Call number: LD2668 .T4 1986 B724 / Master of Science / Physics

Phase change materials (PCMs) have the ability to store thermal energy as latent heat over a nearly isothermal temperature range. Compared to sensible heat storage, properly chosen PCMs can store an order of magnitude more energy when undergoing phase change. Organic PCMs present several advantages including their non-corrosive behavior and ability to melt congruently, which result in safe and reliable performance. Because of these qualities, organic PCMs have been proposed for use in latent heat thermal storage systems to increase the energy efficiency or performance of various systems such as cooling and heating in buildings, hot water heating, electronics cooling, and thermal comfort in vehicles. Current performance is hindered by the low thermal conductivity, which significantly limits the rate of charging and discharging. Solutions to this challenge include the insertion of high conductivity nanoparticles and foams to increase thermal transport. However, performance validation remains tied to thermal conductivity and latent heat measurements, instead of more practical metrics of thermal charging performance, stability of the composite, and energy storage cost. This thesis focuses on the use of graphite nanoplatelets and graphite foams to increase the thermal charging performance of organic PCMs. Stability of graphite nanoplatelets in liquid PCM is realized for the first time through the use of dispersants and control of the viscosity, particle distribution, and oxidation. Thermal charging response of stable graphite nanoplatelet composites is compared to graphite foam composites. This study includes a correlation of thermal conductivity and latent heat to material concentration, geometry, and energy storage cost. Additionally, a hybrid PCM storage system of metal foam combined with graphite nanoplatelet PCM is proposed and evaluated under cyclic thermal conditions.

The focus of this study was to explore process-structure-property relationships in biodegradable polymer nanocomposite films in order to eliminate the commonly used trial and error approach to materials design and to enable manufacturing of composites with tailored properties for targeted applications. The nanofiller type and concentration, manufacturing method and compounding technique, as well as processing conditions were systematically altered in order to study the process-structure-property relationships. Polylactic acid (PLA) was used as the polymer and exfoliated graphite nanoplatelets (GNP), carbon nanotubes (CNT), and cellulose nanocrystals (CNC) were used as reinforcement. The nanocomposite films were fabricated using three different methods: 1) melt compounding and melt fiber spinning followed by compression molding, 2) solution mixing and solvent casting, and 3) solution mixing and electrospinning followed by compression molding. Furthermore, the physical properties of the polymer, namely the crystallization characteristics were altered by using two different cooling rates during compression molding. The electrical response of the composite films was examined using impedance spectroscopy and it was shown that by altering the physical properties of the insulating polymer matrix, increasing degree of crystallinity, the percolation threshold of the GNP/PLA films is significantly reduced. Additionally, design of experiments was used to examine the influence of nanofiller type (CNT versus GNP), nanofiller content, and processing conditions (cooling rate during compression molding) on the elastic modulus of the composite films and it was concluded that the cooling rate is the primary factor influencing the elastic modulus of both melt compounded CNT/PLA and GNP/PLA films. Furthermore, the effect of nanofiller geometry and compounding method was examined and it was shown that the high nanofiller aspect ratio in the CNT/PLA films led to decreased percolation threshold compared to the GNP/PLA films. The melt compounded GNP/PLA films displayed a lower percolation threshold than the solution cast GNP/PLA films most likely due to the more homogeneous distribution and dispersion of GNP in the solution cast films. Fully biodegradable and biorenewable nanocomposite films were fabricated and examined through the incorporation of CNC in PLA. Through the addition of CNC, the degree of crystallinity of the matrix was significantly increased. Focusing the design space through investigation of process-structure-property relationships in PLA nanocomposites, can help facilitate nanocomposites with tailored properties for targeted applications.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

This thesis presents a study of two-dimensional electron systems in GaAs-(Al,Ga)As heterojunctions and quasi-two-dimensional electron and hole systems in graphite within the quantum Hall effect regime of low temperature and high magnetic field. This thesis covers three main sets of experimental work as well as details of the experimental methods (chapter 2) used and the background theory behind the observed results (chapter 1). The first experimental results presented in this thesis in chapter 3 focus on contactless measurement of the equilibrium magnetisation of sample A2268, a ten layer multiple quantum well sample. Fitting the shape of dHvA oscillations at various temperatures to different models for the density of states, various properties of the system can be estimated, such as the shape of the disorder-broadened density of states and the presence of a background density of states between the Landau levels. Chapter 4 focuses on measurements of the decay of induced circulating currents in the quasi-dissipationless quantum Hall regime in two samples, V0049 and T73. The induced current is measured via contactless measurement of the associated magnetic moment. The magnitude of the induced current is found to be affected by the sweep rate of the magnetic field and also the distance of approach. The decay of the induced currents is observed at several temperatures and for different magnetic field sweep rates and distances of approach. Decays are observed for up to several days at time, far longer than previously possible. Information about the rate of decay can be used to build a picture of the decay mechanisms present in the quantum Hall regime. The presence of a power-law decay regime indicates many decay mechanisms contribute to the decay of a circulating current in the quasi-dissipationless quantum Hall regime. Chapter 5 focuses on both contactless magnetometry and transport experiments carried out on a graphite sample. The experiments aim to confirm or dispute recent claims of Dirac fermions in graphite. Experiments are carried out at temperatures in the range 30 mK to ~4 K and at two different angles to the applied magnetic field. Phase analysis of both Shubnikov de Haas and de Haas van Alphen oscillations is used to distinguish between normal and Dirac fermions. Observation of quantum Hall effect displays the presence of a half-integer quantum Hall staircase similar to that observed in graphene.

The rapid development of polymer nanocomposites has received extensive attention over the last few decades. The ability to alter functionalities of composites, dramatically improving properties and performance at low filler content creates flexibility in designing materials for advanced applications in various industrial fields. This work focuses on nanocomposites relevant to the packaging and aerospace industries. This work evaluated the ability to homogeneously distribute nanomaterials into a polymer matrix, understand the effects on rheological properties, understand changes to microstructure and effects, and characterize properties of resulting nanocomposite. High torque melt mixing was used to disperse surface modified cellulose nanocrystals in a poly(lactic acid) (PLA) resin and graphene in a phenylethynyl terminated imide resin, PETI 298, using bulk graphite. Rheology, Raman spectroscopy, and X-Ray powder diffraction were applied for the understanding of changes to the microstructure and location of optimum loading by the determination of the percolation threshold. Thermomechanical performance was evaluated through TGA, DMA, and DSC. It was determined that graphene and short stacks of graphene could be dispersed and distributed at low loadings in PETI 298. As expected, the addition of graphitic material led to an increase in viscosity, but also caused a retardation of the cure which could be attributed to increased viscosity or quenching of free radicals. Changes to the microstructure were difficult to evaluate because of the competing chemistry occurring in the system but it could be determined that something significant occurs around 1 wt % at which the melt rheology and the microstructure behavior was different from other composites. It was further determined that the melt mixing process led to the formation of an ordered structured. Modification of the cellulose nanocrystals (m-CNC) with Cardura, glycidyl ester, provided no improvement to mechanical properties of PLA composites. However, m-CNCs were found to nucleate the crystallization of PLA. Lack of improvement to mechanical properties could be attributed to the degradation of polymer during processing.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The aim of this thesis is to elaborate a strategic analysis of the company KOH-I-NOOR Grafit, s.r.o., on this basis set vision and conceive a strategy suggestion. Principal methods of external analysis are PEST analysis and Porter's 5-forces model, in internal analysis are used analysis of internal sources and financial analysis. The next method is SWOT analysis, which sums up and interconnects the most important findings of previous analyses; on this ground is set a strategy of a chosen company and suggest a strategy.

Eletrodos compósitos à base de grafite/poliuretana foram preparados contendo diferentes quantidades de hexacianoferratos de cobre(II), cobalto(II) e ferro(III). Os complexos foram preparados de acordo como procedimentos descritos na literatura e caracterizados por análise elementar, análise térmica e espectrometria na região do infra-vermelho. A análise térmica mostrou que há 10 moléculas de água de hidratação no hexacianoferrato de cobre(II), 11 no hexacianoferrato de cobalto(II) e 16 no hexacianoferrato de ferro(III). Após desidratação ocorre decomposição exotérmica violenta dos complexos. No caso do cobre a decomposição se dá com formação de CuO seguida da degradação do Fe(CN)3 com formação de Fe2O3. Para o hexacianoferrato de cobalto(II) e o hexacianoferrato de ferro(III) a mistura de Co3O4/Fe2O3 e o Fe2O3, respectivamente, se formaram após uma única etapa de decomposição. Apenas os eletrodos preparados com os complexos de cobalto e cobre apresentaram sinais voltamétricos, enquanto que o complexo de ferro não respondeu, provavelmente devido à sua baixa solubilidade em água. As condições de preparação dos eletrodos, tais como composição, ordem de adição de reagentes, pH, eletrólito suporte e intervalo de potenciais foram otimizadas. Um mecanismo para explicar a não estabilização do sinal voltamétrico, mesmo após ciclagem de potencial foi proposto com base na baixa solubilidade dos sais em água e a sua imobilização no eletrodo sólido a qual dificulta a formação do filme de hexacianoferrato na superfície. Finalmente um método analítico para a determinação de piridoxina, usando o eletrodo de grafite/poliuretana modificado com hexacianoferrato de cobre(II) foi proposto, com base na redução de sinal do complexo, na presença do analito. Neste caso foi observada uma resposta linear entre 1,08 x 10-6 a 1,07 x 10-5 mol L-1, com limite de detecção de 8,78 x 10-7 mol L-1 (3 x S/N) e o método foi aplicado na determinação de piridoxina em duas formulações comerciais. Coeficientes de recuperação entre 98-120% foram observados sem interferência dos componentes das formulações e sem necessidade de renovação da superfície do eletrodo. / Graphite-poliurethane solid composite electrodes were prepared containing different amounts of copper(II), cobalt(II) and iron(III) hexacianoferrates. The complexes were synthesized according to procedures previously described and characterized using elemental analysis, infrared spectrometry and the thermal analytical techniques: thermogravimetry/derivative thermogravimetry and differential thermal analysis. The thermal analysis revealed that there are 10 hydration water molecules in the copper(II) hexacianoferrate, 11 in the cobalt(II) and 16 in the iron(III) complexes. After dehydration, a strong exothermal degradation occurred in all cases. The copper complex decomposed in two steps with generation of CuO, followed by degradation of the Fe(CN)3 and formation of Fe2O3. The cobalt(II) and iron(III) hexacianoferrates decomposed in a single step with generation of Co3O4/Fe2O3 mixture and Fe2O3 as residues respectively. Only the electrodes prepared with copper and cobalt complexes presented voltammetric signals, while the iron complexes did not responded, probably due to its very low solubility in water. The conditions for the electrode preparation such as composition, order of addition of the components supporting electrolyte, pH and useful potential window were optimized. A mechanism to explain the non-stabilization of the voltammetric signal even after 200 cycles has been proposed on the basis of the complexes solubility in water as well as the immobilization of the complex in the solid electrode that turns difficult the formation of the hexacianoferrate film on the electrode surface. Finally, a graphite polyurethane electrode modified with the Cu(II) hexacianoferrate has been used in the voltammetric determination of pyridoxine, based on the diminution of the voltammetric signal of the modifier in the presence of the analyte. In this case a linear dynamic range of 1.08 x 10-6 to 1.07 x 10-5 mol L-1, with a detection limit of 8.78 x 10-7 mol L-1 (3 x S/N). The proposed electrode was used in the determination of pyridoxine in two solid pharmaceutical formulations with recoveries of 98 - 120% without interference of the other substances present in the formulation and no adsorption on the electrode surface.