Thesis (Ph.D.). / Written for the Dept. of Mechanical Engineering. Title from title page of PDF (viewed 2009/06/10). Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1991.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 107-112).

<p> This thesis deals with the analytical and experimental study of buckling strength, of thin walled channel struts, of different geometrical dimensions. The influence of the dimensions of the columns on the buckling strength has been studied.</p> <p> The experimental work consisted of testing different channels of thin sheeting to failure. Comparison has been made with the previous work done and a comparison is made between the theoretical predicted values and the experimental results. The Appendix includes detailed mathematical procedure and matrices formulations.</p> / Thesis / Master of Engineering (MEngr)

Safe, lightweight, and cost-effective materials are required to practically store hydrogen for use in portable fuel cell applications. Compressed hydrogen and on-board hydrocarbon reforming present certain advantages, but their limitations must ultimately render them insufficient. Storage in hydrides and adsorption systems show promise in modeling and experimentation, but a practical medium remains unavailable. Since the earliest report of adsorption on single-walled carbon nanotubes (SWNT) in 1997, a number of controversial publications have claimed the hydrogen capacity of these materials to be between 0.1 to 10 wt. %. However, no study has yet demonstrated a plateau of adsorption with pressure that would verify the reported capacity. A volumetric adsorption measurement instrument was designed and constructed to resolve this controversy. The instrument is capable of degassing samples under high vacuum and offers unprecedented measurements of hydrogen storage up to a pressure of 300 atm and a broad range of temperatures. In addition, an electrical probe within the sample cell was designed to study the mechanism of adsorption in situ. The best hydrogen storage observed on bundles of purified SWNT was 1.6 wt. % at 264 atm and 200 K. At room temperature, a high-pressure plateau was found corresponding to an adsorption of 0.9 wt. % at a pressure of 300 atm, which equates to an adsorption to surface area ratio of 1.14 wt. %/l 000 m2/g. Contrary to the claim by the Caltech Group [Ye et al., 1999], resistance measurements of purified SWNT bundles revealed that bundles do not separate under high pressure. Instead, the bundles were found to compress under the action of external pressure, leading to an increase in conductivity with pressure. A simple geometrical model suggests that without this bundle separation the volume displaced by the sample may counteract the benefit gained by adsorption because of the increase in gas density at high pressure. The isosteric heat of adsorption on SWNT bundles was measured to be between 3.9 and 5.0 kJ/mol at low levels of adsorption, and the activation energy for adsorption determined by the Langmuir model was found to be 1.9 kJ/mol. These low energy parameters are indicative of weak physisorption. / Thesis / Master of Applied Science (MASc)

Macro lambda is a parameter for predicting the weight savings for using different material. Macro lambda approximates the response of a thin-walled structure to a change in material thickness. The relationship between macro lambda and weight savings for material substitution is given. The results of nine major joints for a car cab model are given. Two kinds of structural element for weight advantage of aluminum, magnesium and other light materials are given: curved beam in-plane bending, curved beam out-of-plane bending. Bulkhead reinforcement is given for a T-Joint model. The application shows a dramatic reduction of macro lambda for T-Joint x moment and y moment load, which means the weight advantage of light materials is reduced after the reinforcement applied. For the z moment load T-Joint model, adding center layer reinforcement gives the largest reduction of macro lambda and maximum von Mises stress. The bulkhead reinforcement is then used for two car cab joints: B-pillar to rocker joint and hinge pillar to rocker joint. The results indicate that the bulkhead reinforcement near the center area gives the biggest reduction for macro lambda. Micro lambda, which is a value for element level, is introduced. The relationship between micro lambda and force distribution is given. Then it is used for the analysis of the force distribution along curved beam model when the thickness of the model is doubled. The results indicate that the force is redistributed from the corner to center of the flange for the curved beam model. So for curved beam model, light material such as aluminum, magnesium, which is thicker, is more efficiently used than steel. Micro lambda is used for the analysis of B-pillar to rocker joint of a car cab. The result indicates that the maximum micro lambda area is just the area where we apply the optimum bulkhead reinforcement. Micro lambda is also used for the analysis of AISI PNGV bending model. The result shows that the C-pillar area is the major problem area. Several reinforcements for the C-pillar area are given. The result shows that layer 31172 is most important for increasing the stiffness.

The discovery of nanotubes with unique mechanical, electrical, and thermal properties has led to their use in the development of the next generation of composite materials. However, their poor solubility and dispersion properties in any organic and aqueous solvents limits their potential applications. In order to improve their solubility, single-walled carbon nanotubes (SWNTs) were functionalized along their sidewalls with phenol groups using a 1,3-di^polar cycloaddition reaction. These phenols could be further derivatized with 2-bromoisobutyryl bromide, resulting in the attachment of atom transfer radical polymerization initiators to the sidewalls of the nanotubes. These initiators were found to be active in the polymerization of methyl methacrylate and t-butyl acrylate from the surface of the nanotubes. However, the polymerizations were not controlled, leading to the production of high molecular weight polymeric grafts with relatively large polydispersities. The resulting polymer carrying nanotubes were analyzed by IR, Raman spectroscopy, solid-state NMR, DSC, TEM, and AFM. The nanotubes functionalized with poly(methyl methacrylate) were found to be insoluble in organic solvents, such as THF and CH2CI2. However, the dispersion property of SWNTs in the polymer matrix was improved dramatically. Another monomer t-butyl acrylate (t-BuA) was also polymerized using the same macroinitiators. It was found that the SWNTs functionalized with t-BuA iii were soluble in a variety of organic solvents. The t-butyl groups of these appended polymers could also be removed to produce nanotubes functionalized with poly (acrylic acid), resulting in nanocomposites that are soluble in aqueous solutions. In addition, polystyrene (PS) which was prepared by stable free radical polymerization, was used to functionalize SWNTs through the radical coupling reaction. IR, NMR, TEM, and AFM confirmed that this polystyrene was covalently bonded to the SWNTs. It was also found that the resulting PS-SWNTs composites were quite soluble in organic solvents, such as THF and CH2C12. / Thesis / Master of Science (MSc)

Since their discovery in 1991, carbon nanotubes, and especially single walled carbon nanotubes (SWNTs), have attracted significant attention due to their unique structural, mechanical, and electronic characteristics. Although many potential applications for carbon nanotubes have been suggested, several key obstacles currently preclude their practical commercial applications. One of these is their lack of solubility and processability. In order to address this issue, a number of covalent and non-covalent nanotube functionalization techniques have recently been reported in the literature. These methods allow for the manipulation of nanotube properties, such as their solubility, through the attachment of various chemical moieties. Although most of these methods involve covalent attachment of structures to either the ends or sidewalls of SWNTs, several examples of non- covalent functionalization have also been reported. Pyrene, with its flat and aromatic structure, has been shown to form strong pi-pi stacking interactions with the surface of SWNTs. With this in mind, we explored several methods towards SWNT solubilization with diblock copolymers through non-covalent polymer- nanotube interactions. Living free radical polymerizations (SFRP, ATRP) were employed to produce diblock copolymers with narrow polydispersity. Commercial and synthetic monomers with different functionalities could be utilized to produce polymers with varying properties. Specifically, we used polymers such as polystyrene, poly(methyl methacrylate), poly(t-butyl acrylate) and poly(acrylic acid) as one block of our diblock copolymers. The second block was composed of synthetic pyrene-functionalized monomers mixed with different amounts of monomers that match the composition of the first block. It was found that, upon mixing these diblock copolymers with insoluble nanotubes in various solvents, the nanotubes were partially solubilized through pi-pi stacking with the pyrene- containing blocks. / Thesis / Master of Science (MS)

Single-walled carbon nanotubes (SWNTs) are a new class of materials that have recently attracted a great deal of interest because of their unique structural, mechanical, and electronic properties. Also, SWNTs have a high potential for a number of technological applications, including molecular electronics, emissive devices, and photovoltaic devices. To fully utilize their unique properties, control of the solubility, processibility, and functionality of SWNTs is required. Therefore chemical functionalization of SWNTs using a variety of methods, in either covalent or noncovalent manner, has been developed to produce soluble nanotube composites coupled with various chemical moieties. To explore the possibility of making potential soluble nanotube-based materials for solar cells, SWNTs were functionalized with organic chromophore-labeled polymers via a radical coupling process. The organic chromophore was used to absorb light to produce photo-induced electrons, while the polymer chains were used for improving the solubility of SWNTs. These novel chromophore-labeled polymers were made by stable free radical polymerization (SFRP), either using a synthetic chromophore-functionalized styrenic monomer or by derivatizing well-defined polystyrenes. Specifically, the chromophores employed in this investigation were commercially available 7-hydroxycoumarin and coumarin-343. In order to carry out fluorescence studies of SWNT-coumarin composites systematically, various factors were probed by (1) altering polystyrene lengths between the SWNT and the coumarin; (2) changing the distribution of coumarins along the polymer chain, in the form of either a block or random copolymer; (3) placing single coumarins on the surface of SWNTs. All of these resulting polymer functionalized SWNTs were found to be soluble in certain organic solvents such as CHCl3. Different absorption behaviors have been observed for SWNTs functionalized with 7-hydroxycoumarin containing copolymers. Fluorescence was still observable for all of these composites, and the pi-pi interactions between coumarins and nanotubes were believed to be responsible for the broadening of emission bands of the resulting composites. / Thesis / Master of Science (MS)

Single-w ailed carbon nanotubes (SWNTs) were oxidatively shortened and functionalized with ruthenium-based olefin metathesis catalysts. These catalyst-functionalized nanotubes were shown to be effective in the ring-opening metathesis polymerization of norbornene, resulting in rapid polymerization from the catalyst sites on the nanotube. It was found that high polymer molecular weights could be reached, and the molecular weight increased linearly with polymerization time. The resulting polynorbomene-functionalized nanotubes were found to exhibit solubility in organic solvents, while the starting materials and catalyst-functionalized nanotubes were completely insoluble. The polymerized materials were characterized by NMR, IR, DSC, AFM and TEM. Polystyrene and poly[(t-butyl acrylate)-b-styrene] with well-defined molecular weights and polydispersities were prepared by nitroxide-mediated free-radical polymerization. The homo- and block-copolymers were used to functionalize shortened single-walled carbon nanotubes (SWNTs) through a radical coupling reaction involving polymer-centered radicals generated at 125°C via loss of the stable free-radical nitroxide capping agent. The resulting polymer-SWNT composites were fully characterized and were found to be highly soluble in a variety of organic solvents. This solubility could also be altered through chemical modification of the appended polymers. The t-butyl groups of appended PtBA-b-PS could be removed to produce poly[(acrylic acid)-b-styrene]- functionalized carbon nanotubes. The resulting composite was found to form aggregates in a mixture of chloroform/methanol (v/v: 1/1), as determined by dynamic light scattering (DLS). / Thesis / Master of Science (MS)