Neste trabalho foram produzidos compósitos de nanotubos de carbono contendo nanopartículas de prata, os quais foram testados como substratos SERS (Surface-enhanced Raman Spectroscopy) na detecção do cristal violeta. Para obter tais compósitos foram necessárias modificações de nanotubos de carbono através de funcionalizações químicas para inserção de grupos carboxila e tiol, capazes de interferir no crescimento de nanopartículas metálicas através de um processo de redução térmica do acetato de prata sobre a superfície das amostras de nanotubo. Para a preparação de tais compósitos foram utilizadas duas amostras de nanotubos, uma de parede simples (SWNT) e outra de paredes múltiplas (MWNT) a fim de avaliar diferenças nos tamanhos e homogeneidade das nanopartículas formadas. Utilizou-se como ferramenta investigativa a espectroscopia Raman na caracterização destes compósitos, que forneceu informações sobre interação dos nanotubos de carbono com as nanopartículas de prata e mudanças estruturais ocasionadas durante a gama de funcionalizações. Para avaliar a morfologia dos compósitos foi utilizada a microscopia eletrônica de varredura (MEV) e a microscopia eletrônica de transmissão (TEM) que forneceram informações sobre o tamanho e a disposição das nanopartículas formadas através do tratamento térmico dos nanotubos com acetato de prata. Os compósitos preparados foram aplicados como substrato SERS na detecção do cristal violeta. Nesta aplicação foi avaliada a capacidade dos nanotubos em adsorver estas moléculas e o potencial do substrato na intensificação do espectro Raman do analito. Observou-se que a adsorção do cristal violeta sobre uma amostra de SWNT foi máxima após o tempo de 60 minutos de agitação. Já o substrato utilizado (SWNT-COOH@Ag) permitiu a detecção do cristal violeta em solução aquosa com concentração de até 1,0.10-8 mol.L-1. Utilizando o mapeamento Raman foi possível avaliar a presença do analito através do monitoramento de uma banda do espectro vibracional do analito intensificada pelo efeito SERS / In this work, we produced carbon nanotube composites containing silver nanoparticles, which were tested as SERS (Surface-enhanced Raman Spectroscopy) substrates in the detection of crystal violet. For these the synthesis of these composites modifications of the carbon nanotubes surface through chemical functionalizations were necessary for insertion of carboxyl and thiol groups, that can affect the growth of metal nanoparticles in thermal reduction process of silver acetate on the surface of the nanotube samples. For the preparation of such composites have single walled carbon nanotubes (SWNT) and a multi-walled carbon nanotubes (MWNT) to evaluate differences in size and homogeneity of the nanoparticles formed. Raman spectroscopy was used as an investigative tool in the characterization of these composites, which provided information on the interaction of carbon nanotubes with silver nanoparticles and structural changes ocurring during the range of functionalizations. To evaluate the morphology of the composites scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used. These techniques provided information about the size and assembly of the silver nanoparticles formed by heat treatment of the nanotubes with silver acetate. The nanotubes@Ag composites were applied as SERS substrates in the detection of crystal violet. In this application, we evaluated the ability of nanotubes to adsorb these molecules and the substrate potential in enhancing the Raman spectrum of the analyte. It was observed that the adsorption of the crystal violet on a sample of SWNT was maximal after 60 minutes of stirring. Substrate used (SWNT-COOH @ Ag) allowed detection of crystal violet in aqueous solution with a concentration as low as 1,0.10-8 mol.L-1. Using Raman mapping was possible to evaluate the presence of the analyte by monitoring a band of vibrational spectrum of the analyte enhanced by SERS effect.

Single Wall Carbon Nanotubes (SWNTs), discovered in 1993, have good mechanical, electrical and thermal properties. Polyacrylonitrile (PAN) is an important fiber for textiles as well as a precursor for carbon fibers. PAN has been produced since 1930s. In this study, we have processed SWNT/PAN fibers by dry-jet wet spinning. Purified SWNT, nitric acid treated SWNTs, and benzonitrile functionalized SWNTs have been used. Fiber processing was done in Dimethyl Formamide (DMF) and coagulation was done in DMF/water mixture. The coagulated fibers were drawn (draw ratio of 6) at 95 oC. Structure, orientation, and mechanical properties of these fibers have been studied. The cross-sections for all the fibers are not circular. Incorporation of SWNT in PAN results in improved mechanical properties, tensile modulus increased from 7.9 GPa for control PAN to 13.7 GPa for SWNT/PAN composite fiber, and functionalized SWNTs result in higher improvements with tensile modulus reaching 17.8 GPa for acid treated SWNT/PAN composite fibers. The theoretical analysis suggests that observed moduli of the composite fibers are consistent with the predicted values.

Carbon nanotubes are appealing materials for nanofabrication due to their unique properties and structures. However, for carbon nanotubes to be used in mass-fabricated devices, precise control of nanotube orientation and location on surfaces is critical. I have developed a technique to align single-walled carbon nanotubes (SWNTs) on surfaces from a droplet of nanotube suspension under gas flow. Fluid motion studies indicate that alignment is likely due to circulation of SWNTs in the droplet. My work provides a facile method for generating oriented nanotubes for nanodevice applications. I have also devised an approach for localizing SWNTs onto 1-pyrenemethylamine-decorated DNA on surfaces. I found that 63% of SWNTs on surfaces were anchored along DNA, and these nanotubes covered ~5% of the total DNA length. This technique was an initial demonstration of DNA-templated SWNT localization. In an improved method to localize SWNTs on DNA templates, dodecyltrimethylammonium bromide was utilized to suspend SWNTs in aqueous media and localize them on DNA electrostatically. SWNT positioning was controlled by the surface DNA arrangement, and the extent of deposition was influenced by the SWNT concentration and number of treatments. Under optimized conditions, 83% of the length of surface DNAs was covered with SWNTs, and 76% of the deposited SWNTs were on DNA. In some regions, nearly continuous SWNT assemblies were formed. This approach should be useful for the fabrication of nanotube nanowires in nanoelectronic circuits. Using my improved procedures, I have localized SWNTs on DNA templates across electrodes and measured the electrical properties of DNA-templated SWNT assemblies. When a DNA-templated SWNT was deposited on top of and bridging electrodes, the measured conductance was comparable to literature values. In contrast, SWNTs with end-on contacts to the sides of electrodes had conductances hundreds of times lower than literature values, probably due to gaps between the SWNT ends and the electrodes. This work provides a novel approach for localizing SWNTs across contacts in a controlled manner. These results may be useful in the fabrication of nanoelectronic devices such as transistors with SWNTs as active components. Moreover, this approach could be valuable in arranging SWNTs as electrical interconnects for nanoelectronics applications.

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La spintronique moléculaire et la photocatalyse sont deux domaines en constante évolution. Le premier s’attache à exploiter la possibilité de coupler deux phénomènes physiques, à savoir le transport d’un flux de porteurs de charges et le spin de l’électron, tandis que le second se concentre sur l’exaltation des propriétés chimiques de transfert d’électrons d’une espèce donnée grâce au phénomène physique d’irradiation lumineuse. Depuis quelques années, les nanotubes de carbone ont suscité un grand intérêt à la fois en tant que composant pour la spintronique moléculaire, en raison de leur grande cohérence de spin, et en tant que support idéal pour la catalyse moléculaire, grâce à leurs exceptionnelles propriétés électroniques de surface. Au cours de ce travail de thèse, nous nous sommes attachés à concevoir des complexes inorganiques possédant des propriétés physiques, (magnétiques ou optiques) et des propriétés chimiques (permettant leur assemblage non-covalent sur des nanotubes de carbone monoparoi) de manière à former des adduits complexes inorganiques-nanotubes aux propriétés exploitables en spintronique moléculaire et en photocatalyse. Les propriétés des complexes synthétisés ont été extensivement caractérisées (Chapitre 2), et les plus prometteurs de ces composés ont été assemblés avec succès sur les nanotubes de carbone (Chapitre 3), comme en attestent les mesures spectroscopiques réalisées. Enfin, les deux domaines d’applications concernés par nos travaux faisant intervenir des phénomènes de transport électronique, des études spécifiques sur des dispositifs électriques de type transistor à effet de champ dont le canal de conduction est constitué de nanotubes de carbone ont été réalisées (Chapitre 4). Celles-ci mettent à chaque fois en évidence l’existence d’une communication électronique entre les complexes inorganique et les nanotubes de carbone sur lesquels ils sont assemblés au sein des dispositifs. Bien qu’au final un couplage entre les propriétés magnétiques des complexes synthétisés et les propriétés de transport des nanotubes n’ait pas pu être mis en évidence, de nombreux phénomènes inattendus et extrêmement intéressants tels que des effets ambipolaires, des transferts de charge ou des ruptures de liaisons ont été observés. Par contre, un fort couplage opto-électronique a pu être obtenu entre un complexe et le flux de porteurs de charge des dispositifs, ce qui s’avère être de très bon augure pour des futures applications en photocatalyse. / Molecular spintronic and photocatalysis are two fields in constant evolution. While the first deals with the coupling of two physical properties, the flux of charge carriers and the spin of the electron, the second is focusing on the enhancement of the electron transfer of chemical species under light irradiation. Recently, there has been an increasing interest in carbon nanotubes as new components for molecular spintronics, since they possess high spin coherence, and as ideal materials for molecular catalysis, for their tremendous electronic surface properties. Our work consisted in conceiving inorganic complexes with both physical (magnetic or optic) and chemical (ability of realizing non covalent assembly on single-walled carbon nanotubes) properties, in order to create new nanotube-complex nanohybrids which could be exploited for molecular spintronics or photocatalysis applications. The properties of the synthesized complexes were extensively characterized (Chapter 2), and the most promising molecules were successfully assembled onto carbon nanotubes, as is proven by the spectroscopic measurement which were performed (Chapter 3). Finally, since both domains of applications we considered involve electronic transportation, specific studies were realized on field effect transistor devices with carbon nanotubes as the conduction channel (Chapter 4). They evidence strong electronic communications between the inorganic complexes and the carbon nanotubes onto which they are assembled in the devices. Even if in the end no coupling was observed between the magnetic properties of the inorganic complexes and the transport ones of the carbon nanotubes, numerous unexpected and very interesting phenomena such as ambipolar behavior, charge transfer effect or bond cleavage were evidenced. As for the optoelectronic coupling which was investigated for photocatalytic applications, a first step was made as the transport of the carbon nanotube field effect transistor devices onto which a complex was assembled shows a strong dependence with the applied light irradiation.

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.

Carbon nanotubes show a wide range of transport behavior that varies from ballistic to hopping regime, depending on the nature of disorder in the system. Minute variations in disorder can lead from weak to strong localization, and this yields complex and intriguing features in the analysis of transport data. This dissertation reports an experimental study of charge transport in optically transparent single-wall carbon nanotube (SWNT) networks and field-effect devices. The SWNT network comprises randomly aligned (bundles of) tubes that have both high optical transparency in visible, near-infrared (IR) wavelength range and high electrical conductivity. Various aspects of charge transport in this material including magnetotransport, high electric-field transport and gate induced field-effect are investigated and presented within a consistent framework. The temperature dependence of resistance suggests hopping transport in the network. Since strong localization is observed for the disordered network, the disorder is further characterized by a magnetotransport study and a pulsed electric-field dependence study down to low temperatures (1.3 K). The magnetoresistance (MR) has contributions from two quantum effects -a forward interference mechanism leading to a negative MR and a wavefunction shrinkage mechanism leading to positive MR. The temperature dependence of the coefficient of this negative MR is shown to follow inverse power-law dependence, in accordance with theoretical predictions. The intrinsic parameters obtained from this analysis suggest a transverse localization of charge on the bundle boundaries. The electric-field dependence, measured to high fields, follows the predictions of hopping transport in high electric-field regime. A scaling analysis indicates that electric-field and temperature play similar roles in the transport. The calculated dependence of ‘threshold electric-field’ is also suggestive of this competing process between phonons and electric-field. The applicability of the concept of ‘effective temperature’ is explored for this system; the electric-field induced suppression of MR is studied. The network resistance as well as the optical transparency of the network is modulated with gate voltage using an electrolyte gate dielectric. The gating can tune the absorptions associated with the van Hove singularities in the SWNT DOS and a time response study for this ‘smart window’ is done for the modulation. A novel technique is used to characterize organic and nanotube field-effect transistors and this allows estimation of device parameters such as transconductance and channel impedance. The ac impedance of the SWNT network is also investigated as a possible tool to probe network connectivity. To summarize, the role of disorder in charge transport is investigated for these novel transparent SWNT networks using magnetic-field, electric-field, temperature and field-effect dependent transport measurements.

La spintronique moléculaire et la photocatalyse sont deux domaines en constante évolution. Le premier s'attache à exploiter la possibilité de coupler deux phénomènes physiques, à savoir le transport d'un flux de porteurs de charges et le spin de l'électron, tandis que le second se concentre sur l'exaltation des propriétés chimiques de transfert d'électrons d'une espèce donnée grâce au phénomène physique d'irradiation lumineuse. Depuis quelques années, les nanotubes de carbone ont suscité un grand intérêt à la fois en tant que composant pour la spintronique moléculaire, en raison de leur grande cohérence de spin, et en tant que support idéal pour la catalyse moléculaire, grâce à leurs exceptionnelles propriétés électroniques de surface. Au cours de ce travail de thèse, nous nous sommes attachés à concevoir des complexes inorganiques possédant des propriétés physiques, (magnétiques ou optiques) et des propriétés chimiques (permettant leur assemblage non-covalent sur des nanotubes de carbone monoparoi) de manière à former des adduits complexes inorganiques-nanotubes aux propriétés exploitables en spintronique moléculaire et en photocatalyse. Les propriétés des complexes synthétisés ont été extensivement caractérisées (Chapitre 2), et les plus prometteurs de ces composés ont été assemblés avec succès sur les nanotubes de carbone (Chapitre 3), comme en attestent les mesures spectroscopiques réalisées. Enfin, les deux domaines d'applications concernés par nos travaux faisant intervenir des phénomènes de transport électronique, des études spécifiques sur des dispositifs électriques de type transistor à effet de champ dont le canal de conduction est constitué de nanotubes de carbone ont été réalisées (Chapitre 4). Celles-ci mettent à chaque fois en évidence l'existence d'une communication électronique entre les complexes inorganique et les nanotubes de carbone sur lesquels ils sont assemblés au sein des dispositifs. Bien qu'au final un couplage entre les propriétés magnétiques des complexes synthétisés et les propriétés de transport des nanotubes n'ait pas pu être mis en évidence, de nombreux phénomènes inattendus et extrêmement intéressants tels que des effets ambipolaires, des transferts de charge ou des ruptures de liaisons ont été observés. Par contre, un fort couplage opto-électronique a pu être obtenu entre un complexe et le flux de porteurs de charge des dispositifs, ce qui s'avère être de très bon augure pour des futures applications en photocatalyse.

The graphitic nature, continuous structure, and high mechanical properties of carbon nanotubes (CNTs) make them good candidate for reinforcing polymer fiber. The different types of CNTs including single-wall carbon nanotubes (SWNTs), few-wall carbon nanotubes (FWNTs), and multi-wall carbon nanotubes (MWNTs), and carbon nanofibers (CNFs) differ in terms of their diameter and number of graphitic walls. The desire has been to increase the concentration of CNTs as much as possible to make next generation multi-functional materials. The work in this thesis is mainly focused on MWNT and CNF reinforced polyacrylonitrile (PAN) composite fibers, and SWNT, FWNT, and MWNT reinforced poly(etherketone) (PEK) composite fibers. To the best of our knowledge, this is the first study to report the spinning of 20% MWNT or 30% CNF reinforced polymer fiber spun using conventional fiber spinning. Also, this is the first study to report the PEK/CNT composite fibers. The fibers were characterized for their thermal, tensile, mechanical, and dynamic mechanical properties. The fiber structure and morphology was studied using WAXD and SEM. The effect of two-stage heat drawing, sonication time for CNF dispersion, fiber drying temperature, and molecular weight of PAN was also studied. Other challenges associated with processing high concentrations of solutions for making composite fibers have been identified and reported. The effect of CNT diameter and concentration on fiber spinnability and electrical conductivity of composite fiber have also been studied. This work suggests that CNT diameter controls the maximum possible concentration of CNTs in a composite fiber. The results show that by properly choosing the type of CNT, length of CNTs, dispersion of CNTs, fiber spinning method, fiber draw ratio, and type of polymer, one can get electrically conducting fibers with wide range of conductivities for different applications. The PEK based control and composite fibers possess high thermal stability with almost no weight loss up to 500 degree C and negligible thermal shrinkage up to 200 degree C. The PEK based fibers showed high toughness which surpassed many of the high-performance fibers like Kevlar(R) and Zylon(R). The 10% FWNT containing fiber is unique in terms of high electrical conductivity and high toughness. The CNT based fibers may be used as structural material, fire-barrier/protection textile, electrode for electrochemical capacitor or fuel cells, and as a template for directional growth of tissues.

Organic electronic devices are receiving growing interest because of their potential to employ lightweight, low-cost materials in a flexible architecture. Typically, indium tin oxide (ITO) is utilized as the transparent positive electrode in these devices due to its combination of high transmission in the visible spectrum and high electrical conductivity. However, ITO may ultimately hinder the full market integration of organic electronics due to its increasing cost, the limited availability of indium, lack of mechanical flexibility, and sustainability with regards to the environment and material utilization. Therefore, alternatives for ITO in organic electronics are currently being pursued. Transparent electrodes comprised of single wall carbon nanotubes (SWNTs) are an appealing choice as a surrogate because of the extraordinary electrical and mechanical properties these 1-D structures posses. As such, the research presented in this dissertation has been conducted to advance the goal of manufacturing SWNT networks with transparent electrode properties that meet or exceed those of ITO. To this end, SWNT films were characterized with regard to the collective and individual optoelectronic properties of the SWNTs that comprise the network. Specifically, corroborative theoretical and experimental observations were employed to expand the understanding of how the optoelectronic properties of polydisperse and monodisperse SWNT networks are enhanced and sustained through chemical treatment and subsequent processing. In addition, the impact of interfacial electrical contact resistance between SWNT electrodes and metallic fingers often used in photovoltaic system applications was elucidated. In summary, the research presented in this dissertation can be leveraged with present state of the art in SWNT films to facilitate future SWNT electrode development.