Individual carbon nanotubes have been theoretically and experimentally proven to be the strongest and stiffest materials discovered to date with tensile strengths ranging from 1-5 TPa and elastic modulus values as high as 150 GPa. In this work, the recent development of continuous sheets of CNTs, produced by Nanocomp Technologies Inc ., are investigated for their potential as reinforcement in polymer matrix composite (PMC) materials. The potential of these nanotube-based PMC materials have been reported by researchers at Florida State University (FSU). Through the use of mechanical stretching procedures to increase the alignment of the nanotubes within the CNT sheets, the tensile strength and Young's modulus of the composites in the FSU study averaged 3081 MPa and 350 GPa, respectively. These values are for composites fabricated from 40% stretched CNT sheets and are 48% and 107% improvements over composites fabricated from the pristine, unstretched CNT sheets. However, the test specimens used in the FSU study consisted of a single CNT ply and each coupon was individually stretched and cured for testing. Therefore, the process used to generate the coupons which exhibited these high mechanical properties would be difficult to scale to a usable size for aerospace structural components. In the current study, a scalable process has been developed in which 2-ply, 3" x 3" panels of CNT and resin composites are fabricated. An apparatus and methodology for mechanically stretching the CNT sheets used in these composite panels has also been developed. After initial testing was conducted with the CNT composites and the coupons exhibited significant elongation at failure, along with the absence of a linear elastic region, conventional test standards for material testing were deemed impractical. For this reason, new mechanical testing methodologies have been developed to determine the mechanical properties of specific strength and specific modulus of CNT-polymer composites. In order to obtain the maximum benefits of a fiber in any matrix in terms of stiffness and strength, it is preferable to align the high strength and stiffness fibers in the direction of loading. Given that these CNT sheets essentially consist of billions of short, discontinuous CNTs of 2-3mmin length, the process of mechanical stretching is used in an attempt to align these tubes in the direction of the applied tensile load. Here we have explored methodologies for stretching, fabricating, and mechanical testing. Having identified a process which seems viable, an examination into the effect of the mechanical stretching to increase the alignment of the nanotubes within the CNT sheets, and thus to increase the material properties of the 2-ply composites constructed from them, is conducted. In order to correlate the enhancements in the mechanical properties with the increased alignment of the CNTs, polarized Raman spectroscopy techniques have been used. Lastly, Scanning Electron Microscopy (SEM) is used to examine the effect of stretching on the pristine CNT sheet, as well as examine the fracture surfaces of failed test coupons to better characterize the failure modes. In this report, polarized Raman spectroscopy has been used to confirm the enhancedalignment of nanotubes within the CNT sheets through the used of a nematic order parameter. Unstretched sheets exhibit an order parameter of 0.07 and 0.09 for untreated and Acetone treated sheets, respectively. Upon stretching the untreated sheets to 45%, the order parameter increases to 0.1409 and, when stretched to 30%, Acetone treated sheets have an order parameter of 0.1518. During the mechanical testing of 2-ply composites fabricated from stretched CNT sheets, the effect of this increased alignment is made apparent. Untreated CNT sheets are used to fabricate 2-ply composites after being stretched and are compared to baseline values of panels fabricated using sheets which are not stretched. In the panels fabricated with PEI resin and 43% stretched, untreated CNT sheets, a 137% increase in average specific strength and a 44% increase in average specific modulus over the baseline panel is observed. For panels fabricated with BMI and 33% stretched, untreated CNT sheets, a 169% increase in average specific strength and 105% increase in average specific modulus is observed when compared to the baseline panel. These increases are evidence for the potential of mechanical stretching to align the nanotubes within the CNT sheets and bolster the mechanical properties of resulting CNT-polymer composites. / Master of Science

The mechanical behavior of discrete atoms has been studied with molecular dynamics whose computational time is proportional to the square of the number of atoms, O(N²). Recently, a faster algorithm, Atomic-scale Finite Element Method (AFEM) with computational time proportional to the number of atoms, O(N), had been developed. The main idea of AFEM, compared with conventional finite element method is to replace nodes with atoms and elements with electric forces between atoms. When interpreting a non-linear system, it is necessary to use an iteration scheme. A simulation of molecular dynamics based on the Verlet's method was conducted in order to validate AFEM in one dimension. The speed of AFEM was investigated in one and two dimensional atomic systems. The results showed that the computational time of AFEM is approximately proportional to the number of atoms, and the absolute computation time appears to be small. The frameworks of AFEM not only for multi-body potential but also pair potential are presented. Finally, AFEM was applied to analyze and interpret the mechanical behavior of a carbon nanotube and a quartz. The buckling behavior of carbon nanotube showed a good agreement with the results illustrated in the original literature. / Master of Science

The main motivation in this thesis is to compare the conformation and charge transport in conducting polymers and carbon nanotubes (CNTs) and to investigate those physical properties in their combined form of nanocomposites. It is known that both conducting polymers and carbon nanotubes are intrinsically 1-dimensional systems which consist of delocalized π-electrons. However, the main difference between these is the fact that flexibility of conducting polymers can be varied depending on the extent of conjugation while CNTs are rigid. Hence a comparison of electronic properties as correlated to their morphology has been carried out and their individual role in nanocomposites is further studied. The thesis consists of 6 chapters and appendix. Chapter 1 consists of brief introduction of general properties of both conducting polymers, CNTs and their nanocomposites. Chapter 2 deals with the sample preparation and experimental techniques used for the work. Chapter 3 elaborates on the conformational / structural studies on the systems. Chapter 4 focuses on the transport measurements to study the electronic properties of the samples. Chapter 5 reveals the magnetic properties of these systems which can be applied in technological devices. And chapter 6 gives the conclusion and future directions of the work being done. Chapter 1: Nanocomposites represent a guest-host matrix consisting of easily processible functionalized conjugated polymer as host, incorporating carbon nanotubes as fillers with versatile electronic and magnetic properties, which provide a wide range of technological applications. The conformation, charge dynamics as well as magnetic properties of these conducting polymers and carbon nanotubes, and various aspects of transport mechanism and spin dynamics present in the nanocomposite matrix are studied and presented in a consistent framework. Chapter 2: The multiwall carbon nanotubes (MWNTs) are grown by thermal chemical vapor deposition (CVD). The MWNTs are dispersed in solution of conducting polymers by ultrasonication and then the suspension is cast on glass substrate and slowly dried by moderate heating. Once dried completely, the free-standing films of thickness 15-25 μm are peeled off the substrate for measurements. The MWNTs, above a certain concentration, form an interconnected network in the 3-dimensional polymer matrix, following percolation mechanism. The disorder is brought into the system mainly by bundling of tubes and bundle intersections. The morphology and conformation of the samples are studied by SEM, TEM and small angle X-ray scattering (SAXS) techniques. Chapter 3: Small angle X-ray scattering (SAXS) studies in polymeric systems are carried out to probe local nanoscale morphology at various length scales to show the correlation among conformation and assembly of chains. Small angle X-ray scattering (SAXS) studies are carried out in poly [2-methoxy5-(2’–ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) solution of varying conjugation lengths as well as different solvents. By increasing the extent of πconjugation from 30 to 100 %, the persistence length increases by a factor of three. Moreover, a pronounced second peak in the pair distribution function is observed in fully conjugated chain, at larger length scales which indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. The chain assembly and aggregation are further studied for suspensions of MWNTs in polyethylene dioxythiophene-polystyrene (PEDOT-PSS) with aqueous medium and DMSO (dimethyl sulphoxide). The SAXS profile of MWNT dispersion in aqueous PEDOT-PSS clearly show rigid-rod feature of the individual nanotubes evident by the q-1 behavior at short ranges. The crossover from q-1 to q-2 in the longer range further suggest that the suspension consists of individual nanotubes, nanotubes bundles and aggregates that give rise to a 3-dimensonal meshwork of intersecting tubes and ropes. For the MWNT dispersion in PEDOT-PSS with DMSO, however, such q-1 behavior is absent; which evidently shows that the rods are not isolated in the solution and are rather agglomerated. How these conformations affect the electrical and magnetic properties of these systems are studied further in Chapter 4. Chapter 4: Transport mechanism in single wall carbon nanotubes (SWNT), MWNT pellets, and nanocomposite films of MWNT and PEDOT-PSS is studied. The positive and negative magnetoresistance (MR) data in various SWNT samples are analyzed by taking into account the electron-electron interaction (EEI) contribution, in addition to the weak localization (WL) regime. The contribution from EEI to the total MR is confirmed from the universal scaling of MC relation showing that EEI plays a significant role at higher fields and lower temperatures. Intrinsic parameters like inelastic scattering length extracted for barely metallic sample follows the T-3/4 dependence due to inelastic electron-electron scattering in the dirty limit. Conductivity and magnetoresistance (MR) measurements on nanocomposite films with varying MWNT content (0.03 - 3 %) are performed at a field range 0-11 Tesla, and temperature range 1.3–300 K. The temperature dependence of resistance above 4 K suggests a Coulomb-gap variable range hopping (CG-VRH) transport in the network. Alhough solely negative MR (~ 5-6 %) is observed for pristine MWNT pellets; the nanocomposite films show a combination of large negative MR (~ 80 %) at T < 4 K, and a comparatively weaker positive MR (~ 30 %) for T > 4 K. This suggest that there are two mechanism interplaying and dominant at different temperature regimes which can be explained by the mechanism of transport of the charge carriers of MWNT intervened by that of the polymer matrix. In conclusion how the individual properties of conducting polymer and carbon nanotubes contribute to the unique electronic and conformational properties in their nanocomposites is framed in this investigation. Chapter 5: Magnetic properties of the pristine MWNTs as well as metal nanowires of nickel, nickel-iron (NiFe), nickel-iron-cobalt (NiFeCo) encapsulated in the MWNTs are studied using superconducting quantum interference device (SQUID) magnetometer. A typical example of Ni nanowires encapsulated in MWNT (Ni-MWNT) is taken and the results are compared to other forms of nickel (bulk, nanorod cluster, nanowire) to see the effect of size, shape and environment on the magnetic kproperties. The saturation magnetization and coercivity for Ni-MWNTs are 1.0 emu/gm and 230 Oe. The temperature dependence of magnetization indicates superparamagnetic which is supported by the field-cooled and zero-field-cooled plots determining a blocking temperature ~ 300 K. These altered magnetic properties of Ni-MWNTs are mainly due to the contribution from carbon nanotube encapsulation. Both the shape and environment enhance the total magnetic anisotropy of encapsulated nanowires at least by a factor of four. The encapsulation of metal nanowires in MWNTs tunes the magnetic properties of the system widely, e.g. from diamagnetic (pristine MWNTs) to paramagnetic (Ni-MWNT) to ferromagnetic (NiFe-MWNT) and a combination of para and ferro (NiFeCo-MWNT). Chapter 6: The conclusions of the different works presented in the thesis are coherently summarized in this chapter. Thoughts for future directions are also summed up. Appendix A: Spin dynamics in conducting polymer PEDOT-PSS in its pristine, processed with DMSO and nanocomposite form (with carbon nanotubes) is studied using solid state nuclear magnetic resonance (NMR). Plots of proton spin lattice relaxation times vs. temperature at a fixed frequency 23.4 MHz are compared to study the effect of the external agents on the polymer dynamics.

One interesting approach is the development of conductive polymer composite fibers for innovative textile applications such as in sensors, actuators and electrostatic discharge. In this study, conductive polymer composite fibers were prepared using several different blends containing conductive components: a conjugated polymer (polyaniline-complex) and/or carbon nanotubes. Different factors such as processing parameters, the morphology of the initial blends and the final fibers, fiber draw ratio and material selection were studied separately to characterize their effects on the fiber properties. In binary blends of PP/polyaniline-complex, the processing conditions, the matrix viscosity and the fiber draw ratio had substantial effects on the electrical conductivity of the fibers and linearity of resistance-voltage dependence. These factors were associated with each other to create conductive pathways through maintaining an appropriate balance of fibril formation and breakage along the fiber. The blend morphology was defined as the initial size of the dispersed conductive phase (polyaniline-phase), which depended on the melt blending conditions as well as the PP matrix viscosity. Depending on the initial droplet phase size, an optimum draw ratio was necessary to obtain maximum conductivity by promoting fibril formation (sufficient stress) and preventing fibril breakage (no excess stress) to create continuous pathways of conductive phase. Ternary blend fibers of PP/PA6/polyaniline-complex illustrated at least three-phase morphology with matrix/core-shell dispersed phase style. When ternary fibers were compared to binary fibers, the former could combine better mechanical and electrical properties only at a specific draw ratio; this showed that draw ratio was a more determinant factor for the ternary fibers, as both conductivity and tensile strength depended on the formation of fibrils from the core-shell droplets of the PA6/polyaniline-complex through the polypropylene matrix. The achieved maximum conductivity so far was in the range of 10 S/cm to 10 S/cm, which for different samples were observed at different fiber draw ratios depending on the mixing conditions, the matrix viscosity or whether the fiber was a binary or ternary blend. To improve the properties, PP/polyaniline-complex blends were filled with CNTs. The CNTs and the polyaniline-complex both had an increasing effect on the crystallization temperature and the thermal stability of PP. Furthermore, the maximum conductivity was observed in samples containing both CNTs and polyaniline-complex rather than the PP with either one of the fillers. Although increasing the content of CNTs improved the conductivity in PP/CNT fibers, the ease of melt spinning, diameter uniformity and mechanical properties of fibers were adversely affected. Diameter variation of PP/CNT as-spun fibers was shown to be an indication of hidden melt-drawings that had occurred during the fiber extrusion; this could lead to variations in morphology such as increases in the insulating microcracks and the distance between the conductive agglomerates in the drawn parts of the fiber. Variations in morphology result in variations in the electrical conductivity; consequently, the conductivity of such inhomogeneous fiber is no longer its physical property, as this varies with varying size. / Thesis to be defended in public on Friday, May 20, 2011 at 10.00 at KC-salen, Kemigården 4, Göteborg, for the degree of Doctor of Philosophy.

Carbon nanotubes have been envisioned to become a very important material in various applications. This is due to the unique properties of carbon nanotubes which can be exploited in applications on length scales spanning from the nano world to our macroscopic world. For example, the electronic properties of carbon nanotubes makes them utterly suitable for nano electronics while the strength of them makes them suitable for reinforcements in plastics. Both of these applications do however require... mer the ability for systematic production of carbon nanotubes with certain properties. This is called selective carbon nanotube growth and today this has not been achieved with total success. In the work presented in the thesis several different computational methods have been applied in our contribution to the systematic search for selective carbon nanotube growth. Put in a context of previous knowledge about carbon nanotube growth our results provide valuable clues to which parameters that control the carbon nanotube growth. In association with the latest results we even dare to, with all modesty, speculate about a plausible control mechanism. The studies presented in the thesis addressed different stages of carbon nanotube growth, spanning from the properties affecting the initiation of the growth to the parameters affecting the termination of the growth. In some more detail this included studies of the melting temperatures of nanoscaled metal clusters. The expected size dependence of the melting temperatures was confirmed and the melting temperatures of clusters on substrates were seen to depend both on the material and shape of the surface. As this constitute the premises prior to the carbon nanotube growth it was followed by studies of the interaction between carbon nanotubes and metal clusters of different size and constitution. This was done using different computational methods and at different temperatures. It soon became apparent that the clusters adapted to the carbon nanotube and not vice versa. This held true irrespectively of the constitution of the cluster, that is for both pure metal and metal carbide. It was also seen that there exist a minimum cluster size that prevent the carbon nanotube end from closing. Closure of the carbon nanotube end is likely to lead to the termination of the growth which lead to studies of other reasons for growth termination, e.g., Ostwald ripening of the catalyst particles. This was investigated with the result that the rate of the Ostwald ripening may depend on both the chirality and diameter of the carbon nanotubes. It is suggested that this may provide some answers to the controlled growth of carbon nanotubes. / <p>Disputationen sker fredagen den 3 december 2010, kl. 10:15, Kollektorn, Kemivägen 9</p>

Ce travail expérimental porte sur l'influence des paramètres de synthèse de nanotubes de carbone par CVD sur leurs caractéristiques structurales. Cette étude repose sur des analyses ex situ et in situ par spectroscopie Raman d'échantillons synthétisés sous diverses conditions de croissance. Une étude sur des films de cobalt oxydés a montré qu'il existe une variation de la pression seuil pour la croissance de nanotubes de carbone en fonction de l'épaisseur de cobalt que nous proposons d'attribuer à une pression seuil de réduction des particules.Une étude des bandes D et G' nous a permis d'attribuer les composantes basses fréquences aux nanotubes mono-feuillets et les composantes hautes fréquences à des espèces carbonées co-produites lors de la synthèse. Cette nouvelle approche a permis une étude plus fine des défauts et la proposition d'un modèle de création des défauts dans les nanotubes synthétisés par CVD. Enfin, une étude systématique des RBM nous a permis de mettre en évidence des processus favorisant la croissance de nanotubes mono-feuillets de petits ou de moyens diamètres. Ainsi, le contrôle de l'épaisseur de catalyseur, de la nature du précurseur carboné, de sa pression partielle ou encore de la température de synthèse permet de contrôler la distribution en diamètre des nanotubes mono-feuillets. / This experimental work deals with the influence of CVD growth parameters on carbon nanotube structural properties. The study is based on in situ and ex situ Raman spectroscopy on samples synthesized under various conditions of growth. A work on oxidized cobalt films showed that the threshold pressure for nanotube growth depends on the thickness of the cobalt film. We assign this pressure to a threshold pressure of reduction. A study of the D-band and G'-band allowed to assign low-frequency components to SWNT and high-frequency components to carbonaceous co-products of synthesis. This new approach allowed a fine study of defects which led to a model for defect creation in SWNT grown by CVD. A systematic study of RBM showed the processes leading to the preferential growth of small- or medium-diameter SWNT. Thus, control of catalyst thickness, of carbonaceous precursor nature and partial pressure or of synthesis temperature allows to control the diameter distribution of SWNT.

Dans ce travail, nous exposons une méthode basée sur la détection localisée en couplage capacitif de la composante électrique du signal RMN via des micro/nano sondes spécifiquement développées. Dans la première étape de ce travail nous avons utilisé des NEMS à base de nanotube de carbone pour réaliser une détection du signal RMN à l'échelle nanométrique. En effet, grâce à un couplage électromécanique, nous avons caractérisé ces systèmes en émission de champ, déterminé expérimentalement leur fréquence de résonance et montré qu'ils sont capables de détecter un signal radiofréquence. Pour utiliser ces dispositifs en RMN, l'adaptation du champ statique B0 de l'aimant pour atteindre la valeur de la fréquence de Larmor d'un atome est nécessaire. L'excitation locale autour de ces systèmes permettra une caractérisation complète et fiable. Pour mettre en place cette excitation localisée, nous avons choisi, dans la deuxième étape de cette thèse, une sonde locale de champ électromagnétique à l'échelle micrométrique. D'abord, nous présentons des simulations autour de la microsonde, décrivant la propagation des champs électrique et magnétique injectée par la microsonde. Nous avons caractérisé la microsonde en mode collection. Nous montrons une décroissance de l'intensité du signal RMN, en fonction de la distance. Nous avons observé et modélisé démontrant ainsi que La microsonde est capable de détecter localement un signal RMN tandis que la bobine capte de façon globale. Nous présentons les premières expériences de l'utilisation de la microsonde en mode émission. Ces mesures nous fournissent un modèle qui décrit une excitation inhomogène, dûe à l'émission locale de la puissance (décroissance exponentielle de la puissance), proche de la microsonde. Une distribution des angles de basculement est répartie d'une façon inhomogène induisant une distribution des intensités du signal RMN autour de la microsonde. À la fin de cette thèse, nous avons réalisé deux expériences comme applications directes suite des études sur la caractérisation de la microsonde. La première consiste à imager un volume d'eau placé dans un bain d'huile de silicone. L'image est obtenue en déplaçant mécaniquement la microsonde et en réalisant pour chaque point une mesure de spectroscopie localisée. Dans la deuxième expérience, la microsonde est utilisée pour injecter dans ce volume d'eau des impulsions électromagnétiques et détecte à la suite le signal RMN. Notre étude sur la caractérisation de l'émission locale par une microsonde et la détection du signal radiofréquence par un NEMS à base de NTC, nous permet de proposer un nouveau type de dispositifs capable de détecter un signal RMN. / In this work, we explain our method based on the detection localized capacitive coupling of the electric component of the NMR signal via micro/nano probes specifically developeds. In the first stage of this work we use NEMS based on carbon nanotube to achieve a detection of the NMR signal at the nanoscale. Because of an electromechanical coupling, we characterize these systems in field emission, and we determine experimentally their resonance frequency and shown that they are able to detect a radio signal. To use these devices in NMR, it is necessary to adapt the value of the static field B0 of the magnet to reach the value of the Larmor frequency. We found that a local excitement around these systems gives them a reliable characterization, to avoid disrupting the parasite measurements. To implement this localized excitation, we choose a micro-probe (coaxial cable). First, we presente simulations, describing the propagation of electric and magnetic fields transmitted by the microprobe. After we characterize in collection mode the microprobe. This study shows us a decrease of the NMR signal as a function as distance. This proves that the microprobe is able to detect an NMR signal in near field, while the coil picks up globally. We characterize the microprobe in the transmit mode . These measurements provide us with a model that describes an inhomogeneous excitation of nuclei, due to the emission of power in vicinity of the microprobe. An inhomogeneous distribution of tilt angles induces an inhomogeneous distribution of the NMR signal around the microprobe. At the end of this thesis, we conducte two applications such as direct studies on the characterization of the microprobe. The first consist to image a small volume of water placed in silicone oil sample. The image obtained by mechanically moving of the microprobe and making a localized spectroscopy. In the second experiment, the microprobe injected into this volume and detects after the NMR signal. Finally, the characterization in transmit mode of the microprobe allows us to better understand the phenomenon of the trasmission of electromagnetic waves to excite the spins of the nuclei in vicinity of the NEMS based on CNT. The latter being used as NMR probe at the nanoscale, to detect a NMR signal.

The mixing of polymers and nanoparticles makes it possible to give advantageous macroscopic material performance by tailoring the microstructure of composites. In this thesis, five combinations of nano inclusion and polymer matrix have been investigated. The first type of composites is titanium dioxide/ polyaniline combination. The effects of 4 different doping-acids on the microstructure, morphology, thermal stability and thermoelectric properties were discussed, showing that the sample with HCl and sulfosalicylic dual acids gave a better thermoelectric property. The second combination is titanium dioxide/polystyrene composite. Avrami equation was used to investigate the crystallization process. The best fit of the mass derivative dependence on temperature has been obtained using the double Gaussian dependence. The third combination is titanium dioxide/polyaniline/ polystyrene. In the titanium dioxide/polyaniline/ polystyrene ternary system, polystyrene provides the mechanical strength supporting the whole structure; TiO2 nanoparticles are the thermoelectric component; Polyaniline (PANI) gives the additional boost to the electrical conductivity. We also did some investigations on Polyethylene odide-TiO2 composite. The cubic anatase TiO2 with an average size of 13nm was mixed with Polyethylene-oxide using Nano Debee equipment from BEE international; Single wall carbon nanotubes were introduced into the vinyl acetate-ethylene copolymer (VAE) to form a connecting network, using high pressure homogenizer (HPH). The processing time has been reduced to 1/60 of sonication for HPH to give better sample quality. Theoretical percolation was derived according to the excluded volume theory in the expression of the threshold as a function of aspect ratio.

Este trabalho foi dividido em quatro etapas, além da introdução. A primeira parte consiste no estudo comparativo do comportamento eletroquímico de eletrodos de cobre em soluções tampão fosfato 0,10 mol L-1 com valores de pH 4,5 e 7,8, e em solução de NaOH com valores de pH 13,0 e 14,0. Mostrou-se que as espécies formadas eletroquimicamente sobre a superfície do eletrodo são dependentes do valor de pH e do potencial aplicado. Os resultados experimentais obtidos estão de acordo com aqueles reportados na literatura. A segunda parte da tese corresponde ao desenvolvimento de um sensor eletroquímico fabricado com microeletrodos de cobre para a determinação de peróxido de hidrogênio (H2O2) em amostras comerciais de antissépticos bucais e clareadores dentais. Nas condições experimentais otimizadas (solução tampão fosfato 0,10 mol L-1 (pH 7,0) e potencial de redução de -0,20 V), microeletrodos de cobre foram utilizados para a determinação de H2O2 sem a necessidade de etapas de extração, obtendo-se faixa linear de 0,015 a 6,4 mmol L-1 e limite de detecção de 2,8 &#181;mol L-1. O método proposto mostrou-se reprodutível e a presença de interferentes na matriz da amostra analisada não alterou a resposta do sensor para H2O2. Na terceira parte, a reação de eletro-oxidação de glicerol em superfícies de cobre em soluções de NaOH foi investigada utilizando a microscopia eletroquímica de varredura (SECM) no modo de geração pelo substrato de cobre / coleta no microeletrodo de platina (tip) (SG/TC). Os experimentos com a SECM mostraram a dependência da corrente com a distância entre o gerador e a tip, assim como a dependência com a concentração da solução de NaOH. Além disso, a corrente monitorada no microeletrodo diminuiu significativamente após a adição de glicerol. A atividade eletrocatalítica de eletrodos de cobre, no que diz respeito à oxidação de glicerol em meio alcalino, permitiu o desenvolvimento de um sensor amperométrico para a determinação de glicerol em amostra de biodiesel, com um intervalo linear de 0,05 a 1,33 mmol L-1 e limite de detecção de 20 &#181;mol L-1. A metodologia proposta foi aplicada para a determinação do analito em uma amostra de biodiesel de mamona. A quarta parte descreve a síntese, caracterização eletroquímica e utilização de nanotubos de carbono de paredes múltiplas (NCPM) decorados com nanopartículas de paládio (Pd) para a modificação da superfície de eletrodo de carbono vítreo (CV) para a oxidação de metanol, etanol e glicerol em solução de KOH 1,0 mol L-1. Os resultados mostraram que o NCPM/Pd é um bom catalisador para a eletro-oxidação de álcoois em meio alcalino e que maior atividade eletrocatalítica foi obtida para o glicerol. Em condições otimizadas, experimentos amperométricos foram realizados para o desenvolvimento do método analítico para a determinação de glicerol em biodiesel, obtendo-se um intervalo linear de 0,06 a 24 mmol L-1 e limite de detecção 30 &#181;mol L-1. Amostras de biodiesel foram analisadas com sucesso por meio de curvas de adição de padrão utilizando o eletrodo CV/NCPM/Pd. / This thesis is divided into four parts, apart from a general introduction. Part 1 is concerned with a critical comparison of the electrochemical behaviour of copper electrodes, in 0.10 mol L-1 phosphate buffer solution (pH 4.5 and 7.8), and in NaOH solution (pH 13.0 and 14.0). The electrochemical study showed that the species formed on the surface depends on both pH and the applied potential. The experimental results are in good agreement with those reported in the literature. A second goal of the thesis was the development of an electrochemical sensor for hydrogen peroxide (H2O2) determination in commercial oral antiseptic and dental whitening samples using copper microelectrodes. With optimized experimental conditions (working potential applied = -0.20 V in 0.10 mol L-1 phosphate buffer solution pH= 7.0), copper microelectrodes can be used to detect H2O2 without any previous extraction steps, in the range of 0.015 to 6.4 mmol L-1 with a lower detection limit of 2.8 &#181;mol L-1. In addition, the electrode exhibited an excellent reproducibility and long-term stability as well as negligible interference from sorbitol, ethanol, glycerin and saccharin. In the third part, the electrooxidation reaction of glycerol at copper surfaces in NaOH solutions was investigated using Scanning Electrochemical Microscopy (SECM) in a copper substrate generation / platinum microelectrode (tip) collection mode (SG/TC). The results showed the dependence of the current measured at the tip with respect to the distance between generator and the tip, as well as on the concentration of the NaOH solution. Other studies led to the conclusion that the current measured at the tip decreased significantly after addition of glycerol in the solution. The electrocatalytic activity of copper electrodes for the oxidation of glycerol in alkaline medium allowed the development of an amperometric method to determine glycerol in biodiesel samples in the range 0.05 to 1.33 mmol L-1 with a detection limit of 20 &#181;mol L-1. The determination of the analyte in a castor biodiesel sample employing a single copper microelectrode was carried out. The four part of this thesis shows results on the synthesis, electrochemical characterization and use of a glassy carbon (GC) electrode modified with multi-wall carbon nanotubes (MWCNT) decorated with palladium (Pd) for the electrochemical oxidation of methanol, ethanol and glycerol in 1.0 mol L-1 KOH solution. The results showed that MWCNT/Pd is a good electrocatalyst for methanol, ethanol and glycerol oxidation in alkaline medium, with highest activity toward glycerol oxidation. With optimized experimental conditions, an amperometric method was developed for the determination of glycerol in biodiesel samples, in the range of 0.06 to 24 mmol L-1 and detection limit of 30 &#181;mol L-1. Biodiesel samples were successfully analyzed by the standard addition method using the GC/MWCNT/Pd film electrode.

"Circulating tumor cells (CTCs) are cells released into the bloodstream from primary tumors and are suspected to be one of the main causes behind metastatic spreading of cancer. The ability to capture and analyze circulating tumor cells in clinical samples is of great interest in prevailing patient prognosis and clinical management of cancer. Carbon nanotubes, individual rolled-up graphene sheets, have emerged as exciting materials for probing the biomolecular interactions. With diameter of about 1 nm, they can attach themselves to cell surface receptors through specific antibodies and hold a great potential for diagnostic cellular profiling. Carbon nanotubes can be either semiconducting or metallic, and the electronic properties of either type rivals the best known materials. Small size of nanotubes and the ability to functionalize their surface using 1-Pyrenebutanoic Acid, Succinimidyl Ester (PASE), enables a versatile probe for developing a platform for capture and analysis of cancer biomarkers and circulating tumor cells. Although nanotubes have previously been used to electrically detect a variety of molecules and proteins, here for the first time we demonstrate the label free capture of spiked breast cancer cells using ultra-thin carbon nanotube film micro-array devices in a drop of buffy coat and blood. A new statistical approach of using Dynamic Time Warping (DTW) was used to classify the electrical signatures with 90% sensitivity and 90% specificity in blood. These results suggest such label free devices could potentially be useful for clinical capture and further analysis of circulating tumor cells. This thesis will go in-depth the properties of carbon nanotubes, device fabrication and characterization methodologies, functionalization protocols, and experiments in buffy coats and in blood. Combination of nano and biological materials, functionalization protocols and advanced statistical classifiers can potentially enable clinical translation of such devices in the future. "