Orientador: Marcelo Orgaghi Orlandi / Banca: Maria Aparecida Z. Bertochi / Banca: Sonia Maria Zanetti / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Nos últimos anos, o interesse pelos materiais nanoestruturados vem permitindo que esta seja uma das áreas de maior evolução científica. O estudo das propriedades destes materiais caminha em passos largos e os resultados indicam que existem muitas vantagens em se utilizar materiais em escala reduzida. Neste trabalho, nanoestruturas de óxido de estanho foram sintetizadas pelo método de redução carbotérmica a fim de verificar o comportamento desses materiais como sensores de gás. Os materiais coletados após as sínteses foram caracterizados por difração de raios X (DRX), microscopia eletrônica de varredura de alta resolução (MEV-FEG), microscopia eletrônica de transmissão (MET), análise de área de superfície específica (BET), espectroscopia de absorção na região do ultravioleta e do visível (UV-Vis) e medidas elétricas em corrente contínua. Os resultados mostraram que o controle da atmosfera de síntese permite obter nanoestruturas de óxido de estanho com diferentes estados de oxidação (SnO, SnO2 e Sn3O4). Pelas análises por MEV-FEG foi possível observar que o material crescido na fase SnO é constituído por nanofitas e discos enquanto os materiais crescidos nas fases SnO2 e Sn3O4 são constituídos unicamente por nanofitas. As análises por MET mostraram que os materiais sintetizados são monocristalinos e não apresentam defeitos superficiais aparentes. A partir dos resultados das análises por BET, verificou-se que os materiais têm baixa área superficial devido à ausência de poros na superfície das nanoestruturas. Por meio dos espectros de UV-Vis foi observado que os materiais crescidos em diferentes fases apresentam valores distintos de bandgap. A caracterização elétrica dos materiais permitiu analisar o comportamento das nonoestruturas como sensor de NO2, H2 e CO e os resultados... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In recent years the interest in nanostructured materials has permited it to be an area of great scientific developments. The study of properties of these materials moving in leaps and bounds and results show that there are many advantages in using small-scale materials. In this study were synthesized tin oxide nanostructures by carbothermal reduction method to verify the behavior of these materials as a gas sensor. The materials collected after the synthesis were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), analysis of specific surface area (BET), ultraviolet and visible absorption spectroscopy (UV-Vis) and dc electrical measurements. The results showed that by control synthesis atmosphere it is possible to obtain tin oxide nonomaterials with different oxidation states (SnO, SnO2 and Sn3O4). By FEG-SEM analysis it was observed that the material grown on SnO phase consists of nanoribbons and disks while the grown materials in SnO2 and Sn3O4 phases consist solely of nanoribbons. The TEM analysis showed that the materials synthesized are monocrystalline and show no apparent surface defects. From the results of analyzes by BET, it was found that the materials exhibit low values of surface area due to absence of porous on the surface of nanostructures. Through UV-Vis spectra was observed that the materials grown in different phases have different values of bandgap. The electrical characterization of materials enabled to analyze the behavior of the nanostructures as NO2, H2 and CO sensors and the results showed that all materials exhibit n-type semiconductor behavior and a sensitivity and response time dependent on the concentration of gas and temperature. The best results were achieved when the nanostructures (especially SnO disks) were exposed to NO2 at temperatures... (Complete abstract click electronic access below) / Mestre

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2007. / The continuous development of new materials and the improvement of existing ones ensure a balance between technological growth and environmental sustainability. With the above trade-offs, the quality of life for humankind is continually being improved. Polymeric materials are some of our most valued commodities in our everyday lives. They continue to be developed and improved in a variety of ways; one of which is to improve their properties by preparing nanocomposites. Polymer-based nanocomposites (PNCs) is a way of getting novel properties and enhancing existing one in polymer matrices, by incorporating additives on a nano-scale. The most significant advantage of PNCs is the potential to design and tailor properties for a specific application, since the control of the structure can be done at the molecular level. Therefore, a fundamental understanding of the relationships between the structure and the properties of PNCs is of utmost importance. Amongst the most studied and researched PNC materials, polymer-layered silicate nanocomposites (PLSNs) have recently enjoyed attention from academia and industry. In the current study structure-property relationships of PLSNs were investigated. Polystyrene (PS) was chosen as the base polymer due to its wide use in many articles such as in packaging. It was also a material of choice based on its poor mechanical properties in its natural state (unfilled), so as to contribute in its property improvement. Montmorillonite (MMT) was a layered silicate (clay) of choice, as much research has been done on it, and it is available worldwide, as a main component in Bentonite (a natural material). Clays are composed of sheet-like, layered particles, which, when in a suitable environment, can delaminate into single, nano-sized sheets. The sheets are held together by van der Waals forces and between the sheets are exchangeable cations. The clays are hydrophilic in nature and cannot readily delaminate in a hydrophobic polymer matrix due to the differences in surface energies. A MMT surface was functionalized to be hydrophobic by conducting an ion exchange reaction with alkyl ammonium surface active agents (surfactants). Polymerizable surfactants (surfmers) were used to enhance the interfacial interaction between the PS matrix and MMT silicate layers. The organically modified clays (organoclays) were used in synthesizing polystyrene-layered silicate nanocomposites (PS-LSN) by an in-situ intercalative polymerization method. The polymerization of the nanocomposites was conducted in bulk. The morphologies of the nanocomposites were characterized using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (Ope). The study was further expanded to the investigation of the effects of the nanocomposite structure, type of organic modifier, and amount of clay loading on the properties of the materials. The properties were studied by dynamic mechanical analysis (DMA), thermomechanical analysis (TMA) and dielectric analysis (DEA). The properties were dependent on the interfacial processes between the clay layers and the polymer matrix. The changes in properties compared to the PS homopolymer showed time and temperature dependent effects, as determined by DEA. Even though the dynamics of the interfacial interactions are still not fully understood, the nanocomposites showed improvements in properties compared to the homopolymers.

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-13Bitstream added on 2014-06-13T20:20:41Z : No. of bitstreams: 1 silva_ra_me_bauru.pdf: 2068525 bytes, checksum: 90877fd5381cdf77dcbef03fb36865aa (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O trabalho objetiva a realização do crescimento de materiais nanoestruturados de óxido de zinco (ZnO) pelo método de redução carbotérmica e um estudo de suas propriedades como sensor, utilizando ZnO e distintas fontes de carbono (grafite e negro de fumo) como materiais de partida. Para efeito de comparação, o método hidrotermal assistido por micro-ondas (HAM) também foi utilizado como processo de síntese das nanoestruturas. Os materiais obtidos das sínteses foram caracterizados por difração de raios X (DRX), microscopia eletrônica de varredura com canhão de emissão por campo (MEV-FEG), além de microscopia eletrônica de transmissão (MET). Por meio destas técnicas de caracterização, mostrou-se a eficiência da obtenção de nanoestruturas de óxido de zinco, sendo que a morfologia do material resultante é fortemenete dependente do método utilizado. Testes para sensor de gás e luz foram realizados em amostras selecionadas utilizando como critério sua morfologia nanométrica e uniformidade de crescimento. Para medidas com gás, utilizou-se o oxigênio e também o hidrogênio. A medida foi realizada em uma câmara hermeticamente fechada com controle da temperatura e do fluxo dos gases, onde foi inserido um eletrodo interdigital de alumina com trilhas de contato de ouro para qual foi utilizado para depositar as estruturas de ZnO. Para alimentação do sistema, foi utilizada uma fonte de tensão estabilizada, que é operada remotamente e tem sensibilidade na medida da corrente em picoampére, possibilitando assim maior precisão nas medidas. Para as medidas de sensor de luz, foi utilizado o mesmo eletrodo interdigital supracitado, mas o material foi exposto a uma lâmpada de xenônio com intensidade equivalente à metade da intensidade da luz solar. Com relação às medidas das propriedades como sensor de gás e luz, foram analisados parâmetros como: resposta de sensor, sinal, sensibilidade e tempo de resposta / The work aims to conduct a study on the growth of nanostructured materials of zinc oxide (ZnO) by carbothermal reduction process and its sensor properties for both gas and light stimulus. For comparison, the microwave-assisted hydrothermal method (MAH) was also used as synthesis process of nanostructures. The synthesizes materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM). Through these characterization techniques it was showed that synthesis methods are efficient, and the morphology of the resulting materials depends on the method used. Sensor tests were performed for some samples, using a selection criteria the size and morphology of the material. For sensor characterization it was used hydrogen and oxigen gases. A sealed chamber with controlled temperature and gas flow was used to perform the measurements, whichwas connected to a stabilized voltage source. This source is operated remontly and has a sensibility in the current measurement of picoampére, allowing greater accuracy in the measurement. For the deposition ZnO nanostructures, was used an Alumina interdigital electrode with tracks of gold contact. To measure the light sensor, the same electrode above mentioned was exposed to the beam with an intensity of half of sun radiation (xenon lamp). Regarding the sensor properties (gas ans radiation) it was analyzed the response of the sensor, signal, sensibility and response time, which are essential parameters for the efficiency a sensor material. Through analysis of sensor measurements, it was found that the samples synthesized by HAM had batter sensor performance than the obtained by carbothermal reduction process

Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-03-27Bitstream added on 2014-06-13T19:00:08Z : No. of bitstreams: 1 suman_ph_me_bauru.pdf: 8662064 bytes, checksum: f9b4c3f0d58b2511c3daba558e51dec2 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nos últimos anos, o interesse pelos materiais nanoestruturados vem permitindo que esta seja uma das áreas de maior evolução científica. O estudo das propriedades destes materiais caminha em passos largos e os resultados indicam que existem muitas vantagens em se utilizar materiais em escala reduzida. Neste trabalho, nanoestruturas de óxido de estanho foram sintetizadas pelo método de redução carbotérmica a fim de verificar o comportamento desses materiais como sensores de gás. Os materiais coletados após as sínteses foram caracterizados por difração de raios X (DRX), microscopia eletrônica de varredura de alta resolução (MEV-FEG), microscopia eletrônica de transmissão (MET), análise de área de superfície específica (BET), espectroscopia de absorção na região do ultravioleta e do visível (UV-Vis) e medidas elétricas em corrente contínua. Os resultados mostraram que o controle da atmosfera de síntese permite obter nanoestruturas de óxido de estanho com diferentes estados de oxidação (SnO, SnO2 e Sn3O4). Pelas análises por MEV-FEG foi possível observar que o material crescido na fase SnO é constituído por nanofitas e discos enquanto os materiais crescidos nas fases SnO2 e Sn3O4 são constituídos unicamente por nanofitas. As análises por MET mostraram que os materiais sintetizados são monocristalinos e não apresentam defeitos superficiais aparentes. A partir dos resultados das análises por BET, verificou-se que os materiais têm baixa área superficial devido à ausência de poros na superfície das nanoestruturas. Por meio dos espectros de UV-Vis foi observado que os materiais crescidos em diferentes fases apresentam valores distintos de bandgap. A caracterização elétrica dos materiais permitiu analisar o comportamento das nonoestruturas como sensor de NO2, H2 e CO e os resultados... / In recent years the interest in nanostructured materials has permited it to be an area of great scientific developments. The study of properties of these materials moving in leaps and bounds and results show that there are many advantages in using small-scale materials. In this study were synthesized tin oxide nanostructures by carbothermal reduction method to verify the behavior of these materials as a gas sensor. The materials collected after the synthesis were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), analysis of specific surface area (BET), ultraviolet and visible absorption spectroscopy (UV-Vis) and dc electrical measurements. The results showed that by control synthesis atmosphere it is possible to obtain tin oxide nonomaterials with different oxidation states (SnO, SnO2 and Sn3O4). By FEG-SEM analysis it was observed that the material grown on SnO phase consists of nanoribbons and disks while the grown materials in SnO2 and Sn3O4 phases consist solely of nanoribbons. The TEM analysis showed that the materials synthesized are monocrystalline and show no apparent surface defects. From the results of analyzes by BET, it was found that the materials exhibit low values of surface area due to absence of porous on the surface of nanostructures. Through UV-Vis spectra was observed that the materials grown in different phases have different values of bandgap. The electrical characterization of materials enabled to analyze the behavior of the nanostructures as NO2, H2 and CO sensors and the results showed that all materials exhibit n-type semiconductor behavior and a sensitivity and response time dependent on the concentration of gas and temperature. The best results were achieved when the nanostructures (especially SnO disks) were exposed to NO2 at temperatures... (Complete abstract click electronic access below)

M.Tech. (Chemistry) / Please refer to full text to view abstract

Ces travaux de thèse portent sur le développement d’un dispositif de synthèse de nanoparticules (NPs) par une voie physique basée sur la pulvérisation laser d’une cible suivie d’une trempe du panache plasma ainsi formé. L’association de cette source à une enceinte d’ablation laser conventionnelle a permis de synthétiser des NPs d’argent et de vanadium empilées sur des substrats ou noyées dans des matrices synthétisées par ablation laser. Des analyses par microscopie électronique en transmission (MET) et microscope à force atomique (AFM) ont révélé des NPs cristallisées en vol, de forme sphérique et de tailles relativement monodisperses (~ 3 nm de diamètre) fonction de leur temps de séjour dans la cavité de nucléation. La réalisation de nanocomposites Al2O3 amorphe dopée par des NPs d’argent métallique de différentes tailles a montré l’influence de la taille de ces entités nanométriques sur la position et la largeur de la résonance plasmon de surface (RPS) du matériau nanostructuré. Les NPs gardent leur forme originelle après impact sur le substrat ce qui conduit à des empilements de nanoparticules fortement poreux (de l’ordre de 50%). Des NPs de dioxyde de vanadium ont pu être synthétisées par recuit d’empilements de NPs de vanadium. Du fait de leur individualité, les NPs de VO2 présentent une température de transition plus faible (~50°C) et une largeur d’hystérésis plus importante (~10-30°C) qu’un film mince (température de transition d’environ 68°C et largeur d’hystérésis d’environ 3°C). En associant un film mince synthétisé par PLD à un empilement de NPs il est alors possible de combiner leurs propriétés et d’obtenir un matériau nanocomposite présentant une transition par palier. / The work presented in this thesis is focused on the development of an experimental setup for the synthesis of nanoparticles (NPs) by a physical route, based on the laser vaporization of a target and followed by the rapid quenching of the plasma plume. Combining such a NP source with conventional laser ablation makes possible to synthesize silver and vanadium NPs in stacks on substrates or embedded in different matrices synthesized by laser ablation. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis revealed crystallized spherical NPs relatively monodisperse in size (~ 3 nm in diameter) depending on the residence time in the nucleation cavity. The synthesis of amorphous Al2O3 nanocomposites doped with metallic silver NPs of different sizes showed the influence of the size on the position and the width of the surface plasmon resonance (SPR) of the nanostructured material. The NPs keep their original shape during impact on the substrate, leading to highly porous NPs stacks (approximately 50%). Vanadium dioxide nanoparticles (VO2 NPs) have been synthesized by annealing vanadium NPs stacks. Due to their individual behaviour, VO2NPs exhibit lower transition temperature (~ 50°C) and larger hysteresis width (~ 10-30°C) than thin films (transition temperature around 68°C and hysteresis width around 3°C). By coupling a PLD thin film and a NPs stack, it is possible to combine their properties and obtain a nanostructured material having a step transition.

Les travaux réalisés au cours de cette thèse traitent et misent en avant l’effet d’associer différents types d’argiles organophiles OMMT (Cloisite®15A et Cloisite®30B) avec le graphène fonctionnalisé époxy (Gr) sur l’ensemble des propriétés fonctionnelles des matrices biodégradables polyacide lactique (PLA), poly (ε-caprolactone) (PCL) et leur mélange PLA/PCL de composition 70/30. Le premier volet est consacré à l’étude des mélanges binaires (PLA/Cloisite® et PLA/Gr) et ternaires (PLA/Cloisite®/Gr) préparés à l’état fondu. L’association des deux renforts OMMT/Gr a amélioré l’ensemble des paramètres rhéologiques de la matrice PLA et contribue à l’apparition d’un comportement viscoélastique pseudo-solide pour les mélanges PLA/Gr en présence des argiles, attribué à un meilleur état de dispersion des couples confirmé par la microscopie électronique à transmission. Les propriétés barrières à la vapeur d’eau, thermiques et thermomécaniques du PLA ont été sensiblement améliorées, particulièrement en présence des couples de nanocharges OMMT/Gr et montrent le grand intérêt des nanobiocomposites PLA/Cloisite®/Gr dans plusieurs applications. La seconde partie est liée aux matériaux nanocomposites à base de la matrice PCL. L’étude rhéologique a confirmé l’intérêt de combiner les nanocharges OMMT et graphène et indique la présence de réseaux 3D dans les nanocomposites PCL/OMMT et PCL/OMMT/Gr. La bonne dispersion des nanocharges a nettement amélioré les propriétés barrières à la vapeur d’eau et la tenue thermique de la PCL. La dispersion des nanocharges et leurs effets sur la miscibilité a fait l’objet de la dernière partie consacrée aux matériaux à base du mélange immiscible PLA/PCL. Des propriétés viscoélastiques très intéressantes ont été obtenues après l’incorporation des mélanges OMMT/Gr, indiquant l’existence d’un bon niveau de distribution des renforts dans la matrice PLA/PCL. La synergie existante entre les nanocharges OMMT et graphène fonctionnalisé époxy a conduit à l’amélioration des propriétés barrières, de la stabilité thermique et de la miscibilité de la matrice. / The work carried out during this thesis highlights the effect of different kinds of organophilic clays OMMT (Cloisite®15A and Cloisite®30B) and/or epoxy functionalized graphene (Gr) on the functional properties of biodegradable polylactic acid (PLA), poly (ε-caprolactone) (PCL) and their mixture PLA/PCL (70/30 mass%). The first part is devoted to study the binary mixtures (PLA/Cloisite® and PLA/Gr) and ternary materials (PLA/Cloisite®/Gr) prepared via melt blending method. The combination of the two fillers (OMMT and Gr) improves all the rheological parameters of the PLA matrix and contributes to the appearance of a pseudo-solid viscoelastic behavior for PLA/Gr composites in the presence of clays, attributed to the better dispersion confirmed by transmission electron microscopy. The water vapor permeability, thermal and thermomechanical properties of PLA have been significantly improved, especially in the presence of hybrids OMMT/Gr and show the great interest of PLA/Cloisite®/Gr ternary nanobiocomposites in several applications. The second part is related to nanocomposite materials based on the biodegradable PCL matrix. The rheological study confirms the advantage of combining the organomodified clays and graphene nanofillers, and indicates the presence of tridimensional networks in the binary nanocomposites PCL/OMMT and PCL/OMMT/Gr. The good state of dispersion of the hybrids nanofillers (OMMT + Gr) has considerably improved the water vapor permeability and the thermal resistance of the PCL matrix. The dispersability of the nanofillers and their effect on the miscibility were the subject of the last part devoted to the PLA/PCL immiscible blend. Very interesting viscoelastic properties were obtained after the incorporation of the OMMT/Gr mixtures, indicating the existence of good level of distribution of nanofillers in the PLA/PCL matrix. The synergy between the OMMT and epoxy functionalized graphene led to the best improvement in term of barrier properties, thermal stability and compatibility of the matrix.

Ph.D. (Chemistry) / Please refer to full text to view abstract

Ph.D. (Chemistry) / Alchornea species (Euphorbiaceae) have been used in traditional medicine across Africa and are well known to display broad spectrum biological activities including anti‐microbial, antiinflammatory and anti‐cancer activities. This project is aimed at discovering bioactive compounds for anti‐microbial and anti‐cancer therapy from plants of the Alchornea species and developing suitable nanocarrier drug delivery systems (DDS) as drug or compound transporters using gold nanoparticles and natural polymers. The plant material (roots, stems and leaves) was collected in bulk from an uncultivated farmland of the Elounden Mount, in the Yaoundé central region of Cameroon. The extracts were prepared using solvents of varying polarity in order to extract a wide range of phytochemicals. The extracts of A. cordifolia, A. floribunda and A. laxiflora as well as those isolated compounds that were sufficiently pure, were screened for antibacterial activity against four Gram‐positive bacteria (Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus and S. saprophyticus) and four Gram‐negative bacteria (Escherichia coli, Klebsiella pneumonia, Moraxella catarrhalis and Proteus mirabilis), as well as antimycobacterial activity (Mycobacterium aurum and M. smegmatis). The anti‐cancer properties were similarly tested against SNO oesophageal cancer, breast cancer (MDA‐MB‐231 and MCF‐7), and leukemia HL‐60 cell lines. The antimicrobial activities were evaluated using the micro‐dilution assay while the anticancer activity was evaluated by means of cell viability (MTT assay, Alamar blue, trypan blue and an ATP assays). The isolation of compounds and synthesis of derivatives were performed by exhaustive chromatographic techniques and suitable organic reactions. The structures of the compounds were determined by means of spectroscopic methods (FT‐IR, MS, 1D and 2D NMR). Three compounds (AC3.1, AC2.4 and 3HB) were used to synthesize DDS and were characterized using UV‐Vis, FT‐IR, TEM, SEM, XRD, EDS, DLS and zeta potential.

PhD. (Chemistry) / Well-defined palladium and platinum nanoparticles were synthesized by two template methods, namely dendrimer template and reverse microemulsions. For dendrimer template, three dendrimers, generation 4, 5, and 6 hydroxyl terminated poly(amidoamine) dendrimers (PAMAM), G4-OH, G5-OH, and G6-OH, were used as stabilizing agent, with PdCl4 2- or PtCl4 2- metal ions to dendrimer ratio of 40, 80, and 160, respectively. For reverse microemulsions, we employed water/AOT surfactant/isooctane system with water to surfactant ratios (ω0) of 5, 10, and 13, capped with thiol, to produce Pd and Pt nanoparticles. A total of twelve catalysts were characterized by techniques such as UV-Vis spectroscopy, TEM, EDX, and p-XRD. In the dendrimer template method, the synthesis of Pd and Pt nanoparticles in lower concentrations produced smaller sizes with narrower size distributions (2.02 ± 0.45 ~ 2.35 ± 0.58 nm Pd nanoparticles, 1.90 ± 0.44 nm ~ 2.48 ± 0.60 nm Pt nanoparticles) compared to those in higher concentrations (2.74 ± 0.44 ~ 3.32 ± 0.86 nm Pd nanoparticles, 2.81 ± 0.70 nm ~ 3.03 ± 0.47 nm Pt nanoparticles). In the case of thiol-capped Pd and Pt nanoparticles by reverse microemulsions, the range of average particle sizes were 3.47 - 7.51 nm and 3.51 - 4.23 nm for Pd and Pt nanoparticles, respectively. This indicated that a wider size regime was obtained by the reverse microemulsion method as compared to the dendrimer template method. Overall, smaller sizes with narrower size distributions were achieved by using the dendrimer-templated synthetic method rather than reverse microemulsions for both Pd and Pt nanoparticles.