Transport Properties of Nanocomposites were studied in this work. A Monte Carlo technique was used to model the percolation behavior of fibers in a nanocomposite. Once the percolation threshold was found, the effect of fiber dimensions on the percolation threshold in the presence and absence of polymer particles was found. The number of fibers at the percolation threshold in the presence of identically shaped polymer particles was found to be considerably lower than the case without particles. Next, the polymer particles were made to be of different shapes. The shapes and sizes of the fibers, as well as the polymers, were made the same as those used to obtain experimental data in literature. The simulation results were compared to experimental results, and vital information regarding the electrical properties of the fibers and fiberfiber junctions was obtained for the case of two stabilizers used during composite preparation ? Gum Arabic (GA) and Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). In particular, the fiber-fiber connection resistances, in the case of these 2 stabilizers, were obtained. A ratio between the fiber path resistance and the total connection resistance, giving the relative magnitude of these resistances in a composite, was defined. This ratio was found through simulations for different fiber dimensions, fiber types and stabilizers. Trends of the ratio with respect to composite parameters were observed and analyzed, and parameters to be varied to get desired composite properties were discussed. This study can serve as a useful guide to choose design parameters for composite preparation in the future. It can also be used to predict the properties of composites having known fiber dimensions, fiber quality and stabilizing agents.

Health monitoring is an important field as small failures can build up and cause a catastrophic failure. Monitoring the health of a structure can be done by measuring the motion of the structure through the use of strain sensors. The limitations of current strain sensing technology; cost, size, form could be improved. This research intends to improve current strain sensing technology by creating a conductive polymer composite that can be used monitor health in structures. Conductive polymer composites are a viable candidate due to the low costs of manufacturing, tailorable mechanical and electrical properties, and uniform microstructure. This work will focus on determining if a all-polymer composite can be used as a strain sensor, and investigating the effects of filler, doping and latex effect the electrical and strain sensing properties. Strain sensors were prepared from polyaniline (PANI)-latex composites, the morphology, mechanical, electrical and strain sensing properties were evaluated. These strain sensors were capable of repeatable measuring strain to 1% and able to measure strain until the substrates failure at 5% strain, with a sensitivity (measured by gauge factor) of between 6-8 (metal foil strain sensors have a gauge factor of 2). The best performing strain sensor consisted of 4 wt.% polyaniline. This composition had the best combination of gauge factor, linearity, and signal stability. Further experiments were conducting to see if improvements could be made by changing the polymer used for the matrix material, the molecular weight and the level of doping of the polyaniline. Results indicate through differences in strain sensing response; lower hysteresis and unrecoverable conductivity, that polyaniline latex composites can be adjusted to further improve their performance. The polyaniline-latex composites were able to repeatable measure strain to 1%, as well as strain until failure and with gauge factor between 6-8, and a 70% increase in signal at failure. These properties make these composites viable candidates to monitor health in structures, buildings, bridges, and damns.

Reproduction de : Thèse doctorat : Physique : Metz : 2003. / Titre provenant de l'écran-titre. Notes bibliographiques.

Thèse doctorat : Sciences de l'Environnement Industriel et Urbain : Villeurbanne, INSA : 2007. / Titre provenant de l'écran-titre. Bibliogr. p. 259-271. Glossaire.

Thesis (M. Phil.)--University of Hong Kong, 1981.

Thesis (M. Phil.)--University of Hong Kong, 1984.

published_or_final_version / Applied Geosciences / Master / Master of Science

No description available.

No description available.

This thesis presents a framework for a microstructural model of a catalyst layer in a proton exchange membrane (PEM) fuel cell. In this study, a stochastic model that uses individual carbon, platinum and ionomer particles as building blocks to construct a catalyst layer geometry, resulting in optimal porosity and material mass ratios has been employed. The construction rule set in this design is easily variable, enabling a wide range of catalyst layer geometries to be made. The generated catalyst layers were found to exhibit many of the features found in currently poduced catalyst layers. The resulting geometries were subsequently examined on the basis of electronic percolation, mean chord length and effective diffusivity of the pore phase. Catalyst layer percolation was found to be most effected by the number of carbon see particles used and the specified porosity. The mean chord lengths of all of the catalyst layer geometries produced Knudsen numbers ranging in order of magnitude between 0.1 and 10, thus indicating that gas diffusion within the catalyst layers lies in the transition regime between bulk and Knudsen diffusion. Calculated effective diffusivities within the pore space of the model were shown to be relatively insensitive to changes in the catalyst layer composition and construction rule set other then porosity, indicating that the pore size distribution does not significantly vary when the catalyst layer mass ratios vary. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-08-31 08:52:55.747