develop innovative techniques to enhance the therapeutic retention and diagnostic tracking of transplanted cells. Having previously been demonstrated as a high-performance T1-weighted magnetic resonance imaging (MRI) contrast agent, Gadonanotubes (GNTs) are shown for the first time to intracellularly label pig bone marrow-derived mesenchymal stem cells (MSCs). Without the use of a transfection agent, micromolar concentrations of GNTs deliver up to 10^9 Gd(III) ions per cell, allowing for MSCs to be visualized in a 1.5 T clinical MRI scanner. The cellular response to the intracellular incorporation of GNTs is also assessed, revealing that GNTs do not compromise the viability, differentiation potential, or phenotype characteristics of the MSCs. However, it is also found that GNT-labeled MSCs exhibit a decreased response to select cell adhesion proteins and experience a non-apoptotic, non-proliferative cell cycle arrest, from which the cells recover 48 h after GNT internalization. In tandem with developing GNTs as a new stem cell diagnostic agent, this current work also explores for the first time the therapeutic application of the magnetically-active GNTs as a magnetic facilitator to increase the retention of transplanted stem cells during cardiomyoplasty. In vitro flow chamber assays, ex vivo perfusion experiments, and in vivo porcine injection procedures all demonstrate the increased magnetic-assisted retention of GNT-labeled MSCs in the presence of an external magnetic field. These studies prove that GNTs are a powerful ‘theranostic’ agent that provides a novel platform to simultaneously monitor and improve the therapeutic nature of stem cells for the treatment of CVD. It is expected that this new nanotechnology will further catalyze the development of cellular cardiomyoplasty and other stem cell-based therapies for the prevention, detection, and treatment of human diseases.

Existing growth methods produce single-walled carbon nanotubes (SWCNTs) with a range of structures and electronic properties, but many potential applications require pure nanotube samples. Density gradient ultracentrifugation (DGU) has recently emerged as a technique for sorting as-grown mixtures of single-walled nanotubes into their distinct ( n,m ) structural forms, but this approach has been limited to samples containing only a small number of nanotube structures, and has often required repeated DGU processing. For the first time, it has been shown that the use of tailored nonlinear density gradient ultracentrifugation (NDGU) can significantly improve DGU separations. This new sorting process readily separated highly polydisperse samples of SWCNTs grown by the HiPco method in a single step to give fractions enriched in any of ten different ( n,m ) species. In addition, minor variants of the method allowed separation of the minor-image isomers (enantiomers) of seven ( n,m ) species. Optimization of this new approach was aided by the development of instrumentation that spectroscopically mapped nanotube contents inside undisturbed centrifuge tubes. Besides, sorted nanotube samples enabled the discovery of novel oxygen-doped SWCNTs with remarkable photophysical properties. Modified nanotube samples were produced using mild oxidation of SWCNTs with ozone followed by a photochemical conversion step that induced well-defined changes in emissive properties. As demonstrated for a set of ten separated SWCNT ( n,m ) structures, chemically altered nanotubes possess slightly lower band gap energies with correspondingly longer photoluminescence wavelengths. Treated samples showed distinct, structure-specific near-infrared fluorescence at wavelengths 10 to 15% longer than the pristine semiconducting SWCNTs. Quantum chemical modeling suggests that dopant sites harvest light energy absorbed in undoped nanotube regions by trapping mobile excitons. The oxygen-doped SWCNTs are much easier to detect and image in biological specimen than pristine SWCNTs because they give stronger near-IR emission and do not absorb at the shifted emission wavelength. This novel modification of SWCNT properties may lead to new optical and electronic applications, as it provides a way to change optical band gaps in whole nanotubes or in selected sections.

This study presents near-field electrospinning (NFES) on flat and hollow cylindrical process to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF)/ multi-walled carbon nanotube (MWCNT) piezoelectric nanofibers. Then the mechanical properties of fibers were measured. PVDF is a potential piezoelectric polymer material combining desirable mechanical, thermal, electrical properties with excellent chemical resistance. The existing researches mostly focused on piezoelectric thin film process. However, the research of characteristic about piezoelectric fiber is little. The methods of measurement of the mechanical properties (Young¡¦s modulus, hardness, and tensile strength¡Belongation) of the electrospun PVDF/MWCN composite nanofiber were carried out by using nano-indention test (MTS Nanoindenter Windows XP System) and tensile test (Microforce Testing System). By setting electric field (1¡Ñ107 V/m), rotating velocity (900 rpm) of the hollow cylindrical glass tube on a motion X-Y stage (2 mm/sec) and PVDF solution concentration (16 wt%), and MWCNT (0.03 wt%), in-situ electric poling, mechanical stretching and morphology of PVDF nanofiber were demonstrated. After the experiments of nano-indention test and tensile strength test, it is suggested that the good mechanical properties in NFES on cylindrical process. The results show that the mechanical properties of composite nanofiber are better than the conventional NFES process. The Young¡¦s modulus of 16% PVDF fiber prepared by cylindrical process is 0.89 GPa and hardness is 26.5 MPa. The mechanical properties were increased 56.2% and 49.4% after adding 0.03% of MWCNT, corresponding to 1.39 GPa and 39.6 MPa. The tensile strength was increased 32.7% and elongation at breaking point was increased 35% after adding 0.03% MWCNT.

The use of Multi-Walled Carbon Nanotubes (MWCNT) as solid sorbent in Matrix Solid-Phase Dispersion (MSPD) extraction and preconcentration method was presented to determine some commonly used organophosphorus insecticides/OPIs in honey samples using a Gas Chromatography Flame Ionization Detector (GC-FID). OPIs are poisonous compounds used to kill insects and rodents by affecting their nervous system. The limit of detections obtained after MSPD extraction were 7.0 ng/g for Malathion, Malaoxon and Fenitrothion and 33.3 ng/g for Isomalathion. The recovery of the insecticides from spiked honey, ranged from 83.6% to 103.3% with % RSD ranged from 9.8% to 12.3% (n=3). The correlation coefficient (R2) of the calibration data varied from 0.9945 to 0.9987. Standard addition method was utilized to examine matrix-induced effects on analyte peaks, and to demonstrate the efficiency of the method. The MSPD extraction was successfully applied for the analysis of four honey samples but no insecticide residues were detected.

The first part of this dissertation is an introduction describing a brief historical background of carbon nanotubes (CNTs) and their pseudo 1D structure responsible for many exotic electronic properties. The second part describes our experimental setup. The third part is about the growing of Multi-Walled Carbon Nanotubes (MWCNTs) by the chemical vapor deposition (CVD) method. Then the fourth part demonstrates a simple but reliable method to make firm contact junctions between MWCNTs and metals such as tungsten (W). The novel point of our method consists, after making a mechanical preliminary contact at a selected MWCNT, in applying a series of voltage pulses across the contact. Thin oxide layers that may form between the MWCNT and the W wire, are removed in steps by the resistive heating and electron impact during the application of each voltage pulse. Furthermore, this simple process of contact welding in steps does not bring about any permanent change in the electronic transport properties of the MWCNTs. The fifth part discusses our bending experiments. We apply a uniform and continuous bending to a selected MWCNT at room and liquid nitrogen temperatures to study the strain effect on the electrical transport in the MWCNT. There are a few published experimental works related to the bending deformation; however, this is the first study of electronic transport properties in continuous bending and releasing deformations. We observed a saturation behavior with the MWCNT and also found the bending deformation causing an anomalous change in the saturation behavior. In the sixth part we depict some interesting phenomena due to the stretching deformation of MWCNT, where we were able to propose a simple model for electron localization induced by the deformation. The last part deals with the formation of the "X-junction" between two MWCNTs. A strong X-junction can be formed simply by means of the e-beam inside the Scanning Electron Microscope (SEM). The X-junctions may form the basic elements of nano-electronic circuits such as various metal-insulator junctions, quantum dots, and similar devices. / text

The purpose of this thesis is to develop corotational beam elements for the nonlinear dynamic analyse of flexible beam structures. Whereas corotational beam elements in statics are well documented, the derivation of a corotational dynamic formulation is still an issue. In the first journal paper, an efficient dynamic corotational beam formulation is proposed for 2D analysis. The idea is to adopt the same corotational kinematic description in static and dynamic parts. The main novelty is to use cubic interpolations to derive both inertia terms and internal terms in order to capture correctly all inertia effects. This new formulation is compared with two classic formulations using constant Timoshenko and constant lumped mass matrices. In the second journal paper, several choices of parametrization and several time stepping methods are compared. To do so, four dynamic formulations are investigated. The corotational method is used to develop expressions of the internal terms, while the dynamic terms are formulated into a total Lagrangian context. Theoretical derivations as well as practical implementations are given in detail. Their numerical accuracy and computational efficiency are then compared. Moreover, four predictors and various possibilities to simplify the tangent inertia matrix are tested. In the third journal paper, a new consistent beam formulation is developed for 3D analysis. The novelty of the formulation lies in the use of the corotational framework to derive not only the internal force vector and the tangent stiffness matrix but also the inertia force vector and the tangent dynamic matrix. Cubic interpolations are adopted to formulate both inertia and internal local terms. In the derivation of the dynamic terms, an approximation for the local rotations is introduced and a concise expression for the global inertia force vector is obtained. Four numerical examples are considered to assess the performance of the new formulation against two other ones based on linear interpolations. Finally, in the fourth journal paper, the previous 3D corotational beam element is extended for the nonlinear dynamics of structures with thin-walled cross-section by introducing the warping deformations and the eccentricity of the shear center. This leads to additional terms in the expressions of the inertia force vector and the tangent dynamic matrix. The element has seven degrees of freedom at each node and cubic shape functions are used to interpolate local transversal displacements and axial rotations. The performance of the formulation is assessed through five examples and comparisons with Abaqus 3D-solid analyses. / <p>QC 20131017</p>

Unikaliomis savybėmis pasižyminčios anglinės nanostruktūros panaudojamos dangų ir plėvelių gamyboje, kurios pritaikomos nanoelektronikoje, biotechnologijoje ir kitose srityse. Šio darbo tikslas buvo susintetinti daugiasienius anglinius nanovamzdelius ir grafito oksidą, pagaminti ir ištirti jų dangas. Mūsų laboratorijoje daugiasieniai angliniai nanovamzdeliai buvo susintetinti cheminio nusodinimo iš garų fazės metodu. Susintetinto produkto valymui nuo katalizatoriaus priemaišų pirmą kartą buvo panaudoti CCl4 garai. Ištyrus CCl4 garais paveiktą medžiagą buvo pagrįstas šio valymo metodo efektyvumas. Grafito oksidas buvo gautas oksiduojant grafitą Hummers'o metodu. Anglinių nanovamzdelių dangos ant skirtingų pagrindų buvo pagamintos cheminio nusodinimo iš garų fazės metodu bei suformuotos panaudojant medžiagos vandenines suspensijas. Grafito oksido su Kongo raudonojo dažo priedu dangos ir plėvelės buvo pagamintos laboratorijoje sukurtu filtravimo į tirpalą metodu. Anglinių nanovamzdelių ir jų dangų tyrimo rezultatai parodė, kad dangų morfologija priklauso nuo sintezės sąlygų, o paviršiaus savybes nulemia prisijungusių funkcinių grupių pobūdis ir kiekis. Ištyrus grafito oksido plėveles ir dangas buvo nustatyta, kad Kongo raudonojo dažo priedas skatina kompaktiškesnių nanokompozitų susidarymą ir stiprina dangų bei plėvelių patvarumą. / Films and coatings of carbonaceous nanostructures are employed in nanoelectronics, biotechnology and other fields. The aim of the research was to synthesize multi-walled carbon nanotubes and graphite oxide and fabricate coatings thereof. Consequently, multi-walled carbon nanotubes and their coatings were synthesized by the catalytic chemical vapour deposition method. As-grown carbon nanotubes inevitably contain remains of metal catalyst particles. A method developed in the laboratory using CCl4 was successfully applied to remove the residual catalyst from the batch of synthesized carbon nanotubes. Simultaneously, graphite oxide was synthesized from graphite powder by Hummer's method. Coatings and films of carbonaceous nanostructures were fabricated from carbon nanotubes and graphite oxide aqueous suspensions. The analysis of carbon nanotubes coatings revealed that their morphology depends on synthesis parameters. The surface properties of these coatings depend on the amount and nature of functional groups attached to carbon nanotube walls. The analysis of graphite oxide films indicated that Congo red dye addition leads to more compact structure of the nanocomposites due the interaction between functional groups of these particles.

Single-walled carbon nanotubes are naturally-forming nanostructures that have attracted considerable recent research interest due to their unique opto-electronic properties and comparative ease of fabrication. Two-thirds of nanotube species are semiconductors due to symmetry conditions imposed by their pseudo-one-dimensional tubular structure, and exhibit band-gap photoluminescence when isolated from their environment. Despite their elegant structural simplicity, fundamental properties of carbon nanotubes, such as their intrinsic quantum efficiency, non-linear excitonic recombination mechanisms, and the role of environmental effects, continue to be disputed in the literature. The design of an apparatus capable of observing nanotube photoluminescence is presented, along with conclusive proof of the observation of a single (9,8)-chirality nanotube in the form of spectral, spatial, and polarization-dependent measurements. The dependance of the excitation and emission spectra of a single nanotube on the excitation intensity is explored and the emission spectra found to be described by a Gaussian peak function, in contrast to previously-reported results. The unexpected ability to cause redshifts in the emission spectrum via the ambient humidity is discovered, which has consequences on experimental best practices. Photoluminescence quantum efficiencies are measured to be 4±2% and 13±6% for two different nanotubes. This is at the high end of the range for comparable literature results, and supports the validity of a recent literature value for the effective atomic absorption coefficient for carbon, AC=1.6×10^−3nm^2, which is ten times greater than previous literature values. Pulsed power dependence studies show that the PL emission undergoes ‘hard’ saturation at an excitation intensity of 0.5×10^12photons/pulse/cm2, which is at least 100 times lower than previous reports and provides insight into non-linear decay dynamics. A novel theoretical model is developed to explain this saturation process, which yields an absorption co-efficient of AC=1.2±0.3×10^−3nm^2 as a fit parameter. Time-resolved photoluminescence dynamics are explored using femtosecond excitation correlation spectroscopy. Results suggest that the one-body decay processes are bi-exponential, with time constants of 31±4ps and 313±61ps, but also highlight the limitations of this technique in observing the expected very rapid (~1 ps) two-body Auger recombination process. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-09-26 16:23:40.81