This dissertation describes the development of a processing route for fabricating conventional and doped multi-wall carbon nanotube (MWCNT)/polymer composite films for dielectric applications. Previous research has shown that such composites are promising dielectric materials, but their commercial development has been impeded by the nanotube agglomeration in the polymer matrix and the inefficiency in forming uniform films. Moreover, the harsh fabrication treatments often disrupt the structure of the nanotubes, hence damaging their inherent electrical properties. This work presents safer routes for forming non-aqueous, surfactant free dispersions of conventional and doped MWCNTs, which can be readily mixed with polymers and formed into films through aerosol spraying. Dispersibility behaviour of in-house synthesised conventional, nitrogen doped (N-MWCNTs), and boron doped (B-MWCNTs) MWCNTs was studied in 22 organic solvents. Based on thermodynamic theories it was suggested that doping, in particular nitrogen doping, significantly reduced the surface energy of the nanotubes. This aspect was crucial to understand the dispersibility of N-MWCNTs in low surface energy solvents and to achieve dispersions with high nanotube concentrations (0.82 mg/ml). Also, a "destruction reduced sonication protocol" involving mild sonication was suggested for forming MWCNT dispersions in organic solvents. Dispersions formed using this protocol were homogeneous and showed high stability of at least 2.5 years. Furthermore, the effect of ultrasonic probes on MWCNT lengths was studied and a decrease of 96–99% for MWCNTs and 85–95% for N-MWCNTs was observed. A numerical value for the nanotube length decrease during sonication has been reported for the first time. Preliminary studies to generate dielectric films of MWCNT/perfluoro alkoxy polymer were performed using aerosol spraying. An improvement in the dielectric constant (3.56) with a low dissipation factor (0.003) was observed in 0.3 wt.% B- MWCNT/PFA composite films. Consistency in the test results from various parts of the films confirmed the uniformity of the nanotube distribution within the composite. Future work should concentrate on the effects of B-MWCNTs and N-MWCNTs at the percolation threshold due to their inherent electric properties.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The present work describes the synthesis of a new catalyst of palladium nanoparticles supported on multi-walled carbon nanotubes containing nitrogen (Pd@CNxNCPM) 1 and its use in carbon-carbon coupling reactions (Suzuki and Heck) as well as reactions catalytic hydrogenation (reduction of double C-C bonds and nitro compounds reduction). The synthetic strategy employed afforded the simple way to obtain the catalyst with reaction in a short time and efficiently. To this was employed as the palladium precursor, the salt potassium hexacloropalladate IV and hydrazine monohydrate as the reducing agent, without the need for stabilizing agents for the control of nucleation and size of nanoparticle. The catalyst system was characterized as its morphology: dispersion, size and shape of nanoparticles by scanning electron microscopy. Also the catalyst was performed Raman spectroscopy and determination of amount of palladium. After characterization the catalyst, it was tested for coupling reactions of carbon-carbon: Suzuki and Heck leading to the formation of their products with 70-> 95% for Suzuki coupling and 75-> 95% for Heck. For the synthesis in question were used 0.5 mol% of catalyst (based amount of palladium) for Suzuki and 10 mol% for Heck. It should be noted that the catalyst shown stable in the reaction conditions tested, and observed the possibility of reuse of this system for additional reaction cycles without loss of efficiency for the Suzuki coupling. Also, the catalyst was efficient and chemoselectiv for catalytic hydrogenations of unsaturated carbon-carbon bonds and nitro compounds leading to their products in good yields. Thus, the synthesized catalyst proved versatile and can be used in reactions of carbon-carbon coupling well as in catalytic reduction may also be recovered and reused, which provides an environmentally friendly at the same characteristic. / O presente trabalho apresenta a síntese de um novo catalisador de nanopartículas de paládio suportadas em nanotubos de carbono de paredes múltiplas contendo nitrogênio (Pd@CNxNCPM) 1 e sua utilização em reações de acoplamento carbono-carbono (Suzuki e Heck) bem como em reações de Hidrogenações catalíticas (reduções de duplas ligações C-C e redução de nitrocompostos). A estratégia sintética utilizada permitiu a obtenção do catalisador de maneira simples, em curto tempo reacional e de maneira eficiente e sem a presença de agentes estabilizantes externos. Para isso foi empregado como precursor de paládio o sal hexacloropaladato IV de potássio e como agente redutor, hidrazina monohidratada sem a necessidade de agentes estabilizantes para o controle da nucleação e tamanho de nanopartículas. O sistema catalítico foi caracterizado quanto sua morfologia: dispersão, tamanho e forma de nanopartículas através de microscopia eletrônica de varredura. Também foi realizada espectroscopia Raman do catalisador bem como determinação do teor de paládio. Após devidamente analisado o catalisador, o mesmo foi testado para reações de acoplamento carbono-carbono de Suzuki e Heck levando a formação dos respectivos produtos com rendimentos de 70-> 95% para os acoplamentos de Suzuki e 75-> 95% para Heck. Para as sínteses em questão foram usados 0,5 mol% de catalisador (baseados na massa de paládio) para Suzuki e 10 mol% para Heck. Cabe salientar que o catalisador se mostra estável nas condições reacionais testadas, sendo observada a possibilidade de reuso deste sistema por ciclos reacionais adicionais, sem perdas de eficiência para o acoplamento de Suzuki. Ainda, o catalisador se mostrou eficiente para hidrogenações catalíticas quimiosseletivas de ligações de carbono-carbono insaturadas e nitrocompostos levando aos respectivos produtos em bons rendimentos. Dessa forma o catalisador sintetizado se mostrou versátil, sendo possível ser utilizado em reações de acoplamento carbono-carbono bem como em reduções catalíticas, também pode ser recuperado e reutilizado, o que confere ao mesmo uma característica ambientalmente correta.