Este trabalho traz a aplicação de alta pressão e alta pressão/temperatura (4.0 GPa e 400º C), em amostras de nanotubos de carbono de paredes múltiplas (NTCPM) comerciais para a obtenção de amostras compactas. Os NTCPM foram funcionalizados com ácido nítrico e ácido nítrico/ácido sulfúrico e, também foram usados nanotubos de carbono dopados com nitrogênio. Foram também processadas amostras contendo nanotubos de carbono de paredes múltiplas incorporados em matriz de zircônia obtida pelo método sol-gel. Para aplicação da alta pressão foi usado um sistema com câmaras do tipo toroidal, utilizando grafite como meio transmissor de pressão. Foram obtidas amostras macroscópicas autossuportadas e com resistência ao manuseio principalmente nas amostras de nanotubos de carbono funcionalizados com ácido nítrico/ácido sulfúrico incorporados em zircônia. Para a caracterização das amostras foram utilizadas as técnicas de Microscopia Eletrônica de Transmissão, Espectroscopia Raman, Difração de Raios X e isotermas de adsorção/dessorção de nitrogênio com as quais foi possível determinar que mesmo após a aplicação de alta pressão/temperatura os nanotubos de carbono não sofrem significativas modificações na sua estrutura e nas suas propriedades morfológicas e texturais, confirmando então que os NTCPM mantém suas características originais, apresentando condições para aplicações em dispositivos. As amostras macroscópicas contendo nanotubos de carbono de paredes múltiplas incorporados em zircônia apresentaram ainda resistência à carga de milhares de vezes o seu peso e comportamento de materiais semi-condutores. / This work presents the application of high pressure and/or high pressure/temperature (4.0 GPa and 400 ° C), on different samples of commercial multi-walled carbon nanotube (MWCNT) to obtain compacted samples. MWCNT were functionalized with nitric acid and nitric acid/sulfuric acid, and also carbon nanotubes doped with nitrogen. MWCNT incorporated in a zirconia matrix obtained by sol-gel method were also processed. For high pressure application it was used a system with the toroidal-type chamber, using graphite as a pressure transmitting medium. Self-supported macroscopic samples were obtained, easy to handle, especially in samples of functionalized carbon nanotubes with nitric and sulfuric acid and also incorporated in zirconia. To characterize the samples it was used Transmission Electron Microscopy, Raman Spectroscopy, X-ray diffraction and nitrogen adsoption/desorption isotherms and it was determined that even after application of high pressure/temperature carbon nanotubes do not suffer significant changes in their structure and in their morphological and textural properties, confirming that the CNT keeps its original characteristics and providing conditions for device applications. The macroscopic samples containing MWCNT incorporated in zirconia also exhibited resistance to load of thousands times its own weight and behavior like semiconductor materials.

Grâce à leurs propriétés mécaniques et électroniques élevées, les NanoTubes de Carbone (NTC) semblent être les nanocharges idéales pour conférer des propriétés optimum à des matériaux composites, en particulier ceux qui sont élaborés à partir de matrices élastomères. Cependant, pour obtenir une amélioration significative des propriétés une bonne dispersion dans la matrice est nécessaire. La dispersion des NTC dans une matrice élastomère de type EPM est explorée ici en employant un copolymère statistique, le poly(éthylène-stat-acétate de vinyle) (EVA), comme agent dispersant. Les outils classiques de mélange des élastomères, mélangeur interne et mélangeur à cylindres, qui sont des techniques de mélange douces, ont été utilisés dans le cadre de cette étude. Nous avons montré qu’à faible taux de NTC dans la matrice leur dispersion était contrôlée par deux paramètres clés (i) la viscosité de la matrice EPM et (ii) la concentration en EVA. L’augmentation des concentrations de NTC a permis de mettre en évidence que les propriétés rhéologiques et électriques des nanocomposites variaient brusquement à partir de concentrations critiques (seuil de percolation) assez faibles permettant de justifier l’utilisation du système EPM-EVA sélectionné. Nous avons alors préparé un mélange maître EPM-EVA chargé à 20% en NTC possédant de très bonnes propriétés de conductivité. Des mélanges à base d’EPDM chargés par des nanotubes de carbone, du noir de carbone ou le mélange des deux ont également été analysés. Nous avons démontré que la dilution d’un mélange maître permet d’obtenir un élastomère chargé en NTC avec une viscosité Mooney constante et avec un impact fort sur la cinétique de vulcanisation de l’élastomère (accélération de la réaction). Un effet de synergie entre noir de carbone et NTC a été mis en évidence au niveau des propriétés mécaniques mais pas pour les propriétés électriques. / The outstanding properties of Carbon NanoTubes (CNTs) make them ideal candidates for use in nanocomposites, and particularly in those based on rubber matrix. However, to obtain an improvement of the properties, a good degree of dispersion of the CNT in the matrix is crucial. The CNT dispersion in an EPM rubber is investigated here by using a statistical copolymer, the ethylene-stat-vinyl acetate (EVA), as dispersing agent. In this study, we work with the classic methods used for rubber mixing, like an internal mixer and an open two roll mill, which are soft mixing techniques. At low CNT rate in the matrix, the dispersion is controlled by two parameters such as the EPM matrix viscosity and the EVA concentration. The rheological and electrical properties varied abruptly when the CNT concentration is increased in the matrix. The low values obtained for this percolation threshold justify the use of EPM-EVA system. We have prepared an EPM-EVA master batch loaded with 20% of CNT and possessing very good conductive properties. We studied EPDM compound filled with carbon nanotubes, carbon black or the blend of both. We have demonstrated that the dilution of the master batch allows us to obtain a rubber filled with a constant Mooney viscosity but with an important impact on the vulcanization kinetics of elastomers. The synergistic effect between carbon black and carbon nanotubes has been shown on the mechanicals properties but not on the electrical ones.

L’intégration des communications optiques sur puce offre de vastes promesses en termes de performances et de réduction de la puissance consommée, les canaux optiques ne souffrant pas des nombreuses limitations des canaux métalliques. De plus, l’information codée optiquement permet d’atteindre des débits de données élevés par le biais du multiplexage en longueur d’onde. Afin de conserver la compatibilité avec les composants électroniques, les communications et composants optiques doivent s’intégrer dans la filière silicium. Cependant, ce dernier matériau ne permet pas d’envisager la réalisation de certaines fonctions optiques, en particulier la source laser. D’autres matériaux doivent ainsi être intégrés pour suppléer au silicium. Mes travaux de thèse portent sur l’intégration de nanotubes de carbone sur plate-forme silicium pour la photonique. Dans ces travaux, le potentiel des nanotubes de carbone pour la réalisation de sources optiques intégrées est exploré. Dans un premier temps, je proposerai des pistes de compréhension de l’apparition du gain optique dans les nanotubes de carbone semiconducteurs par analyse des temps de vie des excitons, mesurés en spectroscopie pompe-sonde. Ces temps de vie sont sensiblement rallongés lorsque la centrifugation des nanotubes de carbone, au cours de l’extraction, est poussée à des vélocités et des temps plus longs. Une explication envisagée est la réduction du nombre de défauts à la surface des nanotubes, ces défauts se comportant comme des centres de recombinaison non-radiatifs. D’autre part, une méthode efficace d’intégration des nanotubes de carbone sur guide d’onde silicium a été proposée. Cette méthode robuste et permet d’observer le couplage de la photoluminescence des nanotubes de carbone avec le mode optique du guide d’onde. Afin d’obtenir une interaction exaltée entre mode optique et nanotube de carbone, le couplage entre les nanotubes et différentes cavités photoniques, incluant microdisques, cavités Fabry-Pérot et micro-résonateurs en anneau, a été étudié. L’emploi en particulier de résonateurs en anneau permet d’observer la structuration de la photoluminescence des nanotubes de carbone par les modes de résonance de l’anneau. Différentes configurations ont été étudiées afin de compléter la compréhension des mécanismes de couplage : micro-photoluminescence, photoluminescence guidée et photoluminescence intégrée. / On-chip optical communication may increase drastically performances and consumption of communication systems. Indeed, optical channels do not face limitations that metallics interconnects do. Even better would be the achievable data rate due to the multiplexing possibility in optics. In order to keep compatibility with electronic devices, optical components and interconnects should be built in silicon. However, this material is not suitable for some optical function, such as laser sources. Thus, there is a need to integrate alternative materials to compensate for silicon weaknesses. My PhD work focuses on integration of carbon nanotube on silicon for photonics applications. In this work, potential use of carbon nanotube for light emission function is investigated. First, I will propose clue to understand the appearance of optical gain in semiconducting carbon nanotube. Such investigation is done by mean of pump-probe experiments, where the excitons lifetimes are measured. Those lifetimes slightly increase while centrifugation time and speed is increased, during the extraction process. A possible explanation is that defect-free carbon nanotubes are selected by the centrifugation process. In parallel, I worked on designing an efficient method to couple nanotubes photoluminescence with silicon waveguides. This method appears to be quite robust, and allows to observe coupling between the nanotube photoluminescence and the optical mode of the waveguide. In order to obtain a more intense interaction between the optical mode and carbon nanotubes, I investigated the coupling between carbon nanotubes and several photonic cavities, including microdisks, Fabry-Pérot cavities and ring resonators. Specifically, ring resonators allow to measure the photoluminescence of carbon nanotube structured by the resonant modes. Several configurations are studied to understand more in-depth the coupling mechanisms: micro-photoluminescence, guided photoluminescence and integrated photoluminescence.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-02T19:09:40Z No. of bitstreams: 1 RolffSpindola.pdf: 1912678 bytes, checksum: 00839e9b1b8a2b01a86770dd2561ec07 (MD5) / Made available in DSpace on 2017-06-02T19:09:40Z (GMT). No. of bitstreams: 1 RolffSpindola.pdf: 1912678 bytes, checksum: 00839e9b1b8a2b01a86770dd2561ec07 (MD5) Previous issue date: 2016-07-25 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / A novel platform for electroanalysis of isoniazid based on multi-walled carbon nanotube oxide and graphene oxide composite as support to iron phthalocyanine (MWCNTO-GO/FePc) has been developed. The FePc/MWCNTO-GO modified electrode is sensible for isoniazid, decreasing substantially its oxidation potential to + 200 mV vs. Ag/AgCl. Electrochemical and electroanalytical properties of the FePc/MWCNTO-GO modified electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy, and amperometry. The sensor presents better performance in 0,1 mol L-1 phosphate buffer at pH 7,4. Under optimized conditions, a linear response range from 5 μmol L-1 to 476 µmol L-1 was obtained with a sensitivity of 0,0225 μA L μmol-1. The limits of detection and quantification for isoniazid determination were 0,56 μmol L-1 and 1,88 μmol L-1, respectively. The relative standard deviation for 10 determinations of 100 μmol L-1 isoniazid was 2,5%. The sensor was successfully applied for isoniazid determination in artificial body fluids. / No presente trabalho é apresentado o desenvolvimento de uma nova plataforma para eletroanálise de isoniazida baseada em (MWCNTO-GO/FePc). O eletrodo modificado com FePc/MWCNTO-GO diminuiu sensivelmente o potencial de oxidação da isoniazida para +200 mV vs. Ag/AgCl. As propriedades eletroquímicas e eletroanalíticas do eletrodo modificado com FePc/MWCNTO-GO foram investigadas por voltametria cíclica, espectroscopia de impedância eletroquímica, microscopia eletroquímica de varredura, e amperometria. O sensor apresentou melhor desempenho em tampão fosfato 0,1 mol L-1 com pH 7,4. Sob condições otimizadas uma faixa de resposta linear de 5 μmol L-1 a 476 µmol L-1 foi obtida com uma sensibilidade de 0,0225 μA L μmol-1. O limite de detecção e quantificação para a isoniazida foram determinados como sendo 0,56 μmol L-1 e 1,88 μmol L-1, respectivamente. O desvio padrão relativo para 10 determinações de 100 μmol L-1 de isoniazida foi de 2,5%. O sensor foi aplicado com sucesso para determinação de isoniazida em fluidos corporais artificiais.

The growing applications for IoT devices have caused an increase in the study of low power consuming circuit design to meet the requirement of devices to operate for various months without external power supply. Scaling down the conventional CMOS causes various complications to design due to CMOS properties, therefore various non-conventional CMOS design techniques are being proposed that overcome the limitations. This thesis focuses on some of those emerging and novel low power design technique namely Adiabatic logic and low power devices like Magnetic Tunnel Junction (MTJ) and Carbon Nanotube Field Effect transistor (CNFET). Circuits that are used for large computations (multipliers, encryption engines) that amount to maximum part of power consumption in a whole chip are designed using these novel low power techniques.

In this work, gadolinium-based carbon nanocapsules are developed as a novel nanotechnology that addresses the shortcomings of current diagnostic and therapeutic methods of stem cell-based cardiomyoplasty. With cardiovascular disease (CVD) responsible for approximately 30% of deaths worldwide, the growing need for improved cardiomyoplasty has spurred efforts in nanomedicine to develop innovative techniques to enhance the therapeutic retention and diagnostic tracking of transplanted cells. Having previously been demonstrated as a high-performance T1-weighted magnetic resonance imaging (MRI) contrast agent, Gadonanotubes (GNTs) are shown for the first time to intracellularly label pig bone marrow-derived mesenchymal stem cells (MSCs). Without the use of a transfection agent, micromolar concentrations of GNTs deliver up to 10^9 Gd(III) ions per cell, allowing for MSCs to be visualized in a 1.5 T clinical MRI scanner. The cellular response to the intracellular incorporation of GNTs is also assessed, revealing that GNTs do not compromise the viability, differentiation potential, or phenotype characteristics of the MSCs. However, it is also found that GNT-labeled MSCs exhibit a decreased response to select cell adhesion proteins and experience a non-apoptotic, non-proliferative cell cycle arrest, from which the cells recover 48 h after GNT internalization. In tandem with developing GNTs as a new stem cell diagnostic agent, this current work also explores for the first time the therapeutic application of the magnetically-active GNTs as a magnetic facilitator to increase the retention of transplanted stem cells during cardiomyoplasty. In vitro flow chamber assays, ex vivo perfusion experiments, and in vivo porcine injection procedures all demonstrate the increased magnetic-assisted retention of GNT-labeled MSCs in the presence of an external magnetic field. These studies prove that GNTs are a powerful ‘theranostic’ agent that provides a novel platform to simultaneously monitor and improve the therapeutic nature of stem cells for the treatment of CVD. It is expected that this new nanotechnology will further catalyze the development of cellular cardiomyoplasty and other stem cell-based therapies for the prevention, detection, and treatment of human diseases.

Quasicrystalline compounds (QC) have been shown to have lower friction compared to other structures of the same constituents. The abscence of structural interlocking when two QC surfaces slide against one another yields the low friction. To use QC as low-friction coatings in combustion engines where hydrocarbon-based oil lubricant is commonly used, knowledge of how a film of lubricant forms on the coating is required. Any adsorbed films having non-quasicrystalline structure will reduce the self-lubricity of the coatings. In this manuscript, we report the results of simulations on thin films growth of selected hydrocarbons and rare gases on a decagonal Al$_{73}$Ni$_{10}$Co$_{17}$ quasicrystal (d-AlNiCo). Grand canonical Monte Carlo method is used to perform the simulations. We develop a set of classical interatomic many-body potentials which are based on the embedded-atom method to study the adsorption processes for hydrocarbons. Methane, propane, hexane, octane, and benzene are simulated and show complete wetting and layered films. Methane monolayer forms a pentagonal order commensurate with the d-AlNiCo. Propane forms disordered monolayer. Hexane and octane adsorb in a close-packed manner consistent with their bulk structure. The results of hexane and octane are expected to represent those of longer alkanes which constitute typical lubricants. Benzene monolayer has pentagonal order at low temperatures which transforms into triangular lattice at high temperatures. The effects of size mismatch and relative strength of the competing interactions (adsorbate-substrate and between adsorbates) on the film growth and structure are systematically studied using rare gases with Lennard-Jones pair potentials. It is found that the relative strength of the interactions determines the growth mode, while the structure of the film is affected mostly by the size mismatch between adsorbate and substrate's characteristic length. On d-AlNiCo, xenon monolayer undergoes a first-order structural transition from quasiperiodic pentagonal to periodic triangular. Smaller gases such as Ne, Ar, Kr do not show such transition. A simple rule is proposed to predict the existence of the transition which will be useful in the search of the appropriate quasicrystalline coatings for certain oil lubricants. Another part of this thesis is the calculation of phase diagram of Fe-Mo-C system under pressure for studying the effects of Mo on the thermodynamics of Fe:Mo nanoparticles as catalysts for growing single-walled carbon nanotubes (SWCNTs). Adding an appropriate amount of Mo to Fe particles avoids the formation of stable binary Fe$_3$C carbide that can terminate SWCNTs growth. Eventhough the formation of ternary carbides in Fe-Mo-C system might also reduce the activity of the catalyst, there are regions in the Fe:Mo which contain enough free Fe and excess carbon to yield nanotubes. Furthermore, the ternary carbides become stable at a smaller size of particle as compared to Fe$_3$C indicating that Fe:Mo particles can be used to grow smaller SWCNTs. / Dissertation

This study presents near-field electrospinning (NFES) on flat and hollow cylindrical process to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF)/ multi-walled carbon nanotube (MWCNT) piezoelectric nanofibers. Then the mechanical properties of fibers were measured. PVDF is a potential piezoelectric polymer material combining desirable mechanical, thermal, electrical properties with excellent chemical resistance. The existing researches mostly focused on piezoelectric thin film process. However, the research of characteristic about piezoelectric fiber is little. The methods of measurement of the mechanical properties (Young¡¦s modulus, hardness, and tensile strength¡Belongation) of the electrospun PVDF/MWCN composite nanofiber were carried out by using nano-indention test (MTS Nanoindenter Windows XP System) and tensile test (Microforce Testing System). By setting electric field (1¡Ñ107 V/m), rotating velocity (900 rpm) of the hollow cylindrical glass tube on a motion X-Y stage (2 mm/sec) and PVDF solution concentration (16 wt%), and MWCNT (0.03 wt%), in-situ electric poling, mechanical stretching and morphology of PVDF nanofiber were demonstrated. After the experiments of nano-indention test and tensile strength test, it is suggested that the good mechanical properties in NFES on cylindrical process. The results show that the mechanical properties of composite nanofiber are better than the conventional NFES process. The Young¡¦s modulus of 16% PVDF fiber prepared by cylindrical process is 0.89 GPa and hardness is 26.5 MPa. The mechanical properties were increased 56.2% and 49.4% after adding 0.03% of MWCNT, corresponding to 1.39 GPa and 39.6 MPa. The tensile strength was increased 32.7% and elongation at breaking point was increased 35% after adding 0.03% MWCNT.

The present work provides a micromechanics approach based on the generalized self-consistent composite cylinders method as a non-Eshelby approach towards for assessing the impact of carbon nanotubes on the multi-functional nature of nanocom-posites in which they are a constituent. Emphasis is placed on the effective elastic properties as well as electrical and thermal conductivities of nanocomposites con-sisting of randomly oriented single walled carbon nanotubes in epoxy. The effective elastic properties of aligned, as well as clustered and well-dispersed nanotubes in epoxy are discussed in the context of nanotube bundles using both the generalized self-consistent composite cylinders method as well as using computational microme-chanics techniques. In addition, interphase regions are introduced into the composite cylinders assemblages to account for the varying degrees of load transfer between nanotubes and the epoxy as a result of functionalization or lack thereof. Model pre-dictions for randomly oriented nanotubes both with and without interphase regions are compared to measured data from the literature with emphasis placed on assessing the bounds of the effective nanocomposite properties based on the uncertainty in the model input parameters. The generalized self-consistent composite cylinders model is also applied to model the electrical and thermal conductivity of carbon nanotube-epoxy nanocomposites. Recent experimental observations of the electrical conductivity of carbon nanotube polymer composites have identified extremely low percolation limits as well as a per-ceived double percolation behavior. Explanations for the extremely low percolation limit for the electrical conductivity of these nanocomposites have included both the creation of conductive networks of nanotubes within the matrix and quantum effects such as electron hopping or tunneling. Measurements of the thermal conductivity have also shown a strong dependence on nanoscale effects. However, in contrast, these nanoscale effects strongly limit the ability of the nanotubes to increase the thermal conductivity of the nanocomposite due to the formation of an interfacial thermal resistance layer between the nanotubes and the surrounding polymer. As such, emphasis is placed here on the incorporation of nanoscale effects, such as elec-tron hopping and interfacial thermal resistance, into the generalized self-consistent composite cylinder micromechanics model.

A variety of experiments were carried out to study the dispersion and microstructure of carbon nanotubes in aqueous suspensions and polymer composites with the goal to improve the electrical conductivity of the composites containing nanotubes. Epoxy composites containing covalently and noncovalently functionalized nanotubes were compared in terms of electrical and mechanical behavior. Covalent functionalization of nanotubes is based on chemical attachments of polyethylenimine (PEI) whereas noncovalent functionalization takes place through physical mixing of nanotubes and PEI. The electrical conductivity is reduced in composites containing covalently functionalized nanotubes due to damage of the tube?s conjugated surface that reduces intrinsic conductivity. Conversely, the mechanical properties are always better for epoxy composites containing covalently functionalized nanotubes. Clay particles were used as a rigid dispersing aid for nanotubes in aqueous suspensions and epoxy composites. When both nanotubes and clay were introduced into water by sonication, the suspension is stable for weeks, whereas the nanotubes precipitate almost instantly for the suspension without clay. In epoxy composites, nanotubes form separated clusters of aggregation, whereas a continuous threedimensional nanotube network is achieved when clay is introduced. Electrical conductivity of the epoxy composite is shown to significantly improve with a small addition of clay and the percolation threshold is simultaneously decreased (from 0.05 wt% nanotubes, when there is no clay, to 0.01 wt% when 2 wt% clay is introduced). The addition of clay can also improve the mechanical properties of the composites, especially at higher clay concentration. Weak polyelectrolytes (i.e., pH-responsive polymers) were also studied for their interaction with nanotubes and the electrical properties of the dried composite films. When dispersed by sonication, Nanotubes show pH-dependent dispersion and stability in poly(acrylic acid) water solution, as evidenced by changes in suspension viscosity and cryo-TEM images. The nanotube suspensions were then dried under ambient conditions and the composite films exhibit tailorable nanotube dispersion as a function of pH. The percolation threshold and maximum electrical conductivity are reduced when the pH is changed from low to high. Some other pH-responsive polymers were also studied, but their pH-dependent viscosity and conductivity were not as large or reversible as poly(acrylic acid).