Cette thèse s’inscrit dans le cadre du développement de nouveaux matériaux composites multifonctionnels, permettant de remplacer l’aluminium en tant qu’élément constituant le packaging de l’électronique embarquée dans les avions, afin de rendre ces derniers plus légers. L’association d’un polymère mécaniquement résistant avec des nano-charges conductrices est une alternative prometteuse. Cette thèse concerne l’étude du procédé de Dépôt Chimique à partir d’une phase Vapeur (CVD) en lit fluidisé pour déposer des métaux conducteurs, tels que le fer et le cuivre, à la surface de nanotubes de carbone multi-parois (MWCNTs) produits industriellement (Arkema Graphistrength®C100), enchevêtrés en pelotes poreuses de 388 μm de diamètre. Tout d’abord, afin d’augmenter la réactivité de surface des nanotubes, un procédé d’oxydation en lit fluidisé a été étudié à température ambiante, à partir de plusieurs mélanges gazeux à base d’ozone. Les diverses analyses réalisées (MET, spectroscopie IR, XPS,..) montrent que des groupements chimiques de type hydroxyl, acide carboxylique, éther, … sont greffés de façon uniforme sur toute la surface externe des MWCNTs et que leurs parois externes sont aussi gravées de façon modérée et localisée. Au final, il apparait que les défauts créés et les fonctions oxygénées greffées ont permis d’accroitre le nombre de sites de nucléation sur la surface des nanotubes et donc la masse de métal déposé. Le dépôt de fer à partir de ferrocène Fe(C5H5)2 a été étudié à haute température (entre 400 et 650°C), sous différentes ambiances gazeuses (azote, hydrogène, air, vapeur d’eau). Les analyses réalisées (MEB-FEG, DRX, MET, ICP-MS, ...) montrent un dépôt uniforme du bord jusqu’au coeur des pelotes, de nanoparticules à base de carbure de fer Fe3C prisonnières de l’enchevêtrement des nanotubes. La présence d’hydrogène a permis de minimiser la formation parasite de nano-objets (tubes et fibres). Le dépôt de cuivre à partir d’acétylacétonate de cuivre (II) Cu(C5H7O2)2 a été étudié entre 250 et 280°C sous hydrogène. Les caractérisations réalisées indiquent que des nanoparticules de Cu pur ont été déposées sur l’ensemble des parois externes des MWCNTs, du bord au coeur des pelotes. L’ensemble des résultats obtenus démontre que le procédé de CVD en lit fluidisé est capable de déposer de façon uniforme des métaux à la surface de nanotubes de carbone enchevêtrés en pelotes poreuses, pour des conditions opératoires spécifiquement choisies. / This Ph.D project is part of the development of new composite multi-functional materials allowing replacing aluminum in the on-board electronic packaging of airplanes, to make them lighter. The combination of a polymer mechanically resistant with conductive nano-fillers is a promising alternative. The thesis concerns the study of the Fluidized Bed Chemical Vapor Deposition (CVD) process of conductive metals, such as iron and copper, on the surface of industrial multi-walled carbon nanotubes (MWCNTs, Arkema Graphistrength®C100) tangled in porous balls of 388 μm in diameter. First, in order to increase the surface reactivity of nanotubes, an oxidation process in fluidized bed has been studied at room temperature, from several gaseous mixtures containing ozone. The various analyses (TEM, IR spectroscopy, XPS, …) show that hydroxyl, carboxylic acid, ether, … chemical bonds are grafted uniformly on all the outer surface of MWCNTs and that their outer walls are locally and moderately etched. At the end, it appears that the created defects and the oxygen containing bonds have allowed to increase the number of nucleation sites on the nanotubes surface and then the weight of the deposited metal. The iron deposit from ferrocene Fe(C5H5)2 has been studied at high temperature (between 400 and 650°C) under different gaseous atmospheres (nitrogen, hydrogen, air, water vapor). The analyses (FEG SEM, XRD, TEM, ICP-MS, ...) show a uniform deposit from the outer part to the center of the balls, of nanoparticles containing iron carbide Fe3C. The presence of hydrogen has allowed minimizing the parasitic formation of nano-objects (tubes and fibers). The copper deposition from copper (II) acetylacetonate Cu(C5H7O2)2 has been studied at 250-280°C under hydrogen. The characterizations indicate that nanoparticles of pure copper have been deposited on all the MWCNT outer walls, from the outer part to the center of the balls. The whole results obtained prove that the Fluidized Bed CVD process is able to deposit uniformly metals on the outer surface of MWCNTs tangled in porous balls, for specifically chosen operating conditions.

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.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A utilizaÃÃo de vigas laminadas de parede fina nas Engenharias AeronÃutica, Civil, MecÃnica e Naval tem crescido bastante nos Ãltimos anos, devido a suas elevadas relaÃÃes rigidez/peso e resistÃncia/peso. Esses elementos estruturais normalmente apresentam paredes finas devido à alta resistÃncia dos materiais compÃsitos. Outra caracterÃstica importante à que, mesmo sem apresentar grandes deformaÃÃes e sem que o limite elÃstico do material seja ultrapassado, estas vigas apresentam comportamento nÃo linear geomÃtrico devido à sua elevada esbeltez, acarretando em grandes deslocamentos e rotaÃÃes. Dependendo da laminaÃÃo utilizada, as vigas de materiais compÃsitos podem apresentar diversos acoplamentos entre esforÃos e deformaÃÃes, tornando a sua anÃlise bem mais complexa do que a anÃlise de vigas de material isotrÃpico. Neste trabalho, foram desenvolvidos dois elementos finitos de pÃrtico espacial para anÃlise nÃo linear geomÃtrica de vigas laminadas de parede fina. As propriedades seccionais da viga sÃo avaliadas atravÃs de teorias de vigas laminadas de parede fina apropriadas, em que desprezam-se os efeitos do empenamento e do cisalhamento transversal. Tais teorias de vigas laminadas conduzem a uma matriz constitutiva 4x4, onde diferentes nÃveis de acoplamento entre esforÃos e deformaÃÃes de viga sÃo considerados, por exemplo, pode-se obter uma matriz constitutiva diagonal ou cheia. A abordagem corrotacional independente do elemento à utilizada para o tratamento de grandes deslocamentos e rotaÃÃes de corpo rÃgido no espaÃo. No Ãmbito local, sÃo utilizados dois elementos, um baseado na teoria linear e outro na descriÃÃo Lagrangeana Total. O tratamento matemÃtico das grandes rotaÃÃes no espaÃo à realizado por meio do tensor das rotaÃÃes (fÃrmula de Rodrigues), juntamente com o conceito do pseudovetor. As implementaÃÃes dos elementos finitos propostos neste trabalho sÃo realizadas no software de cÃdigo aberto FAST. A metodologia de trabalho segue o roteiro clÃssico de mÃtodos computacionais, incluindo formulaÃÃo, implementaÃÃo, verificaÃÃo e validaÃÃo dos resultados. A verificaÃÃo à realizada atravÃs dos modelos tridimensionais de elementos finitos de casca e sÃlido desenvolvidos no software comercial ABAQUS. A validaÃÃo à realizada por meio da comparaÃÃo com resultados de ensaios experimentais encontrados na literatura. No que diz respeito à avaliaÃÃo das propriedades seccionais, pode-se verificar uma Ãtima concordÃncia entre as teorias de vigas laminadas adotadas neste trabalho e os resultados numÃricos e de ensaios experimentais, para todas as laminaÃÃes e carregamentos considerados. No caso dos elementos de pÃrtico espacial, verificou-se uma Ãtima concordÃncia entre os resultados dos elementos finitos propostos neste trabalho e os resultados analÃticos e computacionais disponÃveis na literatura. Observa-se tambÃm que o elemento baseado na descriÃÃo Lagrangeana à mais eficiente do que o elemento baseado na teoria linear no que tange à capacidade de apresentar uma resposta satisfatÃria com uma malha menos refinada. / The use of thin walled laminate beams in Aeronautical, Civil, Mechanical and Naval Enginee- ring is increasing in the last years. This is due to their high stiffness/weight and strength/weight ratios. Composite beams and other structural elements tend to have thin walls due to the elevated strength of the material. Other important aspect is that, even without reaching large strains and without overcoming the elastic limit of the material, such beams present geometric nonlinear behavior due to high their slenderness, leading to large displacements and rotations. Depen- ding on the composite layup, the beams of composite materials can present several couplings between generalized stresses and strains, requiring a more complex analysis procedure when compared to isotropic beams. In this work, two three-dimensional space frame finite elements that can be used to analyze composite thin-walled beams subjected to geometric non-linearity were developed. The cross-section properties of the beams are evaluated through suitable thin walled beam theories, where the effects of the warping and transverse shear are neglected. Such theories yield a 4x4 constitutive matrix for the laminate and different levels of coupling between generalized stresses and strains can be considered. Depending of such couplings, the constitu- tive matrix can either be full or diagonal. The element independent corotational approach was used in order to consider large displacaments and rigid body rotations in space. In the local coordinate system, two elements are used, one based on the linear strain theory and the other on the Total Lagrangian formulation. The mathematical treatment of the large rotations in the space is performed by means of the rotation tensor (Rodriguesâs formula) in conjunction with the concept of the pseudovector. The computational implementations of the two finite elements proposed in this work were done in the open source software FAST ( Finite Element Analysis Tool ). The methodology used follows the classical steps used in computational methods, in- cluding formulation, implementation, verification and validation of results. Such verification is accomplished through shell and solid three-dimensional finite element models developed in the ABAQUS commercial software. The validation is performed by means of comparison with the experimental results found in literature. Regarding the evaluation of cross-sectional properties, one can observe a good agreement between the laminated beam theories adopted in this work and numerical and experimental results for all composite layups and load conditions conside- red. In the case of space frame elements, a good agreement is obtained between the results of finite elements proposed in this work and the analytical and computational results available in the literature. It is also observed that the element based on the Lagrangian formulation is more efficient than the element based on the linear theory regarding the ability to provide a satisfatory response with a less refined mesh

Ce travail de thèse se concentre sur l’étude du comportement dynamique des tubes minces durant leur usinage par tournage et notamment sur la survenue du broutement régénératif. L’étude de l’usinage de ce type de pièce est pertinente car ces pièces font l’objet d’une large diffusion dans divers domaines industriels tels que la construction aéronautique (notamment moteurs), la construction navale, la production de fusées. Ces pièces ayant une faible rigidité, il est fréquent que des vibrations indésirables se produisent en cours d’usinage. Il est donc intéressant d’être à même de les prédire pour les éviter.L’approche proposée vise à permettre un choix rapide et efficace des conditions de coupe, et notamment des profondeurs de passe, pour cette opération d’usinage. Pour cela nous proposons de mettre en place un modèle mécanique analytique du tube (modèle de coque mince utilisant un nombre réduit de degrés de liberté) de manière à réduire les coûts numériques et à faciliter l’analyse du phénomène. L’impact de la taille du modèle sur les résultats est étudié (nombre de formes propres) ainsi que de la prise en compte de l’enlèvement de matière (évolution du comportement dynamique) et du déplacement de l’outil. Afin de valider l’approche une expérience a été mise en place et est également présentée dans ce mémoire. / This work focuses on the study of the dynamic behavior of thin tubes during their machining by turning and gives particular emphasis on the occurrence of regenerative chatter. The study of machining of this type of workpiece is relevant because they are widely used in various industrial fields such as aircraft construction (including engines), shipbuilding, rocket production. As these parts have low rigidity, it is common that undesirable vibrations occur during machining. It is therefore of interest to be able to predict them in order to avoid them.The proposed approach is designed to enable a fast and efficient selection of cutting conditions, including cutting depths for this machining operation. We thus propose to elaborated an analytical model for the dynamics of the tube (thin shell based model using a reduced number of degrees of freedom) to reduce the numerical costs and to facilitate the analysis of the phenomenon. The impact of the size of the model on the results is studied (number of shape functions), as well as the impact of material removal (evolution of the dynamic behavior) and of the motion of the tool. An experiment, presented in this thesis, was also set up in order to validate the approach.

In the last three decades carbon nanomaterials such as fullerenes, carbon nanotubes and graphene have attracted significant attention from the scientific community due to their unique electronic, optical, thermal, mechanical and chemical properties. Among them carbon nanotubes and graphene have been used in numerous applications for future nanoelectronics, biochemical sensors and energy harvesting technologies due to their unique properties including exceptionally high electronic conductivity and mechanical strength. Carbon nanotubes are cylindrical structures and considered to be large mesoscopic molecules with high aspect ratios. Graphene is a single atomic layer of crystalline graphite and prepared by stripping layers off the graphite using Scotch tape. Apart from this scotch tape method, chemical ex-foliation and reduction of graphite oxide produces large amounts of reduced graphene oxide which has similar properties as graphene. This thesis reports on the biosensors made of reduced graphene oxide and single walled carbon nanotubes based on their electronic properties. We also demonstrate the changes in electronic properties of single walled carbon nanotubes due to interactions with dendrimer molecules. Finally, the yielding and flow behaviour of graphene oxide nematic gel are discussed. Chapter 1 gives a general introduction about the preparation and characterization along with the electronic properties of the systems studied in this thesis, namely graphene oxide, reduced graphene oxide and single walled carbon nanotubes. We have also discussed about the experimental techniques such as Raman, UV-visibe and infrared spectroscopy, atomic force and scanning tunneling microscopy and different types of rheometers used in this thesis work. In Chapter 2, we discuss top-gated field effect transistor characteristics of the devices made of reduced graphene oxide monolayer by dielectrophoresis. Raman spectrum of RGO flakes shows a single 2D band at 2687 cm 1, characteristic of a single layer graphene. The two probe current - voltage measurements of RGO flakes, deposited in between the patterned electrodes using a.c. dielectrophoresis show ohmic behavior with a resistance of 37kΩ. The temperature dependence of the resistance (R) of RGO measured between temperatures 305K to 393K yields the temperature coefficient of resistance of -9.5 10 4/K. Ambipolar nature of graphene flakes is observed upto a doping level of 6 1012/cm2 and carrier mobility of 50cm2/V-sec. The source - drain current characteristics shows a tendency of current saturation at high source - drain voltage which is analyzed quantitatively by a diffusive transport model. In Chapter 3, We demonstrate the detection of glucose molecules by using reduced graphene oxide (RGO) and aminophenylboronic acid (APBA) complex with detection limit of 5 nM. APBA functionalized RGO (APBA-RGO) flakes, prepared by stirring the aqueous GO suspension in the presence of APBA molecules at 100◦C, were used as conducting channel in our field effect transistor (FET) devices. The APBA-RGO complex formation was confirmed by atomic force microscopy (AFM), x - ray photoelectron, Raman and UV-visible spectroscopic studies. Detection of glucose molecules was carried out by monitoring the changes in electrical conductance of the APBA-RGO flake in the FET device. FET devices made of non-covelently functionalized APBA-RGO complex (nc-APBA-RGO) exhibited enhanced sensitivity over the devices made of covalently functionalized APBA-RGO complex (c-APBA-RGO). Change in normalized conductance in the FET devices made of nc-APBA-RGO flakes ( 85%) is 4 times more than that of in the devices made of c-APBA-RGO flakes in response to aqueous glucose solution with different concentrations. Specificity of APBA-RGO complex to glucose was proved from the observation of negligible change in electrical conductance of the FET devices made of nc-APBA-RGO complex after exposure to 10 mM lactose solution. Chapter 4 reports unipolar resistive switching in ultrathin films of chemically produced graphene (reduced graphene oxide) and multiwalled carbon nanotubes. The two - terminal devices with yield > 99% are made at room temperature by forming continuous films of graphene of thickness 20 nm on indium tin oxide coated glass electrode, followed by metal (Au or Al) deposition on the lm. These memory devices are non - volatile, rewritable with ON/OFF ratios up to 105 and switching times up to 10 s. The devices made of MWNT films are rewritable with ON/OFF ratios up to 400. The resistive switching mechanism is proposed to be nanogap formation. In the first part of Chapter 5, we study the interactions between SWNT and PETIM dendrimer by measuring the quenching of inherent fluorescence of the dendrimer. Also, the dendrimer - nanotube binding results in the increased electrical resistance of the hole-doped SWNT due to charge transfer interaction between the dendrimer and the nanotube. This charge transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. Experimental studies were supplemented by all atom molecular dynamics simulations to provide a microscopic picture of the dendrimer - nanotube complex. The complexation was achieved through charge - transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen and n-propyl moieties of the dendrimer. We also studied the effect of acidic and neutral pH conditions on the binding affinities. In the second part, we show that SWNT decorated with sugar functionalized PETIM dendrimer is a very sensitive platform to quantitatively detect carbohydrate recognizing proteins, namely, lectins. The changes in electrical conductivity of SWNT in field effect transistor device due to carbohydrate - protein interactions forms the basis of this study. The mannose sugar attached PETIM dendrimers undergo charge - transfer interactions with the SWNT. The changes in the conductance of the dendritic sugar functionalized SWNT after addition of lectins in varying concentrations were found to follow the Langmuir type isotherm, giving the concanavalin A (Con A) - mannose affinity constant to be 8.5 106 M-1. The increase in the device conductance observed after adding 10 nM of Con A is same as after adding 20 µM of a non - specific lectin peanut agglutinin, showing the high specificity of the Con A - mannose interactions. The specificity of sugar-lectin interactions was characterized further by observing significant shifts in Raman modes of the SWNT. Chapter 6 reports the metal to semiconductor transition in metallic single-wall carbon nanotubes (SWNT) due to the wrapping of mannose attached poly (propyl ether imine) dendrimer (DM) molecule. Scanning tunneling spectroscopic (STS) measurements and ionic liquid top gated field effect transistor (FET) characteristics of the nanotube-dendrimer complex gives a band gap of 0.42eV, close to the E11 energy gap between the first van Hove singularities of 1.7nm diameter semiconducting nanotubes. The absence of Breit-Wigner-Fano (BWF) component in G band in the Raman spectrum of the nanotube-dendrimer complex corroborates the semiconductor nature of the tubes after wrapping with the dendrimer molecules. Dendrimer molecule breaks the symmetry in metallic SWNT by wrapping around it through the charge transfer interactions. In the first part of Chapter 7, we demonstrate a rigidity percolation transition and the onset of yield stress in a dilute aqueous dispersion of graphene oxide platelets (aspect ratio 5000) above a critical volume fraction of 3.75x10-4 with a percolation exponent of 2.4 ± 0.1.The viscoelastic moduli of the gel at rest measured as a function of time indicates the absence of structural evolution of the 3D percolated network of disks. However, a shear-induced aging giving rise to a compact jammed state and shear rejuvenation indicating a homogenous flow is observed when a steady shear stress (σ ) is imposed in creep experiments. We construct a shear diagram (σ vs volume fraction ϕ) and the critical stress above which shear rejuvenation occurs is identified as the yield stress σ y of the gel. The minimum steady state shear rate ƴm obtained from creep experiments agrees well with the end of the plateau region in a controlled shear rate flow curve, indicating a shear localization below ƴm. A steady state shear banding in the plateau region of the flow curve observed in particle velocimetry measurements in a couette geometry confirms that the dilute suspensions of GO platelets form a thixotropic yield stress fluid (TYSF). In the second part, we report that the creep experiments on a nematic liquid crystalline suspension of Graphene Oxide platelets which was established recently as a TYSF exhibit two characteristic timescales Tc and Tf marking the onset of yielding, and a final steady state of flow respectively. We show that both Tc and Tf exhibit a power law dependence on the applied stress σ which can be linked to the steady state flow behaviour of a TYSF. The smooth transition from Andrade creep to the onset of flow with ƴ~ t 0.7 at a critical strain ƴc for different applied stresses, is well captured by the master curve for the creep compliance, obtained through a simple scaling of the creep times with either Tc or Tf . We propose that the absence of diverging timescales for onset of flow as σ→ yield stress σy from above, is a characteristic feature of TYSF. The thesis concludes with a summary of the main results and a brief account of the scope of future work described in Chapter 8.

Different carbon nanostructures have different properties and different applications. It is needed to synthesize good quality and also on large scale. From the point of industrial applications, highly productive and low cost synthesis method is very essential. Research has been done extensively on the intrinsic and individual properties of both single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWC-NTs) in the range of nanometer to micrometer length scale. The important question is how the properties change beyond this length scale and if they are used in group in the form of an array instead of the individual carbon nanotubes (CNTs). Some applications require large current output, large energy production etc. For such kind of applications, it becomes essential to use CNTs in large number in the form of arrays or array, instead of using large numbers of CNTs in individual level. Future nanotechnology scope requires large scale application using the very rich intrinsic properties of the CNTs and nanomaterials. Keeping these problems and challenges in front, this thesis work is devoted to the research of the large scale synthesis of mm long MWCNTs, having different morphology and studies on various physical properties of MWCNTs in the form of arrays. Synthesis of mm long aligned and buckled MWCNTs have been reported for the first time. Generally buckled CNTs were obtained by compressing the straight CNTs. Apart from this, different morphologies like, aligned straight, helical or coiled CNTs are also synthesized. Resistance of the individual CNT increases with the increase in length. Resistance versus length of an array of CNT also shows similar behaviour. The thermal conductivity of CNT array is observed to decrease with the increase of array diameter (diameter �100 µm). There are few reports of the similar behaviour with the experiments done on small diameter CNT arrays (diameter �100 nm). From these observations, it seems that in the arrays of CNT, their intrinsic individual property is preserved though the magnitudes are different. The conductance measurements done on buckled CNT array by compressing it to apply uniaxial strain, shows the conductance oscillation. This conductance oscillation seems to be originating from the band gap change due to strain when the CNTs bend during compression. Recent research focuses on the arrays of CNT as they can carry large current of the order of several milliamperes that make the arrays suitable in nanoscale electronics and in controlling macroscopic devices such as light emitting diodes and electromotors. Regarding this aspect, a part of this thesis work is devoted on the application of CNT array to field effect transistor (FET) and study of thermoelectric power generation using CNT arrays. The entire thesis is based on the works discussed above. It has been organized as follows: Chapter 1 deals with introduction about the different carbon nanostructures and different synthesis methods. A brief introduction about the different current-voltage (IV) characteristics of SWCNTs and MWCNTs, length and diameter dependence and effect of the mode of contacts, are given. Some applications of the array of CNTs like buckling effect on compression, stretching of CNT into the form of rope, and conduction change on compression are discussed. Application of CNT as FET, as a thermometer, and thermoelectric effect of CNT are discussed. The electromechanical effect of CNT is also discussed briefly. Chapter 2 deals with experimental setup for synthesis of different morphologies of carbon nanostructures. The samples are characterized using common characterization techniques like, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. A brief introduction about Raman Spectroscopy of CNT is given. Chapter 3 reports the unusual IV characteristics and breakdown of long CNT arrays. The current carrying ability and the threshold voltage as a function of array diameter are reported. The effect of the ambient like temperature and pressure are discussed. Chapter 4 deals with theoretical models to analyze the IV characteristics reported in Chapter 3. It has been shown that a set of classical equations are applicable to quantum structures and the band gap can be evaluated. Chapter 5 describes with application of CNT arrays as temperature sensors. It has been shown that CNT arrays of suitable diameters are used as temperature sensors after calibration. Chapter 6 reports the high current FET application of CNT arrays. Effects of temperature and ambient pressure are discussed. The type of the majority charge carrier is determined. Chapter 7 deals with application of CNT arrays as thermoelectric power generator to get large thermoelectric current. Effects of different array diameter are discussed. Modulation of thermoemf with gate voltage is discussed. The type of the majority charge carrier is determined. Chapter 8 reports the effect of compressive strain on buckled MWCNT arrays. Conductance is measured during the compression of the array. Quantum electromechanical conductance oscillation is observed. The structural changes are observed with SEM. Raman spectroscopic study supports the explanation of the effect. Chapter 9 provides the conclusion and overall summary of the thesis.

The thesis contains two parts. Part 1 describes the investigations on graphene and contains five sections. Section 1, gives a brief overview of graphene and other nanocarbons. The other four sections deal with various aspects of single-layer and few-layer graphene such as functionalization and solubilization, surface properties and gas adsorption, molecular charge transfer interaction and some properties and applications. Section 2 describes covalent and noncovalent functionalization and solubilization of few-layer graphene samples prepared by different methods as well as of single-walled carbon nanotubes (SWNTs). It includes covalent functionalization of graphene with organometallic reagents, noncovalent functionalization of graphene and SWNTs with surfactants as well as large aromatic molecules, and exfoliation of few-layer graphene by a water-soluble coronene carboxylate. Section 3 deals with surface properties and gas adsorption (mainly H2 and CO2) of few-layer graphenes. It is found that graphene samples with high surface area can adsorb even more than 3 wt% of H2 at high pressure which makes it promising material for gas-storage applications. Section 4 describes the molecular charge-transfer interaction of single and few-layered graphenes and SWNTs with different electron-donor and -acceptor molecules probed by both ITC measurements and Raman spectroscopy. Electron–acceptor molecules interact more strongly with graphene and SWNTs than the -donor molecules and nature of interaction of metallic SWNTs are different than the as-prepared ones. A Raman study of the interaction of single-layer graphene, prepared by micromechanical cleavage as well as chemical route, with an electron donor molecule such as tetrathiofulvalene (TTF) and an electron acceptor molecule such as tetracyanoethylene (TCNE) is examined. In Section 5, some properties and applications of graphene are discussed. These include fluorescence quenching phenomena observed with few-layer graphene samples on two fluorescent molecules such as coronene and perylene derivatives. Fabrication of a sensing device as well as of FETs prepared from doped and undoped few-layer and single-layer graphene samples forms part of this section. Part 2 of the thesis includes a brief introduction of hybrid open-framework material and synthesis, characterization and crystal structure of various open-framework metal carboxylates, starting with different transition and main group metals. The carboxylic acids used to form these frameworks vary such as simple aliphatic amino acids such as beta-alanine and aspartic acid or simple aliphatic hydroxyl carboxylic acid such as malic acid in its chiral and achiral forms or five-membered heterocyclic aromatic acid, such as imidazole dicarboxylic acid.

Orientadores: Júlio Roberto Bartoli, Elizabeth Grillo Fernandes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T08:51:19Z (GMT). No. of bitstreams: 1 Cecci_RicardoRodrigoRamos_M.pdf: 4182332 bytes, checksum: 4424cc557c439a1602d15a95921a2b25 (MD5) Previous issue date: 2013 / Resumo: Nanotubos de carbono (NTCs) apresentam características interessantes para aplicações em eletrodos transparentes. Quando dispersos em escala nanométrica são transparentes ao espectro da luz visível e são capazes de conduzir eletricidade após atingirem percolação em matrizes poliméricas isolantes. Neste trabalho, é descrito o uso de nanotubos de carbono de camadas múltiplas (NTCMs) na produção de filmes poliméricos flexíveis transparentes e condutores como alternativa ao uso do óxido de índio dopado com estanho (ITO) em células solares orgânicas. Os nanotubos foram dispersos e purificados em solução aquosa de dodecil sulfato de sódio (SDS) pelos processos de sonicação e centrifugação, e a dispersão monitorada por espectroscopia UV-Vis e potencial ?. Os nanocompósitos foram produzidos via polimerização in situ do monômero metacrilato de metila (MMA) na presença de 0 a 1% p/p NTCs e os filmes depositados através da técnica de revestimento por rotação a alta velocidade (spin coating). A reação de polimerização foi acompanhada pela calorimetria exploratória diferencial (DSC). Verificou-se que na presença de NTCs, a taxa de conversão do monômero é acelerada. A cinética de degradação térmica foi avaliada pelo método de Broido utilizando a análise termogravimétrica (TGA). Foi observado que os NTCs aumentam a estabilidade térmica do PMMA, retardando a degradação por despolimerização. Estudos por espectroscopia FT-IR mostraram uma banda de absorção em 1601 cm-1, (C=C), a qual não é característica do PMMA, indicando que os NTCs participam da polimerização do PMMA. Para concentrações de até 1% p/p de NTCs, os filmes PMMA/NTC apresentaram excelentes propriedades ópticas. Ou seja, baixo coeficiente de absorção, na ordem de 103 cm-1, altos valores de gap óptico (Eopt), entre 3,2 e 4,14 eV, e alta transparência por todo espectro visível, entre 88 e 93%. Nas mesmas concentrações, foi observada uma diminuição substancial na resistividade elétrica dos filmes em 8 ordens de grandeza (de 1016 para 108 ?/quadrado), comparados ao filme de PMMA puro. Entretanto, a faixa de resistividade alcançada ainda é típica de materiais isolantes. Estudos de otimização poderiam originar filmes PMMA/NTC como uma alternativa promissora para ITO em OPVs / Abstract: Carbon nanotubes (CNTs) have interesting features for applications in transparent electrodes. When dispersed at the nanoscale, they become transparent within the visible range and are able to conduct electricity after reaching the percolation threshold in an insulating polymer matrix. In this work, the use of multi-walled carbon nanotubes (MWCNTs) is described for the production of flexible transparent conducting polymer films as an alternative to the use of indium-tin oxide (ITO) in organic solar cells. The nanotubes were dispersed and purified in an aqueous solution of sodium dodecyl sulfate (SDS) by the process of sonication and centrifugation, and the dispersion monitored by UV-Vis spectroscopy and ? potential. The nanocomposites were produced via in situ polymerization of the monomer methyl methacrylate (MMA) in the presence of 0 to 1 %wt. of CNTs. The films were deposited by the spin-coating technique. The polymerization reaction was monitored by differential scanning calorimetry (DSC). It was found that in the presence of CNTs, the conversion rate of the monomer is accelerated. The kinetics of thermal degradation was measured according to the Broido's method by using thermogravimetric analysis (TGA). It was observed that CNTs increase the thermal stability of PMMA, slowing degradation by depolymerization. FT-IR data showed an absorption band at 1601 cm-1 (C = C), which is not characteristic of PMMA, indicating that the CNTs takes place in the polymerization of PMMA. For concentrations up to 1wt% of CNTs, the PMMA/CNT films had excellent optical properties, i.e., a low absorption coefficient in the order of 103 cm-1, wide optical gap (Eopt) between 3.2 and 4.14 eV, and high transparency within the whole visible range, between 88 and 93%. In the same concentrations, the electrical resistivity of the films dropped by 8 orders of magnitude (from 1016 to 108 ?/sqr), compared to the pure PMMA film. Even though this electrical resistivity value is typical of insulating materials, further optimization studies could provide PMMA/CNT films as a promising alternative to ITO in OPV / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

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This thesis concerns the technological processes of machining of thin-walled parts and the modification of said processes in dependence on the following interopera-tive measurement of the real dimensions of these parts. Within the theoretical part a research study of technological possibilities of measuring thin-walled parts and principles of probe programming are presented. In the main practical part of the the-sis a proposal of an experiment is described, which tests the individual technologi-cal steps and their influence on the quality of a prototype of the produced thin-walled part. Numerical (NC) codes are created using parametric programming, which are then used during the realization of the experiment itself. In the conclusi-on there are presented and discussed the results of measuring of the machined surfaces and the influence of correction paths, which should help to achieve a mo-re accurate production according to given dimensions. This experiment, however, has not met the expected results. That is why new procedures have been designed in order to create said paths, which can be used in a future realization of this expe-riment.