Dentre as formas alotrópicas do carbono, o grafeno merece destaque. Este material consiste de uma monocamada atômica de carbono sp2 disposta em uma rede bidimensional cristalina hexagonal tipo favo de mel. Uma das formas de se obter o grafeno é pela esfoliação química, que consiste da oxigenação do grafite policristalino em um ambiente altamente oxigenado, formando um produto intermediário chamado de grafeno oxidado (GO). Por este método, gera-se um produto altamente estável e solúvel em água, podendo ser utilizado na construção de filmes ultrafinos. Uma das aplicações possíveis do grafeno oxidado é em sensores e biossensores, área de aplicações de novos materiais que viabilizem o diagnostico rápido, preciso, seletivo e de baixo custo, principalmente os do tipo, point-of-care. O grafeno é um forte candidato, nessa área, devido a sua alta performace e seu baixo custo de processamento. Neste trabalho, a técnica de automontagem eletrostatic layer-by-layer (ELBL) foi utilizada na construção de filmes de grafeno oxidado, juntamente com o policátion dendritico poli(amido amina) geração 4 (PAMAM-G4) em uma plataforma potenciométrica, utilizando um amplificador de instrumentação comercial AD620 como transdutor em um sensor de pH para caracterização da sensibilidade do dispositivo. Diversas técnicas espectroscópicas, óticas e morfológicas foram utilizadas para caracterizar a esfoliação química do grafite e dos filmes automontados. Através destas caracterizações mostrou-se que a esfoliação ocorreu satisfatoriamente concordando com resultados já existentes na literatura. A construção dos filmes ultrafinos ocorreu pela rápida adsorção do GO em camadas alternadas de PAMAM-G4, e o monitoramento do crescimento dos filmes foi realizado utilizando espectroscopia no UV-Vis, onde o crescimento é linear a partir da décima camada. Por microscopia de força atômica, mostrou-se que a adsorção das folhas de grafeno se dá primeiramente pelas folhas de menor número de camada (1 e 2 camadas) de GO e para camadas de número superior tem-se uma morfologia totalmente diferente da primeira. Por espectroscopia no infravermelho, mostrou-se a interação entre os dois polieletrólitos, onde há formação de ligações do tipo cross-linking entre as camadas. Medidas de potenciometria indicam a sensibilidade máxima em torno de 57 mV/pH em um substrato de ouro( sensibilidade Nerstiana), o que evidencia a sua aplicabilidade em sensoriamento e também a sua aplicação em biossensores. / Among the allotropic forms of carbon, graphene deserves special attention. This material consists of one atomic monolayer of sp2 carbon arranged in a two-dimensional hexagonal lattice type, namely \"honeycomb\". One common method to obtain graphene is -=by chemical exfoliation, which consists of oxygenation of polycrystalline graphite in a highly oxygenated medium, forming an intermediate product namely graphene oxide (GO). This method generates a highly stable and water soluble GO that can be used in the fabrication of ultrathin films. Graphene is a strong candidate for sensing, due to its high performance and low cost processing. In this dissertation, GO was obtained via chemical routs and processed in the form of ultrathin films in conjunction with polyamidoamine dendrimer (PAMAM G4) in a layered fashion using the Electrostatic Layer-by-Layer (ELBL). The GO/PAMAM films were deposited on potentiometric platforms and used as pH sensors using a commercial amplifier AD620 instrumentation as the detection technique. GO and the LbL films were characterized via spectroscopic, optical and morphological techniques. Film growth was monitored via UV-Vis spectroscopy and revealed a linear adsorption up to the tenth GO/PAMAM bilayer. AFM analyses revealed that graphene sheets containing 1 or 2 layers occurred adsorbed first on the substrates. Potentiometric measurements indicated a maximum sensitivity of ca. 57 mV/pH for GO/PAMAM films deposited on gold substrates (Nernstian Sensitivity), which demonstrates the applicability of the films in sensing and biosensing.

Polymer composites formed from layered fillers with high surface volume ratio show enhanced reinforcement. Graphite oxide is a high modulus material that can be separated into thin layers with high surface area. The aim of this study is to prepare polymer layered graphite oxide composites using functionalised polyolefin to enhance compatibility with various forms of layered graphite oxide in varying concentration. Functionalised polyolefins reinforced with layered graphite oxides and expanded graphite oxides were prepared using solution blending and melt blending methods. Three different mixing methods with varying shear intensity were employed to prepare polymer layered graphite oxide composites. The crystalline structure, thermal and mechanical properties of the prepared polymer layered graphite oxide composites was studied. Oxidised graphite prepared from the Staudenmaier method and its exfoliated form were dispersed in poly(ethylene-co-methyl acrylate-co-acrylic acid) (EMAA) via solution blending to prepare EMAA layered composites. The thermal stability was determined using thermogravimetric analysis. The EMAA layered composites showed higher thermal stability in comparison with pure EMAA. The mechanical properties of these EMAA layered composites were determined through dynamic mechanical analysis. Shear modulus, yield stress and storage modulus of EMAA in the presence of graphite oxide fillers decreased. A solution blending method was used to prepare poly(propylene-grafted-maleic anhydride) layered expanded graphite oxide composites (PPMA-EGO). Two types of PPMA-EGO were prepared using different mixing methods - low and high shear were employed. The effects of preparative mixing methods on the PPMA-EGO properties were investigated. The mechanical properties of PPMA-EGO obtained from dynamic mechanical analysis indicated that EGO had a reinforcing effect on the elastic behaviour of PPMA-EGO. This is due to strong interfacial adhesion between PPMA and EGO as a result of hydrogen bonding. The elastic behaviour of PPMA-EGO was affected by the surface area of graphite flakes. Low sheared PPMA-EGO elastic behaviour was found to be higher compared with that of high sheared PPMA-EGO. A melt blending method was used to prepare PPMA-EGO with varying EGO concentration. The interconnected network structure of EGO in the PPMA-EGO was not observed as shown by its scanning electron microscopy images. Thermogravimetric analysis of PPMA-EGO indicates increased decomposition temperature of the PPMA matrix. Dynamic mechanical analysis showed enhanced storage modulus of PPMA-EGO. The maximum elastic modulus of PPMA-EGO was observed at 3 %wt of EGO. The electrical conductivity of PPMA-EGO was measured only for EGO concentrations above 2 %wt. The EGO concentration was found to be the most critical factor in the enhancement of the electrical conductivity of PPMA-EGO. Wide angle X-ray diffraction analysis of all polymer layered graphite oxide composites revealed no change in interlayer spacing of graphite layers, indicating the absence of EMAA intercalation in the graphite layers. The crystallisation temperature and crystallinity of all polymer layered graphite oxide composites were determined using differential scanning calorimetry. The results indicated that graphite oxide and expanded graphite oxides acted as nucleating agents in inducing the crystallisation of functionalised polyolefin in the layered composites. However, the degree of crystallinity of functionalised polyolefin decreased in the layered composites.

Dans un souci de réduction du volume de déchets nucléaires et de revalorisation des matières combustibles, une stratégie de gestion du combustible des réacteurs à haute température (HTR) est développée dans cette étude. La réduction de volume passe par la séparation des particules TRISO hautement radioactives et du graphite faiblement radioactif (les deux étant réunis dans un assemblage de combustible appelé "compact") tandis que le recyclage total nécessite la séparation du coeur de la particule, valorisable, et de sa gangue, déchet ultime. Les méthodes de séparation doivent préserver l'intégrité des TRISO afin d'empêcher la fuite des radioéléments. Ainsi, le traitement de choc thermique entre l'azote liquide et l'eau chaude permet une division partielle des compacts mais ne permet de récupérer que peu de particules. L'érosion du graphite par jet d'eau à haute pression présente le risque de fracturer les particules. La combustion totale du carbone libère toutes les billes. Le traitement des compacts par les ultrasons dans l'eau érode le graphite en fonction de l'intensité de travail, des direction et distance d'attaque, de la température et du gaz de saturation, nettoyant les particules. L'attaque acide des compacts par un mélange H2O2 + H2SO4 provoque l'intercalation du graphite par l'acide, faisant gonfler la structure et libérant ainsi les billes intactes. Les TRISO d'une part et leurs gangues d'autre part ont ensuite été vitrifiées par frittage de manière à obtenir une forte densité, jusqu'à un taux de 25% vol. Enfin, la lixiviation des composites dans l'eau ultrapure à 90°C montre de fortes propriétés de confinement.

L'objectif de cette étude est l'élaboration de nanocomposite à base d'un élastomère de styrène et de butadiène (SBR) par l'ajout d'une dispersion aqueuse (slurry) de nanocharges lamellaires de phosphate de zirconium en phase α (α-ZrP ou ZrP). Les travaux s'attardent d'abord sur le mélange entre le SBR à l'état fondu et le slurry de ZrP en absence de traitement de surface. Différents stratégies d'élaboration sont ensuite envisagées afin d'améliorer la dispersion (intercalation exfoliation) des feuillets de ZrP dans le matériau en couplant le traitement de surface du ZrP et les paramètres de mise en œuvre. Différents traitements de surface sont abordés avec l'utilisation d'un agent intercalant métallique (Na+), de deux intercalants alkylamines (propylamine, octadécylamine) et d'un agent d'exfoliation (hydroxyde de tétrabutylammonium). En parallèle, plusieurs procédés de mise en œuvre générant des écoulements complexes sont utilisés. La complémentarité entre la diffraction des rayons X (DRX), la microscopie électronique en transmission (MET) et la spectroscopie mécanique (DTMA) permet d'obtenir une analyse multi-échelle de l'état de dispersion du ZrP et de proposer des scénarii décrivant les mécanismes de dispersion en fonction des paramètres étudiés. Un effort important est apporté pour la compréhension de la relation structure à l'échelle nanoscopique et les propriétés macroscopiques du matériau. Une étude comparative est ensuite proposée entre les valeurs expérimentales de l'effet de renforcement des matériaux et les prédictions des modèles Krieger-Dougherty et Halpi-Tsai

In this thesis study, the use of clay-polymer nanocomposites for their applicability in landfill sites as a product of retardation of waste water infiltration was evaluated. For this purpose, organophilic clays from HDTMA+ organic cation and nanocomposites of montmorillonite were prepared. The bentonite samples B1, B2 and B3 dominantly contain 2:1 layer montmorillonite and 1:1 interstratification of illite/smectite mixed layer as clay minerals. B1 is an unmodified yellow bentonite and B2 is a grey bentonite modified from B1, by the addition of Na2CO3 (Soda Ash). They were obtained from Han&ccedil / ili (Kalecik-Ankara) bentonite deposit which belongs to the Hancili Formation of Early Pliocene age. B3 is a standard Wyoming (SWy-1) white bentonite and belongs to the Newcastle formation of Cretaceous age. Their cation exchange and swelling capacity values were determined and the values increase from B1, B2 to B3. In order to produce clay-polymer nanocomposites, firstly organoclays were produced in bentonite samples. Claypolymer nanocomposite production was achieved by in situ intercalative polymerization successfully with intercalation and partly exfoliation of clay minerals with polyacrylamide (PAM). The samples of sand (S1), sand+bentonite (S2) and sand+nanocomposite (S3) mixtures were prepared and their permeability was determined. As a result of these values, the permeability of samples decrease from S1, S2 to S3. The results imply that the permeability of sample decreases as the claypolymer nanocomposite content increases resulting in a retardation of water penetration throughout the sample. The product has a potential to be used as a retardant for waste water infiltration in landfill sites.

Al-Zn-Mg-Cu (7xxx series) aluminium alloys are widely used for aircraft structures. It is difficult to obtain a combination of optimal strength and stress corrosion cracking (SCC) resistance for these alloys. It appears that SCC resistance of these alloys is related to grain boundary precipitate morphology. One technique to control the grain boundary precipitate morphology is to introduce a controlled cooling procedure referred to as High Temperature Pre-precipitation (HTPP) treatment following the solution heat treatment. There is need for a detailed study of the effect of HTPP on the properties of commercial Al-Zn-Mg-Cu alloys using different intermediate temperatures. In this thesis research, the results of ten HTPP processes applied to 7075 and 7050 commercial 7xxx series alloys are presented in terms of hardness, electrical conductivity, corrosion resistance, TEM analysis of grain boundary precipitate morphology and EDS analysis of solute concentration profile at the grain boundary. Results indicate that subsequent to HTPP processing, the 7050 alloy can be precipitation aged to a higher hardness compared to 7075; this result is associated with the modification of 7050 alloy by zirconium versus chromium in 7075 alloy. HTPP heat treatment achieves better SCC resistance compared to standard T6 temper. However, it does not appear that HTPP can achieve a combination of hardness, electrical conductivity and corrosion resistance superior to standard T6 and T7X tempers. / October 2014

Graphene is a two-dimensional sp2 hybridized carbon lattice that is also the fundamental building block of graphite. Graphene has attracted significant interest recently due to its distinctive electrical, optical and mechanical properties. These properties have spurred research directed at modifying graphene for use in a variety of electronic, optoelectronic, and sensor technologies. However, before graphene can be used in products, it is necessary to find methods to tune, modify, grow and integrate graphene features while substantially boosting device performance and maintaining current processing compatibility and ease of integration with existing manufacturing infrastructure. This dissertation focuses on developing techniques for controllably doping the graphene layer through scalable, industry friendly and simple chemical doping; using self-assembled monolayer compounds, photo-acid and photo-base generators, polymers and metal-organic species. We have, in fact, demonstrated simple p-n junctions fabricated in this manner. Characteristic I-V curves indicate the superposition of two separate Dirac points from the p and n regions, confirming an energy separation of neutrality points within the complementary regions; Raman studies of these methods have shown that these processes result in extremely low defect levels in the graphene. Our simple methods for producing patterned doping profiles in graphene films and devices open up a variety of new possibilities for forming complex doping profiles in a simple manner in graphene. This work can enable rapid testing, such as controlled work function tuning, complex doping profiles and simple post-fabrication tuning, of concepts for graphene that may be useful in both interconnect and transparent conductor applications. In addition to graphene doping, we also investigated approaches to the synthesis of few-layer graphene flakes, since current techniques still produce inferior materials. Exfoliation of Graphene Sheets by an Electron Donor Surfactant was demonstrated to generate few-layers graphene flakes that rival the electrical quality of reduce graphene-oxide (rGO) flakes. Last but not least, Diels-Alder adducts on silica were explored as a controllable carbon precursor for pristine graphene; these allow for a rational direct-growth-of-graphene-on-surface reaction mediated by copper catalyst, without the use of flammable precursors, such as methane, that are used in current methods of chemical vapor deposition synthesis of graphene.

In this research we have investigated electrochemical and impedance characteristics of liquid phase exfoliated graphene electrodes. The exfoliated graphene electrodes were characterized in Electrochemical Double Layer Capacitors (EDLCs) geometry. Liquid phase exfoliation was performed on bulk graphite powder in order to produces few layer graphene flakes in large quantities. The exfoliation processes produced few layer graphene based materials with increased specific surface area and were found to have suitable electrochemical charge storage capacities. Electrochemical evaluation and performance of exfoliated graphene electrodes were tested with Cyclic Voltammetry, constant current charging discharging and Electrochemical Impedance Spectroscopy (EIS) at ambient conditions. We have used several electrolytes in order to evaluate the effect of electrolyte in charge storage capacities. Specific capacitance value of ~ 47F/g and ~ 262F/g was measured for aqueous and ionic electrolytes respectively. These values are at least an order of magnitude higher than those obtained by using EDLC's electrodes fabricated with the bulk graphite powder. In addition these EDLC electrodes give consistently good performance over a wide range of scan rates and voltage windows. These encouraging results illustrate the exciting potential for high performance electrical energy storage devices based on liquid phase exfoliated graphene electrodes.

Master of Science / Department of Chemical Engineering / James H. Edgar / Hexagonal boron nitride has been used as an inert, refractory material with excellent resistance to thermal decomposition and oxidation for more than fifty years. In the past few years, hBN has been targeted for potential electrical and optical devices such as neutron detectors, ultraviolet light emitters, deep ultraviolet light detectors, and substrates for graphene and other atomically-thin two-dimensional materials. All of these potential applications benefit from high quality, single crystals, with thicknesses varying from nanometers to microns. This research was undertaken to investigate four aspects of hBN crystal growth and recovery. (1) In an effort to optimize hBN crystal growth from a nickel-chromium flux, a series of stepped cooling experiments were undertaken. The temperature profile was stepped in a way as to promote growth in both the a and c directions, at their optimal growth conditions. Crystals were found to be typically 100-500 µm across and thickness of approximately 20-30 µm with a pyramid-like crystal habit. (2) A method for the removal of hBN crystals prior to freezing of the metal flux was demonstrated using a specialized hot pressed boron nitride crucible capable of removing hBN crystals from the flux in situ. (3) Growth of isotopically pure hBN crystals was undertaken. By modifying the crucible material for solution growth, enrichment of hBN crystals over 90% was accomplished. (4) Exfoliation of hBN has many potential applications, specifically as graphene-hBN heterostructures where layers approaching thicknesses of single atoms are most effective surface to interact with graphene as an electronic device. Several methods were tested toward exfoliating a single crystal resulting in few-layered hexagonal boron nitride nanosheets. As a result of these investigations a greater understanding of hBN bulk growth, its isotopic enrichment, its recovery, and its exfoliation was obtained.

A reabsorção radicular é um evento fisiológico para os dentes decíduos. Porém, há casos em que esses dentes são mantidos à cavidade bucal além do tempo de esfoliação normal, mesmo quando os dentes permanentes sucessores estão presentes. Como são escassos os dados disponíveis sobre a real causa da retenção prolongada dos dentes decíduos, as razões exatas merecem ser investigadas. O objetivo desta pesquisa foi analisar se fatores locais (RANKL, RANK, OPG, MCP-1, RUNX2) ou sistêmicos (vitamina D, PTH, IGF-I) poderiam estar relacionados à biologia óssea e radicular em casos de retenção prolongada de dentes decíduos, com presença dos dentes permanentes correspondentes in situ, a fim de se buscar compreender possíveis etiologias do quadro. Para isso, foram selecionados pacientes com dentes decíduos em retenções prolongadas (n=14, grupo R) e pacientes sem dentes decíduos retidos (n=14, grupo C), mas com indicações ortodônticas de exodontias. Após as extrações dentais, foram coletados remanescentes do ligamento periodontal em torno das raízes dentais e amostras de sangue dos pacientes, que foram avaliados por qPCR e quimioluminescência, respectivamente. Houve diferença estatisticamente significante para RANKL (p=0,023) entre os grupos C e R, com menor expressão gênica de RANKL no grupo R. Da mesma forma, foi observada uma menor expressão de RANK no grupo R, comparado ao grupo C; contudo, essa diferença não foi significativamente diferente. Houve também um resultado próximo do valor de significância para vitamina D (p=0,0572), com níveis séricos reduzidos dessa vitamina no grupo R. Não houve diferenças estatisticamente significantes entre os grupos para os outros fatores estudados. Com base nos dados deste estudo, pode-se sugerir que menores expressões de RANKL e RANK possam estar envolvidas na retenção prolongada de dentes decíduos e que baixos níveis séricos de vitamina D também possam estar associados com o retardo na esfoliação radicular decídua. / Root resorption is a physiological event for primary teeth. However, there are cases where these teeth are maintained beyond the normal exfoliation time, even when the corresponding permanent teeth is present. Since there are few data concerning the real cause of prolonged retention of primary teeth, the exact reasons must be investigated. The aim of this study was to assess if local factors like RANKL, RANK, OPG, MCP-1, RUNX2, or systemic factors such as vitamin D, PTH and IGF-I could to be involve in the bone and root biology, in cases of persistent primary teeth, with the corresponding permanent teeth in situ. Patients with persistent primary teeth (n=14, group R) and patients without persistent primary teeth (n=14, group C), but with orthodontic indication of tooth extraction, were selected. After the teeth extractions, remaining periodontal ligament around the roots and blood samples were collected and assessed by qPCR and chemiluminescence, respectively. The present study found significant lower level of RANKL in the group R compared to group C (p=0,023). Although it was not significantly different, the level of RANK was also reduced in group R compared to group C. The expression of others local factors was similar between group R and C. Concernig systemic factors, the serum level of vitamin D were reduced in the group R compared to group C (p=0,0572) although it was not statistically significant. There were no significant differences between both groups for the others systemic studied factors. It is possible that a lower RANKL and RANK expression is involved in prolonged retention of primary teeth and our data also suggest that low serum levels of vitamin D could also be involved in the etiology of the retention.