The focus of this study was to explore process-structure-property relationships in biodegradable polymer nanocomposite films in order to eliminate the commonly used trial and error approach to materials design and to enable manufacturing of composites with tailored properties for targeted applications. The nanofiller type and concentration, manufacturing method and compounding technique, as well as processing conditions were systematically altered in order to study the process-structure-property relationships. Polylactic acid (PLA) was used as the polymer and exfoliated graphite nanoplatelets (GNP), carbon nanotubes (CNT), and cellulose nanocrystals (CNC) were used as reinforcement. The nanocomposite films were fabricated using three different methods: 1) melt compounding and melt fiber spinning followed by compression molding, 2) solution mixing and solvent casting, and 3) solution mixing and electrospinning followed by compression molding. Furthermore, the physical properties of the polymer, namely the crystallization characteristics were altered by using two different cooling rates during compression molding. The electrical response of the composite films was examined using impedance spectroscopy and it was shown that by altering the physical properties of the insulating polymer matrix, increasing degree of crystallinity, the percolation threshold of the GNP/PLA films is significantly reduced. Additionally, design of experiments was used to examine the influence of nanofiller type (CNT versus GNP), nanofiller content, and processing conditions (cooling rate during compression molding) on the elastic modulus of the composite films and it was concluded that the cooling rate is the primary factor influencing the elastic modulus of both melt compounded CNT/PLA and GNP/PLA films. Furthermore, the effect of nanofiller geometry and compounding method was examined and it was shown that the high nanofiller aspect ratio in the CNT/PLA films led to decreased percolation threshold compared to the GNP/PLA films. The melt compounded GNP/PLA films displayed a lower percolation threshold than the solution cast GNP/PLA films most likely due to the more homogeneous distribution and dispersion of GNP in the solution cast films. Fully biodegradable and biorenewable nanocomposite films were fabricated and examined through the incorporation of CNC in PLA. Through the addition of CNC, the degree of crystallinity of the matrix was significantly increased. Focusing the design space through investigation of process-structure-property relationships in PLA nanocomposites, can help facilitate nanocomposites with tailored properties for targeted applications.

Graphene is a one-atom thick sheet of graphite which made of carbon atoms arranged in a hexagonal lattice. Carbon nanotubes and graphene nanoribbons can be viewed as single molecules in nanometer scale. Carbon nanotubes are usually labeled in terms of the chiral vectors which are also the directions that graphene sheets are rolled up. Due to their small scale and special structures, carbon nanotubes present interesting electrical, optical, mechanical, thermal, and toxic properties. Graphene nanoribbons can be viewed as strips cut from infinite graphene. Graphene nanoribbons can be either metallic or semiconducting depending on their edge structures. These are robust materials with excellent electrical conduction properties and have the potential for device applications. In this research project, we present a theoretical study of electrical properties of the carbon structures. Electronic band structures, density of states, and conductance are calculated. The theoretical models include a tight-binding model, a Green’s function methodology, and the Landauer formalism. We have investigated the effects of vacancy and weak disorder on the conductance of zigzag carbon nanoribbons. The resulting local density of states (LDOS) and conductance bands show that electron transport has interesting behavior in the presence of any disorder. In general, the presence of any disorder in the GNRs causes a decrease in conductance. In the presence of a vacancy at the edge site, a maximum decrease in conductance has been observed which is due to the presence of quasi-localized states. / Theory -- Band structure and density of states of carbon nanotubes -- Band structure and density of states of graphene nanoribbons -- Quantum conductance of zigzag graphene nanoribbons -- Quantum conductance of a zigzag graphene nanoribbon with defects. / Department of Physics and Astronomy

Research in carbon nanotubes (CNTs) has become a very active field in the past decades, with much interest in their electronic and mechanical properties. However, the thermal properties of CNTs are still not well understood, in particular the process of annealing; i.e. purification of samples by desorption of internal and external impurities. Understanding the response of carbon nanotubes to high temperatures is critical for proper characterization of CNTs and CNT-based materials; especially because purportedly non-destructive characterization techniques such as Raman spectroscopy can induce high temperatures through laser heating. This thesis delineates an experiment aimed at elucidating the annealing and destruction process of carbon nanotubes. The experiment consists of heat treatments of single-walled nanotubes (SWNTs), monitoring nanotube abundance and purity by Raman spectroscopy. The samples are HiPCO-produced SWNTs of very high purity, separated in open and closed (end-capped) tubes. They are wetted with H2O in order to fill the open tubes, but are otherwise kept in their raw (as-produced) form of flakes of bundled tubes. This means that they have a low thermal conductivity as compared to dispersed CNTs, making them sensitive to overheating. The samples are heated in both air and argon environments in order to study the effect of oxidation. It is found that all tubes exhibit some annealing after heat treatment at temperatures as low as 100 °C. Temperatures higher than that are sufficient to degrade the samples in the case of closed tubes, which are found to be more thermally sensitive than open tubes, especially in air environments as oxidation is found to be a major component of the destructive mechanisms of CNTs. With higher temperature heat treatments at 500 °C, some of the open tubes exhibit a further step of annealing. This correlates with tube diameter, thus indicating that this annealing step can be associated with the desorption water from the CNTs' interior. A transition is found after heat treatment at 600 °C, although the new phase is not conclusively established, with evidence pointing to either charge transfer (by way of intercalation of dopant atoms in CNTs) or graphitization.

Submitted in fulfillment of the requirements for the Degree of Master of Applied Science in Chemistry, Durban University of Technology, Durban, South Africa, 2016. / This study involves the development of a sensitive electrochemical biosensor for the determination of capsaicin extracted from chilli pepper fruit, based on a novel signal amplification strategy. The study therefore, seeks to provide a sensitive electro-analytical technique to be used for the determination of capsaicin in food and spicy products. Electrochemical measurements using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) modes were utilized in order to understand the redox mechanism of capsaicin and to test the performance of the developed biosensor supported with computational techniques. In this work two different enzymes, Phenylalanine ammonia lyase (PAL) and Glucose oxidase (GOx) were used for electrode modifications respectively. For this purpose three different types of working electrodes namely: glassy carbon electrode (GCE), platinum electrode (Pt-E) and gold electrode (Au-E) were used and their performances were compared. For the first time, the three electrodes were modified with PAL and GOx enzymes on multiwalled carbon nanotubes used in this study and characterized by attenuated total reflectance infrared spectroscopy, transmittance electron microscopy and thermo-gravimetric analysis supported by computational methods. The comparison of the results obtained from the bare and modified platinum electrodes revealed the sensitivity of the developed biosensor with modified electrode having high sensitivity of 0.1863 µg.L-1 and electron transfer rate constant (ks) of 3.02 s-1. To understand the redox mechanism completely, adsorption and ligand-enzyme docking simulations were carried out. Docking studies revealed that capsaicin formed hydrogen bonds with Glutamates (GLU355, GLU541, GLU586), Arginine (ARG) and other amino acids of the hydrophobic channel of the binding sites which facilitated the redox reaction for detection of capsaicin. These results confirm that the PAL enzyme facilitated the electron transfer from the capsaicin ligand, hence improving the biosensing response. Our results suggest potential applications of this methodology for the determination of capsaicin in the food industry. / M

Carbon nanotubes are known as ideal fillers for polymer systems; the main advantage of carbon nanotubes over other nano-reinforcing particles is the combination of superior strength and stiffness with large aspect ratio. Carbon nanotubes may improve the mechanical, electrical and thermal properties of polymers, but to realise their potential in polymer systems uniform dispersion, strong interfacial adhesion and alignment of nanotubes within the polymer matrix are necessary. These properties are not easy to achieve and they are key challenges in producing CNT/Polymer system. This research was carried out in an attempt to understand how the properties of CNT/Polymer composite can be optimised by manipulation of additives, compounding and postcompounding conditions. Polypropylene/Multi-Walled Carbon Nanotube (PP/MCNT) composites were prepared by conventional twin screw extrusion. Dispersants and compatibilisers were used to establish good interaction between filler and polymer. Several different extruder screw configurations were designed and the properties of PP/MCNT composite prepared by each configuration investigated. The results indicated that the addition of carbon nanotubes without additives enhanced mechanical, electrical and thermal properties of polypropylene polymer. Incorporation of compatibilisers into PP/MCNT improved the stiffness but decreased the strength of the nanocomposite, whilst addition of dispersants decreased the mechanical properties of the nanocomposite. Addition of both additives at high concentration improved electrical conductivity and induced electrical percolation in the nanocomposite. Extruder screw configuration was found to have significant effect on the electrical conductivity whilst only slightly affecting mechanical properties of the nanocomposite, possibly due to the competition between dispersion and degradation of polymer chains and possible reduction of carbon nanotube length by intensive shear during compounding. The use of screw configuration with high mixing intensity promoted the dispersion of nanotubes and favoured the conduction process in the nanocomposite. Finally in an attempt to improve dispersion and alignment of carbon nanotubes, compounded PP/MCNT composite was subjected to micromoulding, fibre spinning and biaxial stretching processes and the resultant properties investigated. Application of post-compounding process was found to have significant effect on mechanical and rheological properties of the nanocomposite. Stiffness and strength of the nanocomposites treated by post-compounding processes were found to increase by up to 160% and 300%, respectively. The reinforcement effect of carbon nanotubes in the stretched nanocomposites was found to be the greatest. Rheological analysis suggested that the application of post-compounding processes enhanced dispersion of carbon nanotubes within the nanocomposite. Overall, this finding of this research has shown that carbon nanotubes can be incorporated into polypropylene using conventional equipment to provide significant improvement in properties. By careful choices of additives, compounding and postcompounding conditions, specific properties can be further enhanced.

Doctor of Philosophy / Department of Chemistry / Duy H. Hua / The first chapter of the thesis involves the design, synthesis, and anti-influenza activity of quercetin derivatives. Influenza viruses are important pathogens that cause respiratory infections in humans and animals. In addition to vaccination, antiviral drugs against influenza virus play a significant role in controlling viral infections by reducing disease progression and virus transmission. Plant derived polyphenols are associated with antioxidant activity, anti-carcinogenic, and cardio- and neuro-protective actions. Some polyphenols, such as resveratrol and epigallocatechin gallate (EGCG), showed significant anti-influenza activity in vitro. The antiviral effects of isoquercetin were greater than that of quercetin with lower IC[subscript]5[subscript]0 values and higher in vitro therapeutic index. Various phenolic esters, alkoxy and aminoalkoxy derivatives of quercetin were synthesized by functionalization of C3, C3’, and C5 hydroxyl groups. Antiviral activities of these synthesized compounds were tested against influenza virus (porcine H1N1 strain). Quercetin-3-gallate which is structurally similar to EGCG showed greater antiviral activity among the synthesized compounds. Its antiviral activity was comparable to that of EGCG with better in vitro therapeutic index. Second chapter in the thesis involves the progress towards the synthesis of mini graphenes like hexa-peri-benzocoronene cyclophane (HBCC). Bilayered graphenes are highly conducting materials with potential application in electronic devices and in lithium ion batteries. Despite great potential, bilayer graphenes with defined distance between the two layers have not been achieved through chemical synthesis. Chemical synthesis of hexa-peri-benzocorenene cyclophane (HBCC) from commercially available p-xylene was carried out. Final product, presumably compound 90 (the structure has not been completely characterized), is insoluble in all tested solvents including aqueous acids and organic solvents such as DMSO, DMF, benzene, 1,2-dichlorobenzene, dichloromethane, THF, hexanes and diethyl ether. The insoluble nature of the final product restricted the analysis to UV-visible spectroscopy. Synthesis of soluble analog incorporating the long chain ether groups is being investigated in Dr. Hua’s laboratory.

En raison des propriétés physiques, électriques, mécaniques et chimiques exceptionnelles, les nanotubes de carbone(CNTs) sont considérés comme l'un des nanomatériaux les plus importants aujourd'hui. CNTs peuvent être classées comme des nanotubes de carbone à paroi simple (SWCNTs) ou des nanotubes de carbone à parois multiples (MWCNTs). La structure d'un SWCNT peut être vue comme une couche d’un atome de graphite de cylindres laminés. Les propriétés des SWCNTs sont fondamentales pour la recherche et pour de nombreuses applications en médecine, en électronique, en environnement, pollution... Le but de cette thèse est d'étudier les propriétés mécaniques et électromécaniques des matériaux SWCNTs avec différentes morphologies. Nous avons étudié les propriétés élastiques des SWCNTs individuels en utilisant la méthode des éléments finis (FE). Nous avons montré que les modules élastiques de SWCNTs dépendent du diamètre, chiralité et la longueur. Les modules élastiques augmentent significativement selon les plus petites valeurs du rayon. Lorsque le rayon devient plus grand, tous les modules élastiques convergent vers une valeur constante asymptotique. En outre, les modules de zigzag et SWCNT chirales sont plus sensibles à la variation du rayon par rapport à SWCNT fauteuil. Nous avons testé le module élastique de SWCNT film mince par nanoindentation. Nous avons trouvé que le module d'Young E et la dureté H de SWCNT film mince sont séparément E= 192.831± 13.922 GPa, H=12.57719 ± 0.759 GPa. Nous avons élaboré un modèle par éléments finis qui représente le comportement des SWCNT film mince dans le processus de nanoindentation. Dans cette étude nous avons élaboré un modèle élasto-plastique pour décrire le comportement mécanique du matériau au cours de l'indentation. Ensuite, nous avons évalué les propriétés élasto-plastiques de SWCNT film mince par l’interaction de la simulation par éléments finis avec les données statistiques du test expérimental. Le modèle bilinéaire proposé approxime bien la performance de SWCNT film mince dans la nanoindentation. Finalement, nous avons étudié les propriétés électrostrictives du composite (P (VDF-TrFE) / SWCNT) à base de SWCNTs par la méthode des éléments finis. Les résultats numériques trouvés montrent que l'électrostriction du composite SWCNT / P (VDP-TrFE) est considérablement dépendant de la fraction volumique de SWCNT et du rapport des constantes diélectriques (SWCNT et P (VDP-TrFE)). Dans ce travail, nous avons constaté que les propriétés des CNTs obtenues théoriquement ou expérimentalement impliquent des inévitables incertitudes. Donc la prise en compte des incertitudes des propriétés des CNTs devient nécessaire. Pour l’analyse de ces incertitudes, nous avons appliqué la méthode de l'optimisation basée sur la fiabilité (RBO). Cette méthode est un outil efficace pour assurer la fiabilité des résultats expérimentaux et numériques dans le processus d'estimation du comportement élasto-plastique pour SWCNT film mince. / Carbon nanotubes (CNTs) as one of the most important nanomaterials today have been demonstrated a combination of exceptional physical, electrical, mechanical, and chemical properties, which have resulted in their great potential of industrial application in many fields. CNTs can be categorized as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The structure of a SWCNT can be viewed as one-atom-thick layer of graphite rolled cylinder. Well understand the property of SWCNTs is fundamental in the exploration of research and applications of CNTs based products.The present research is focus on evaluating the mechanical and electromechanical properties of SWCNTs materials with different material morphology. Under the hierarchical (or bottom-up) ideal, the elastic properties of the individual SWCNTs were studied by using Finite element (FE) method. Effects of the diameter, chirality and length on the elastic moduli of SWCNTs are discussed based on numerical calculations. Furthermore, the ultra-thin SWCNTs film (~200nm) is prepared by spin coating method. The elastic modulus of SWCNT thin film is estimated by nanoidentation test. Its elasto-plastic properties were then determined by FE simulation combined with the statistics constraints of the experimental results. The results showed that the mechanical performance of SWCNTs thin film during indentation can be approximately represented by a bilinear model. The mechanical parameters of SWCNTs thin film obtained by experiment and numerical calculation are : the Young’s modulus E=192.83± 13.922 Gpa, the tangent modulus Et ≈ 42GPa, and the yield stress Oy ≈ 8.4GPa, respectively. The electrostrictive properties of SWCl\lT- based composite (P(VDF-TrFE)/SWCNT) were also investigated by FE method. Numerical results show that the electrostriction of the SWCNT/P(VDP-TrFE) composite is greatly dependent on the volume fraction of SWCNT and the difference of dielectric constant between SWCNT and P (VDP-TrFE) copolymer. In this work, we found that the properties of CNTs obtained either by theory or by experiments involve inevitable uncertainty, and some are relatively large. Therefore, uncertainty analysis for the predicted properties of CNTs becomes necessary with the increasing product performance demands. The application of Reliability-Based Optimization (RBO) method in the process of elasto-plastic behavior estimation for SWCNT thin film indicates that RBO method should be an effective tool to ensure the reliability of experimental and numerical results.

Um desafio central na área das ciências da saúde e biomédica tem sido o desenvolvimento de testes clínicos embasados em novas tecnologias que resultem em medidas precisas, com resultados consistentes mais rápidos que os convencionais, e ao menor custo possível. Os esforços atuais têm se concentrado em integrar a análise de materiais biológicos a componentes de circuitos integrados compatíveis com a indústria de semicondutores existente. Nesse contexto, esse trabalho apresenta duas contribuições a partir do uso de materiais nanoestruturados alótropos do carbono. Primeiramente, demonstramos como o desempenho de um sensor de pH embasado na tecnologia EGFET (Extended Gate Field Effect Transistor) pode ser controlado com a incorporação de grafenos, com diferentes graus de funcionalização, a eletrodos de FTO (Fluorine doped Tin Oxide). Os eletrodos de FTO foram modificados através da deposição dos materiais nanoestruturados de carbono via eletroforese. O desempenho dessas amostras como sensor de íons H+ mostrou dependência quanto ao tempo de deposição e composição tampão utilizado, tendo seu desempenho aumentado em até 24%, atingindo uma sensibilidade máxima de 67 mVopH-1 para tampão fosfato. A segunda contribuição desse trabalho trata-se da combinação das informações obtidas com um arranjo de dispositivos de NTFETs (Nanotubes Field Effect Transitors) decorados com nanopartículas metálicas e análise de discriminantes lineares, empregados na classificação de diferentes populações celulares. O método proposto foi capaz de identificar e classificar corretamente entre as linhagens de células cancerígenas B16 (melanoma), 3LL (carcinoma) e 3L4 (linfoma), além de distingui-las corretamente de suas contrapartes saudáveis. Adicionalmente, utilizamos esse conjunto de dados para classificar uma população celular desconhecida, demonstrando uma possível utilidade clínica da metodologia desenvolvida. / A central challenge in the biomedical field has been the development of new approaches for clinical tests based on microelectronic technologies, aiming trustful and precise results, faster and cheaper than the standard techniques. Current efforts have focused on integrating the analysis of biological samples and integrated circuit components compatible with the standard semiconductor industry. In this context, the present work gives two contributions on the usage of carbon nanostructure allotropes. First, we show how the performance of pH sensors based on EGFET (Extended Gate Field Effect Transistor) can be tuned with the integration of graphene nanosheets, with different degrees of functionalization, into FTO (Fluorine doped Tin Oxide) electrodes. The FTO electrodes were modified through EPD (electrophoretic deposition) of the carbon nanomaterials. The device performance as pH sensor showed dependence on the time of deposition and buffer composition, increasing up to 24% compared to the bare FTO electrode and reaching a maximum sensitivity of 67 mVopH-1 for phosphate buffer. The second contribution of this work regard the combination of the data gathered using an array of NTFETs (Nanotube Field Effect Transistors) decorated with metal nanoparticles and LDA (Linear Discriminant Analysis) to distinguish among different cell populations. The proposed method correctly classifies among the cancer cell lines B16 (melanoma), 3LL (carcinoma), and 3L4 (lymphoma), as well as cancer cells from their healthy counterparts. Additionally, we demonstrated a possible application of the method correctly classifying blind samples.

La chimie d'interface du diazonium a progressé au cours des dernières années et s'est pratiquement impliquée dans tous les domaines de la science et technologie des matériaux. L’utilisation des sels de diazonium est justifiée par le fait qu’ils adhèrent aux surfaces avec de fortes énergies de liaison, en particulier sur le carbone sp², ce qui en fait d’excellents agents de couplage pour les polymères aux surfaces. Dans ce contexte, nous avons travaillé sur deux types de nanohybrides de nanotubes de carbone (NTC) : NTC-polytriazole (NTC-PTAz) et NTC-colorant. Le nanohybride NTC-PTAz a été synthétisé par polymérisation « click » en surface. Pour ce faire, les NTCs ont été greffés de groupes 4-azidophényle à partir du sel de diazonium correspondant. Le NTC modifié (NTC-N3) a servi de support pour une polymérisation confinée en surface de type polyaddition générant ainsi le nanohybride NTC-PTAz. Ce matériau a été caractérisé par ATG, XPS, IR et Raman. Ses applications potentielles sont dans le développent d’adsorbants de métaux lourds, l’immobilisation de nanocatalyseurs ou pour le stockage des gaz. La seconde partie de la thèse est plus étoffée et porte sur les nanotubes de carbone greffés de colorants diazotés Rouge Neutre (NR), Azure A (AA) et Rouge Congo (CR). L’analyse fine de ces matériaux a révélé une très forte adhésion des colorants aux NTCs et les couches superficielles ont des épaisseurs de 2 à 6 nm, sont homogènes et continues. Les NTC-colorant ont été incorporés dans des matrices élastomères de type EVA pour la réalisation d’actionneurs opto-thermiques implantés dans des pads pour non-voyant. Dans les matrices EVA, les NTCs greffés de colorants servent à capter la lumière et induire un changement de forme dans le pad qui soit palpable par le non voyant (250 µm). Les matrices EVA renforcées de nos nanotubes greffés de colorants ont été réalisées et testées par analyse mécanique dynamique. Les composites NTC/colorant-EVA sont flexibles et prometteurs pour le développement de nouveaux types des pads tactiles pour les non-voyants. Les nanohybrides NTC-NR ont servi comme capteurs chémo-résistifs pour la reconnaissance moléculaire de l’acétone.Dans une dernière application, le nanohybride CNT-CR a été étudié en tant qu’électrocatalyseur pour l’oxydation directe du méthanol. Des résultats intéressants ont été obtenus avec ces nanohybrides mais des améliorations significatives (rapport 3) des propriétés électrocatalytiques ont été obtenues avec des CNT-CR décorés avec des nanoparticules d'or. Le système électrocatalytique nouvellement conçu pourrait être considéré pour différentes applications prometteuses, notamment les capteurs, les biocapteurs, les catalyseurs hétérogènes pour les piles à combustible. Pour résumer, les nanohybrides à base de CNT nouvellement conçus présentent des performances uniques attribuées à la polyvalence de la chimie d'interface du diazonium pour la fixation efficace de couches moléculaires et macromoléculaires fonctionnelles. Les nanohybrides novateurs servent de blocs de construction pour la conception de matériaux nanocomposites à hautes performances potentiellement utiles dans les nouveaux défis socio-économiques tels que l’environnement, la biomédecine et l’énergie / Diazonium interface chemistry has progressed over the last few years and practically involved in all areas of materials science and engineering. The rationale for employing diazonium salts is that they attach to surfaces with remarkable bond energies, particularly on sp² carbon materials, making them an ideal coupling agent for polymers to surfaces In this context, novel CNT-polytriazole (CNT-PTAz) and CNT-dye nanohybrids were designed and thoroughly characterized. First, CNT-PTAz nanohybrid was prepared by click polymerization: multiwalled carbon nanotubes (CNTs) were modified with azidophenyl groups (CNT-N3) from 4-azidobenzenediazonium precursor and served as nanoscale platform for the surface confined polyaddition. The CNT-PTAz nanohybrid was characterized by TGA, XPS, IR, and Raman. The robust CNT-PTAz is robust and has potential in developing heavy metal adsorbents, nanosupport for catalysts or for gas storage. In the second major part, we grafted CNT with diazotized Neutral red (NR), Azure A (AA) and Congo Red (CR) dyes by simple, spontaneous reaction of the diazonium salts and CNTs in water, at RT. A thorough investigation of the nanohybrids showed that the adhesion is strong (CNT-dye C-C bond energy higher than 150 kJ/mol), and the layer is uniform. These nanohybrids further served to reinforce ethylene-vinyl acetate (EVA) an elastomeric matrix. The reinforced matrix is flexible and serves as optothermal actuators where the grafted dye catches the light to induce mechanical changes in the matrix monitored by dynamic mechanical analysis. CNT/dye-reinforced EVA is a promising flexible composite for developing new types of visual-aid tablet for visually impaired people. The versatile CNT-dye nanohybrids are also unique chemiresistive gas sensors for the molecular recognition of acetone vapours. In a final application, CNT-CR nanohybrid was investigated as an electrocatalyst for the Direct Oxidation of Methanol. Interesting results were obtained with these nanohybrids but significant improvements (3-fold) of the electrocatalytic properties were achieved with CNT-CR decorated with gold nanoparticles. The newly designed electrocatalytic system could be regarded for different promising applications most likely as for sensors, biosensors, heterogeneous catalysts for fuel cells and for nanotechnology To summarize, newly designed CNT-based nanohybrids have unique performances ascribed to the versatility of the diazonium interface chemistry in efficiently attaching functional molecular and macromolecular layers. The novel nanohybrids serve as building blocks for designing high performance nanocomposite materials relevant to challenging timely social economic issues, namely environment, biomedicine and energy

Thesis advisor: David A. Broido / A theory is presented for describing the lattice thermal conductivities of graphene and single-walled carbon nanotubes. A phonon Boltzmann transport equation approach is employed to describe anharmonic phonon-phonon, crystal boundary, and isotopic impurity scattering. Full quantum mechanical phonon scattering is employed and an exact solution for the linearized Boltzmann transport equation is determined for each system without use of common relaxation time and long-wavelength approximations. The failures of these approximations in describing the thermal transport properties of nanotubes is discussed. An efficient symmetry based dynamical scheme is developed for carbon nanotubes and selection rules for phonon-phonon scattering in both graphene and nanotubes are introduced. The selection rule for scattering in single-walled carbon nanotubes allows for calculations of the thermal conductivities of large-diameter and chiral nanotubes that could not be previously studied due to computational limitations. Also due to this selection rule, no acoustic-only umklapp scattering can occur, thus, acoustic-optic scattering must be included in order to have thermal resistance from three-phonon processes. The graphene selection rule severely restricts phonon-phonon scattering of out-of-plane modes. This restriction leads to large contributions to the total thermal conductivity of graphene from the acoustic, out-of-plane modes which have been previously neglected. Empirical potentials used to model interactions in carbon-based materials are optimized to better describe the lattice dynamics of graphene-derived systems. These potentials are then used to generate the interatomic force constants needed to make calculations of the thermal conductivities of graphene and carbon nanotubes. Calculations of the thermal conductivities of single-walled carbon nanotubes and graphene for different temperatures and lengths are presented. The thermal conductivities of SWCNTs saturate in the diffusive regime when the effects of higher-order scattering processes are estimated and correctly reproduce the ballistic limit for short-length nanotubes at low temperatures. The effects of isotopic impurity scattering on the thermal conductivities of graphene and SWCNTs are explored. Isotopic impurities have little effect in the low (high) temperature regime where boundary (umklapp) scattering dominates the behavior of the thermal conductivities. In the intermediate temperature regime, modest reductions in the thermal conductivities, 15-20%, occur due to impurities. The thermal conductivities of a wide-range of SWCNTs are explored. The thermal conductivities of successively larger-diameter, one-dimensional nanotubes approach the thermal conductivity of two-dimensional graphene. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.