This research work focuses on single wall carbon nanotube (SWNT)/polymer composites and novel structured electrospun polymer materials. Poly (methyl methacrylate) (PMMA) is used as polymer matrix. Obtaining SWNT/PMMA composite with enhanced mechanical and electrical properties is one of the research goals. The first important step is to figure out a method for achieving uniform SWNT dispersion in PMMA. Eight different solvents were used to disperse SWNT in PMMA. It is found that the polar component of the solubility parameter (£_p) of the solvent affects SWNT dispersion in PMMA. SWNT dispersion in PMMA improves with increasing solvent Ôp value, and the most uniform dispersion is obtained in nitromethane, which is the most polar solvent employed in this study. SWNT/PMMA composite films at various SWNT concentrations were processed employing nitromethane as the solvent. Mechanical and electrical property enhancements are observed. Processing, structure, morphology, and properties of these composites are discussed. A comparison between reinforcement efficiency of SWNT, multiwall carbon nanotubes (MWNT), and vapor grown carbon nano fibers (VGCNF) in PMMA is also discussed. In order to electrospin SWNT/PMMA/nitromethane solution into composite nanofibers successfully, first PMMA was electrospun. With increasing solution concentration, morphology of the electrospun polymer changed from particles to fibers. At relatively low solution concentrations, micro- and nano-structured polymer particles, and at higher solution concentrations, porous and solid nanofibers are observed. SWNT/PMMA/nitromethane solution was electrospun into polymer shell-SWNT core nanofibers. Solvent characteristics play an important role on particle or fiber mat morphology. The qualitative relationship between solvent properties (evaporation rate, dielectric constant, surface tension, and viscosity) and particle morphologies is discussed. By tailoring solution properties and electrospinning conditions, one can produce particles or fibers with controlled morphology for specific applications.

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 235-246).

Le contexte scientifique de cette thèse s'inscrit dans le domaine de la bioélectronique et l'objectif vise la mise au point de dispositifs diamant pour des applications en chimie analytique, diagnostic clinique ou encore dans le domaine médical. Un des axes de travail est basé sur la mise au point d'une nouvelle technique de fonctionnalisation du diamant hydrogéné. Cette méthode est rapide, simple, mono-étape et ne nécessite pas d'apport extérieur d'énergie. La caractérisation du greffage par FTIR a permis de proposer un mécanisme réactionnel qui a été corroboré par l'étude de la cinétique réactionnelle. Nous avons mis en évidence que ce procédé permet l'obtention d'une liaison covalente stable carbone-carbone. Elle se révèle particulièrement adaptée à l'immobilisation directe d'espèces biologiques. En utilisant cette technique de greffage, il a été possible de concevoir des biopuces à ADN et protéines, ainsi qu'un biocapteur au peroxyde d'hydrogène de troisième génération. Enfin, le procédé étant basé sur la simple mise en contact de la solution de greffage avec le substrat, il est possible de structurer les dépôts à l'échelle nanométrique en faisant appel au Dip-Pen Nanolithography. En parallèle, un nouveau matériau composite diamant/nanotubes de carbone a été mis au point pour augmenter la surface développée des électrodes de diamant dopé au bore et en accroitre ainsi les performances. Dans ce cadre, une technique de gravure catalytique assistée par filament chaud a été utilisée pour enterrer des nanoparticules dans la couche diamant. Ces dernières assurent par la suite la croissance des nanotubes de carbone par dépôt chimique en phase vapeur. Cette méthodologie assure ainsi une meilleure adhérence des nanotubes sur leur substrat et permet de pallier aux problèmes de toxicité des nanotubes vis-à-vis des milieux biologiques. / The scientific context of this thesis is related to the field of bioelectronics. The objective is the development of diamond devices for applications in analytical chemistry, clinical diagnostic or medical devices. One of the axes deals with a new technique of functionalization of hydrogenated diamond surface. This method is fast, simple, one step and does not require contribution of exogenous energy. The characterization of the grafting by FTIR allowed us to suggest a mechanism which was confirmed by the study of the reaction kinetic. We brought to light that this process ensures the achievement of a stable covalent carbon-carbon bond. This methodology is particularly well adapted to the direct immobilization of biological species. By using this grafting technic, it was possible to design DNA and proteins biochips, as well as a hydrogen peroxide third generation biosensor. Finally, the process being based on the simple stake in contact of the grafting solution with the substrate, it is possible to structure functionalized areas at the nanometric scale using Dip-Pen Nanolithography. In parallel, a new composite diamond /carbon nanotubes material was developed to increase the specific surface of the boron doped diamond electrodes and so to increase its efficiency. In this frame, a new technic of catalytic etching assisted by hot filament was used to embed nanoparticles in the diamond layer. This process allowed afterward the growth of the carbon nanotubes by chemical vapor deposition. This methodology ensures markedly enhanced adhesion of the nanotubes on their substrate and obviates the problems of nanotubes toxicity towards their biological environment.

Dans le domaine du photovoltaïque, les cellules hybrides organiques sont une des voies les plus prometteuses, notamment grâce aux propriétés de collection de lumière des molécules de type chromophore. Les nanotubes de carbone, quant à eux, sont des nano-objets quasi unidimensionnels qui présentent des propriétés de transport exceptionnelles. La réalisation d’un couplage important entre une molécule collectrice de lumière et un nanotube de carbone représente donc une voie importante à explorer. Ce travail de recherche est consacré à l’étude du transfert d’énergie dans les composés nanotubes de carbone/chromophore. Une nouvelle méthode de fonctionnalisation non covalente des nanotubes de carbone est présentée. Basée sur une suspension micellaire de nanotubes, cette méthode permet d’obtenir un fort taux de fonctionnalisation tout en préservant les propriétés intrinsèques des nanotubes. Le transfert d’énergie est mis en évidence sur les composés nanotube/porphyrine par des mesures d’excitation de la photoluminescence sur ensemble de nanotubes ainsi que sur objets uniques. L’évaluation du rendement quantique de transfert par trois méthodes indépendantes montre un couplage de l’ordre de 100% entre la molécule et le nanotube- et ce malgré la faiblesse des interactions entre orbitales «Pi» mises en jeu dans la fonctionnalisation non covalente. Le dernier volet de ce travail est consacré à des mesures d’anisotropie à l’échelle de l’objet unique permettant d’obtenir des informations quant à l’arrangement des molécules à la surface des nanotubes. / In the field of photovoltaic, hybrid organic solar cells are one of the most promising ways, especially due to the light collection properties of chromophore molecules. On the other hand, carbon nanotubes are quasi one-dimensional nano-objects showing exceptional transport properties. The achievement of a significant coupling between a light harvesting molecule and a carbon nanotube is an important route to explore. This research is dedicated to the study of energy transfer in carbon nanotube/chromophore compounds. A new method of non-covalent functionalization of carbon nanotubes is presented. Based on a micellar suspension of nanotubes, this method provides a high degree of functionalization while preserving the intrinsic properties of nanotubes. The energy transfer is shown in nanotube/porphyrin compounds by photoluminescence excitation spectroscopy on ensembles as well as at the single molecule scale. The evaluation of the quantum efficiency of the transfer by three independent methods shows a coupling of the order of 100% between the molecule and the nanotube, despite the weak interactions between “Pi” orbitals involved in the non-covalent functionalization. The final part of this work is dedicated to anisotropy measurements on single compounds to gain information on molecular arrangement on the surface of nanotubes.

Cette thèse porte sur la catalyse supportée sur nanotubes de carbone. Plusieurs aspects ont été étudiés, électrocatalyse pour la production d'hydrogène à partir d'eau, catalyse pour la synthèse organique et électrocatalyse de la réaction de réduction de l'oxygène. Différents catalyseurs ont été synthétisés à partir d'assemblages supramoléculaires de molécules amphiphiles autour de nanotubes de carbone ou d'adhésion de molécules polyaromatiques à la surface des nanotubes et ont impliqué l'utilisation de catalyseur moléculaire ou nanoparticulaire. L'utilisation de ces catalyseurs pour les différents types de réactions mentionnés plus haut ont abouti à des résultats intéressants. / This PhD thesis deals with the catalysis supported on carbon nanotubes. Several aspects have been studied such as electrocatalysis for hydrogen production form water, catalysis for organic synthesis and electrocatalysis of the oxygen reduction reaction. Many different catalysts have been synthesized based on supramolecular assembly of amphiphilic molecules around carbon nanotubes or assembly of polyaromatic molecules at the surface of the nanotubes. These catalysts are made of metallic complexes or metallic nanoparticles. These catalysts have been successfully used to perform the reactions mentioned above.

My work presents a novel approach to fabricate binder free three-dimensional carbon nanotubes/sulfur (3DCNTs/S) hybrid composite by a facile and scalable method increasing the loading amount from 1.86 to 8.33 mg/cm2 highest reported to date with excellent electrochemical performance exhibiting maximum specific energy of ~1233Wh/kg and specific power of ~476W/kg, with respect to the mass of the cathode. Such an excellent performance is attributed to the fact that 3DCNTs offers higher loading amount of sulfur, and confine polysulfide within the structure. In second part of the thesis, molybdenum disulfide (MoS2) is typically studied for three electrochemical energy storage devices including supercapacitors, Li-ion batteries, and hybrid Li-ion capacitors. The intrinsic sheet like morphology of MoS2 provides high surface area for double layer charge storage and a layered structure for efficient intercalation of H+/ Li+ ions. My work demonstrates the electrochemical analysis of MoS2 grown on different substrates including copper (conducting), and carbon nanotubes. MoS2 film on copper was investigated as a supercapacitor electrode in three electrode system exhibiting excellent volumetric capacitance of ~330F/cm3 along with high volumetric power and energy density in the range of 40-80 W/cm3 and 1.6-2.4 mWh/cm3, respectively. Furthermore, we have developed novel binder-free 3DCNTs/ MoS2 as an anode materials in half cell Li-ion batteries. The vertically oriented morphology of MoS2 offers high surface area and active electrochemical sites for efficient intercalation of Li+ ions and demonstrating excellent electrochemical performance with high specific capacity and cycling stability. This 3DCNTs/ MoS2 anode was coupled with high surface area southern yellow pine derived activated carbon (SYAC) cathode to obtain hybrid 3DCNTs/ MoS2 || SYAC Li-ion capacitor (LIC), which delivers large operating voltage window of 1-4.0V with excellent cycling stability exhibiting capacitance retention of ~80% after 5000 cycles.

No description available.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

Composites of multi-walled carbon nanotubes (MWCNTs) with polypropylene (PP) and thermoplastic olefins (TPOs) were prepared by melt compounding. Two non-covalent functionalization methods were employed to improve nanotube dispersion and the resulting composite properties are reported. The first functionalization approach involved partial coating of the surface of the nanotubes with a hyperbranched polyethylene (HBPE). MWCNT functionalization with HBPE was only moderately successful in breaking up the large aggregates that formed upon melt mixing with PP. In spite of the formation of large aggregates, the samples were conductive above a percolation threshold of 7.3 wt%. MWCNT functionalization did not disrupt the electrical conductivity of the nanotubes. The composite strength was improved with addition of nanotubes, but ductility was severely compromised because of the existence of aggregates. The second method involved PP matrix functionalization with aromatic moieties capable of π-π interaction with MWCNT sidewalls. Various microscopy techniques revealed the addition of only 25 wt% of PP-g-pyridine (Py) to the neat PP was capable of drastically reducing nanotube aggregate size and amount. Raman spectroscopy confirmed improved polymer/nanotube interaction with the PP-g-Py matrix. Electrical percolation threshold was obtained at a MWCNT loading of approximately 1.2 wt%. Electrical conductivity on the order of 10-2 S/m was achieved, suggesting possible use in semi-conducting applications. Composite strength was improved upon addition of MWCNTs. The matrix functionalization with Py resulted in a significant improvement in composite ductility when filled with MWCNTs in comparison to its maleic anhydride (MA) counterpart. Preliminary investigations suggest that the use of alternating current (AC) electric fields may be effective in aligning nanotubes in PP to reduce the filler loading required for electrical percolation. Composites containing MWCNT within PP/ethylene-octene copolymer (EOC) blends were prepared. Microscopy revealed that MWCNTs localized preferentially in the EOC phase. This was explained by the tendency of the system to minimize interfacial energy when the MWCNTs reside in the thermodynamically preferential phase. A kinetic approach, which involved pre-mixing the MWCNTs with PP and adding the EOC phase subsequently was attempted to monitor the migration of MWCNTs. MWCNTs began to migrate after two minutes of melt mixing with the EOC. The PP-g-Py matrix functionalization appears to slightly delay the migration. A reduction in electrical percolation threshold to 0.5 wt% MWCNTs was achieved with a co-continuous blend morphology, consisting of a 50/50 by weight ratio of PP and EOC. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-09-30 13:22:24.499

Ce projet est consacré à la croissance de nanofils de SiC et de nanotubes de carbone par MPACVD dans un réacteur tubulaire. Les conditions de pré-traitement de la couche catalytique de fer, indispensable à la croissances des nanostructures, ont favorisé la croissance de l'une ou l'autre structure. Un pré-traitement agressif dans un plasma d'hydrogène a permit la croissance de nanofils constitués d'un coeur de ß-SiC et d'une gaine de carbone. L'originalité du procédé utilisé est que l'apport de silicium pour la croissance de ces nanofils provient du sustrat lui-même. Deuxièmement, une étude sur la nanostructuration d'une couche catalytique de fer a été réalisée. L'effet des paramètres plasma, l'épaisseur du catalyseur et le temps de pré-traitement sur la taille et la formation des particules a été montré. Un modèle explicatif a également été élaboré. Après la nanostructuration du catalyseur, une étude paramétrique sur la croissance de NTC a été entreprise. Nous avons montré l'effet des paramètres plasma, et du taux de gaz méthane utilisé sur la qualité et la structure des NTCs. Une corrélation entre l'épaisseur de la couche catalytique et le diamètre des NTCs a été établie. De plus pour un temps de pré-traitement relativement long la croissance de nanomurs de carbone a été favorisée. / We report in this study, the growth of silicon carbide nanofibers and carbon nanotubes by MPACVD. Regarding to the pre-treatment conditions of the catalytic layer, used in our reactor, one structure is promoted. An aggressive pre-treatment lead to the growth of a core-shell structure of SiC nanofibers. The core is constituted of ß-SiC and the shell of carbon. The originality of this process resides in the fact that the silicon source to grow these nanofibers is the substrate itself. Secondly, the control of the nanostructuration and the patterning of iron catalyst film was studied. The effect of the hydrogen plasma conditions on the diameter and the density of the catalyst nanoparticles was studied and discussed. We were then able to propose a comprehensive mechanism for the metallic nanostructuration. The growth of carbon nanotubes (CNTs) was than carried out on the patterned catalyst nanoparticles. The plasma parametric study revealed the effect of the plasma power and pressure as well as the methane gas ratio on the quality and structure of the produced CNTs. A corrolation of the catalyst thickness and the CNTs diameters has been demonstrated. High quality double-walled and multi-walled CNTs of a diameter of about 1 nm have than been obtained. Besides, we have noted the gowth of carbon nanowalls for relatively long pre-treatment times.