Anodisation is a surface treatment process, commonly used to form a protective oxide coating on the surface of metals like aluminium. Anodised coatings, being grown out of the base metal have excellent interface strength but are porous and brittle. Porosity of the coating reduces the hardness and the brittle nature of the oxide induces cracking. In practice, the pores are typically filled with organic dye and sealed. Under certain controlled electrochemical conditions, anodisation results in a highly ordered hexagonal porous structure in pure aluminium. In this work, we explore the possibility of using this ordered porous alumina to form a novel metal nanocomposite as a tribological coating. By optimizing the nonporous structure and tuning the electrodeposition process, we uniformly filled the ordered pores with copper. We have measured the hardness of the resulting ordered and aligned nanocomposite. We explore the possibility of using this composite coating for tribological applications by carrying out some preliminary reciprocating wear test. Ordered porous alumina layer is formed by a two-step anodisation process. By optimizing the anodisation conditions, we control the thickness of the coating and the pore size. The interface of the porous structure and aluminium substrate is defined by a non-conducting dense barrier oxide layer. However, to deposit metal into the pores, a conducting path should be established through the barrier layer. One possibility is to etch out the bottom of the pores at the cost of the interface strength and losing out on the main advantage of anodised coatings. To be able to fill metal without this sacrifice, we utilised the dendritic structure in the barrier layer formed by a step-wise reduction of voltage towards the end of anodisation process. Optimisation of this dendritic structure led to uniform deposition of metal into pores, achieved by pulsed electrodeposition. In pulse lectrodeposition, a positive pulse is applied to remove accumulated charge near to the bottom of pores, followed by a negative pulse to deposit metal and a delay to allow diffusion of ions. By optimising the pulse shape and duration, we have achieved uniform growth of metal into pores. Further, monitoring the deposition current helped us to identify and control different phases of growth of the nanowire. The properties of the porous alumina and the nanocomposite were measured by nanoindentation. The deformation characteristics were obtained by observing the indents in a FE-SEM. We find that dendritic modification of interface has very little effect on the hardness of the porous alumina layer. We also found that the porous alumina deformed either by compaction or by forming circumferential and radial cracks. When copper is filled in the nano pores, the hardness increased by 50% and no circumferential cracks were found up to the load of 10 mN for a film thickness of about 1 µm. Coefficient of friction of the coating reciprocated against steel in dry condition is found to be around 0.4. Minimal wear was observed from the SEM images of wear track. In summary, a novel nanocomposite coating with ordered porous alumina as matrix embedded with aligned metal nano rods has been developed. This was achieved by optimally modifying the barrier layer without sacrificing the interfacial strength. Uniform coating has been achieved over an area of 10 mm x 10 mm. The coating is found to have high hardness and high wear resistance.

The uniform dispersion of the nano fillers without agglomeration in a polymeric matrix is widely adapted for the purpose of mechanical properties enhancement. In the context to biomedical applications, the type and amount of nanoparticles can potentially influence the biocompatibility. In order to address these issues, High Density Polyethylene (HDPE) based composites reinforced with graphene oxide (GO) were prepared by melt mixing followed by compression moulding. In an attempt to tailor the dispersion and to improve the interfacial adhesion, polyethylene (PE) was immobilized onto GO sheets by nucleophilic addition-elimination reaction. A good combination of yield strength (ca. 20 MPa), elastic modulus (ca. 600 MPa) and an outstanding elongation at failure (ca. 70 %) were recorded with 3 wt % polyethylene grafted graphene oxide (PE-g-GO) reinforced HDPE composites. Considering the relevance of protein adsorption as a biophysical precursor to cell adhesion, the protein adsorption isotherms of bovine serum albumin (BSA) were determined to realize three times higher equilibrium constant (Keq) for PE-g-GO reinforced HDPE composites as compared to GO reinforced composites. In order to assess the cytocompatibility, osteoblast cells (MC3T3) were grown on HDPE/GO and HDPE/PE-g-GO composites, in vitro. The statistically significant increase in metabolically active cell was observed, irrespective of the substrate composition. Such observation indicated that HDPE with GO or PE-g-GO addition (upto 3 wt %) can be used as cell growth substrate. The extensive proliferation of cells with oriented growth pattern also supported the fact that tailored GO addition can support cellular functionality, in vitro. Taken together, the experimental results suggest that the PE-g-GO in HDPE can effectively be utilized to enhance both mechanical and cytocompatibility properties and can further be explored for potential biomedical applications.

The research goal of this work was dedicated to improvement of the properties and enhancement of the application potential of commodity polymer based on polyolefins by choosing different synthesis routes to create new structures and materials. More precisely, the presented study explores different aspects of metallocene and post-metallocene catalyzed olefin polymerization leading to synthesis of novel copolymers and nanocomposites. The first part of this thesis deals with controlled polymerization of α-olefins catalyzed by post-metallocenes. Bis(phenoxyamine) zirconium complexes with [ONNO]-type ligands bearing cumyl (bPA-c) and 1-adamantyl (bPA-a) ortho-substituents were applied. For the polymerization catalyzed by bPA catalyst quasi-living kinetic character is proposed. The bPA catalyst was applied for synthesis of block copolymers by employing the strategy of sequential monomer addition. The blocky structure of the copolymer was successfully achieved and confirmed by NMR techniques. Moreover, the monomodal distribution of molar mass in SEC chromatogram confirmed the absence of homopolymers. In the second part of the work new defined comb-like copolymers (CLC) having a poly(10-undecene-1-ol) (PUol) backbone and densely grafted poly(ε-caprolactone) (PCL) side chains are presented. These copolymers were synthesized in two steps by means of metallocene polymerization followed by ring opening polymerization. Copolymers with varied and adjustable graft length (PCL segments) were synthesized. It was proved that the melting and crystallization temperatures of the CLC correlate with the PCL side chain length, i.e. longer chains result in higher Tm and Tc,o values. The melting enthalpy was found to be asymptotically dependent on the length of PCL side chains. The bulk morphology of the comb-like copolymers is proposed to be lamellar as judged from the TEM micrographs. The third part of the thesis is focused on the synthesis of polypropylene nanocomposites via in situ polymerization. Thereby, organomodified aluminumphosphate with kanemite-type layered structure (AlPO-kan) has been used as novel filler. Melt compounding composites were prepared for comparison purposes to evaluate the influence of in situ synthesis on the dispersion quality of the filler in polymer matrix. Melt compounding of neat AlPO-kan with PP did not lead to formation of nanocomposites. TEM images show macro-composites with the lamellar solid remaining agglomerated. On the contrary, in situ polymerization of propene yielded materials with exfoliated nanocomposite morphology. In XRD, diffractions of the AlPO-kan pilling of layers are not detectable. It can be concluded that the primary existing layers are delaminated. Very fine distribution of the filler in the polypropylene matrix has been impressively demonstrated by TEM.

La mesure du taux de CO2 est un besoin relativement récent. Les travaux sur l'utilisation de nouveaux matériaux pour la réalisation de capteurs de gaz, efficaces et peu chers, suscitent des intérêts scientifique et technologique croissants. L'objectif de ces travaux de thèse est l'élaboration et la caractérisation de nouvelles couches sensibles obtenues par pulvérisation cathodique radiofréquence pour la réalisation de capteurs de CO2. Les films minces ont été déposés à partir d'une cible céramique de CuO, dans diverses conditions de dépôt, en variant la pression d'argon dans l'enceinte et la puissance RF appliquée. Dans un premier temps, nous avons caractérisé la structure et la microstructure des films bruts et recuits sous air par DRX, MEB, AFM et spectroscopie Raman. Nous avons également étudié les propriétés physiques des films minces ainsi que leur surface accessible par adsorption de gaz krypton (méthode de Brunauer, Emmett et Teller). Le traitement thermique à 450°C n'affecte pas la structure cristalline des couches, en revanche il tend à faire chuter fortement la surface accessible entre les colonnes. Après l'optimisation des paramètres de fonctionnement de la cellule de mesure, nous avons caractérisé les performances des films de CuO pour la détection du CO2. La meilleure réponse (?R/R=51 %) a été obtenue pour une couche élaborée à 2 Pa avec une puissance RF de 30W. De plus, la température optimale de mesure est relativement basse (T= 250°C). Le contrôle de la microstructure et plus particulièrement de la taille des grains s'est avéré être le paramètre principal qui impacte la réponse sous CO2. Les meilleurs résultats ont été obtenus avec des tailles de grains proches d'une vingtaine de nanomètres de diamètre. Une bonne modélisation de la réponse électrique en fonction de la taille des grains a pu être réalisée en prenant en compte un circuit électrique équivalent comportant une zone enrichie en porteur de type trous à la surface des grains et dont l'épaisseur est de l'ordre de la longueur de Debye. / The measure of the rate of CO2 is a recent need. The works on the use of new materials for the conception of gas sensors based semiconductor oxides, effective and not expensive; arouse a huge interest in our society. The objective of this thesis is the elaboration and the characterization of new sensitive layers obtained by RF sputtering for the realization of the sensors of CO2. Thin films were deposited using two targets: CuFeO2 and CuO, under three conditions by varying argon pressure and RF power. First of all, the structure and the microstructure were studied for the as-deposited samples. Surface investigations carried out by Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Raman spectroscopy, BET measurements and MEB-FEG images have shown a strong influence of deposition technique parameters on film surface topography and morphology. In a second step, the thin films were annealed in air in order to oxidize the phase. For the composite CuO/CuFe2O4, Glow discharge optical emission spectrometry technique showed a structure in two layers stacked on top of each other for the thinner films. For the cupric films, no changes on both structure and microstructure have been revealed. Our films have then been evaluated for CO2 detection. The sensitive layers with different thicknesses were sensitive to 5000 ppm of CO2. The deposition parameters are optimized to obtain microstructure features which can enhance the sensitivity of the thin films as gas sensors. Best response was obtained for a cupric sample deposited in P2 30W conditions and was close to 50% at T = 250°C. We have demonstrates that cupric oxide alone can detect the CO2 gas and that the growth conditions determine the film surface characteristics. The gas sensing characteristics of these films are strongly influenced by both surface morphology and microstructure.

Developing next generation secondary batteries has attracted much attention in recent years due to the increasing demand of high energy and high power density energy storage for portable electronics, electric vehicles and renewable sources of energy. This dissertation investigates sulfur based advanced electrode materials in Lithium/Sodium batteries. The electrochemical performances of the electrode materials have been enhanced due to their unique nano structures as well as the formation of novel composites. First, a nitrogen-doped graphene nanosheets/sulfur (NGNSs/S) composite was synthesized via a facile chemical reaction deposition. In this composite, NGNSs were employed as a conductive host to entrap S/polysulfides in the cathode part. The NGNSs/S composite delivered an initial discharge capacity of 856.7 mAh g-1 and a reversible capacity of 319.3 mAh g-1 at 0.1C with good recoverable rate capability. Second, NGNS/S nanocomposites, synthesized using chemical reaction-deposition method and low temperature heat treatment, were further studied as active cathode materials for room temperature Na-S batteries. Both high loading composite with 86% gamma-S8 and low loading composite with 25% gamma-S8 have been electrochemically evaluated and compared with both NGNS and S control electrodes. It was found that low loading NGNS/S composite exhibited better electrochemical performance with specific capacity of 110 and 48 mAh g-1 at 0.1C at the 1st and 300th cycle, respectively. The Coulombic efficiency of 100% was obtained at the 300th cycle. Third, high purity rock-salt (RS), zinc-blende (ZB) and wurtzite (WZ) MnS nanocrystals with different morphologies were successfully synthesized via a facile solvothermal method. RS-, ZB- and WZ-MnS electrodes showed the capacities of 232.5 mAh g-1, 287.9 mAh g-1 and 79.8 mAh g-1 at the 600th cycle, respectively. ZB-MnS displayed the best performance in terms of specific capacity and cyclability. Interestingly, MnS electrodes exhibited an unusual phenomenon of capacity increase upon cycling which was ascribed to the decreased cell resistance and enhanced interfacial charge storage. In summary, this dissertation provides investigation of sulfur based electrode materials with sulfur/N-doped graphene composites and MnS nanocrystals. Their electrochemical performances have been evaluated and discussed. The understanding of their reaction mechanisms and electrochemical enhancement could make progress on development of secondary batteries.

Hypersonic aerospace vehicles are severely limited by the lack of adequate high temperature materials that can withstand the harsh hypersonic environment. Tantalum carbide (TaC), with a melting point of 3880°C, is an ultrahigh temperature ceramic (UHTC) with potential applications such as scramjet engines, leading edges, and zero erosion nozzles. However, consolidation of TaC to a dense structure and its low fracture toughness are major challenges that make it currently unviable for hypersonic applications. In this study, Graphene NanoPlatelets (GNP) reinforced TaC composites are synthesized by spark plasma sintering (SPS) at extreme conditions of 1850˚C and 80-100 MPa. The addition of GNP improves densification and enhances fracture toughness of TaC by up to ~100% through mechanisms such as GNP bending, sliding, pull-out, grain wrapping, crack bridging, and crack deflection. Also, TaC-GNP composites display improved oxidation behavior over TaC when exposed to a high temperature plasma flow exceeding 2500 ˚C.

Le développement de procédé évoluant à la pression atmosphérique représente un enjeu majeur dans le dépôt de couches minces nanocomposites. Parmi ces procédés, les Décharges à Barrières Diélectriques présentent l'avantage d'être un procédé vert sans effluent gazeux, pouvant facilement être intégrées dans une chaine de production industrielle. L'approche choisie pour la réalisation de couches minces nanocomposites repose sur l'injection sous forme d'aérosol d'une suspension colloïdale dans la DBD. Les nanoparticules semi-conductrices de TiO2 sont choisies et mise en suspension dans un alcool polymérisable tel que l'isopropanol. L’objectif de ce travail est de contrôler le transport des nanoparticules et la croissance de la matrice dans la DBD en vue de réaliser une couche mince nanocomposite.Différentes méthodes de formation de l'aérosol et de filtration sont évaluées, ainsi que différents gaz vecteur (Ar, N2). Dans tous les cas considérés, la décharge est filamentaire.L'estimation des valeurs des différentes forces s'exerçant sur une nanoparticule dans une DBD confortée par un modèle numérique à permis d'orienter les expérimentations. Il est ainsi possible, à partir des paramètres permettant de générer le plasma, d'influencer le dépôt des nanoparticules et la croissance de la matrice. Les dépôts obtenus sont analysés ex situ par microscopie électronique à balayage, spectroscopie infrarouge, Raman et à rayon X et in situ avec la diffusion laser.Dans le régime filamentaire considéré, nous montrons que le flux de gaz et la fréquence de la tension joue des rôles prépondérants sur le dépôt des couches minces nanocomposites. Cette étude a permis de mettre en évidence qu’une simple fréquence n’est pas suffisante pour déposer la couche mince nanocomposite. Cependant l’utilisation d’une double fréquence semble être la meilleure approche pour séparer le transport des nanoparticules de celui de la croissance de la matrice. / Development of an atmospheric pressure process presents a major concern in the deposition of nanocomposites thin films. Among these processes, Dielectrics Barrier Discharges takes advantages to be green processes without gas effluent, which can be easily integrate in an industrial line production. The chosen approach for the nanocomposite thin film deposition is based on the injection of an aerosol of a colloidal suspension in the DBD. Semi-conductive TiO2 nanoparticles are chosen and put in suspension in a polymerizable alcohol as isopropanol. The objective of the present work is to control the transport of the nanoparticles as well as the matrix growth in the DBD in order to realize the nanocomposites thin film Different methods of the aerosol formation and filtration are evaluated, as well as the carrier gas (Ar, N2). In each case considered, the discharge works in filamentary. Estimating values of the different forces acting on the nanoparticles in a DBD comforted by a numerical model allowed to guide the experimentations. Thanks to the parameter which generated the plasma, it is possible to influence the nanoparticles deposition and the matrix growth. Depositions are ex situ analyzed by scanning electron microscopy, Infra-red, Raman, and X-ray spectroscopy and in situ by laser scattering. In the filamentary regime considered, we show that the gas flow rate and the frequency of the voltage play a dominant role on the deposition of nanocomposites thin films. This study allowed to highlight that a simple frequency is not enough to deposit the nanocomposite thin film. However, the use of a double frequencies seems to be the best way to separate the nanoparticles transport to the surface from that of the matrix growth.

No description available.

One of the most significant issues in nanocomposite performance is improving the dispersion of carbon nanotubes (CNTs) in thermosetting or thermoplastic polymers in order to gain good mechanical properties. Several studies have investigated the fabrication of nanocomposites based on carbon nanotubes and analysed properties, but there is still insufficient data on their structure-property relationships. This thesis has investigated the central importance of stress transfer Raman studies in epoxy composites reinforced with single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs) to elucidate the reinforcing ability of the CNTs in an epoxy matrix. This project was undertaken to synthesise and characterize MWCNTs and determine the effect of different weight fractions of untreated MWCNTs on the stress transfer efficiency at the MWCNTS / epoxy interface and on the stiffness of the thermomechanical properties of the MWCNTS / epoxy composites. It was undertaken to assess the stress transfer efficiency at the CNT / epoxy interface and at the inter-walls of the CNTs with tensile deformation and with cyclic loading.Optimized conditions of the injection chemical vapour deposition method (CVD), such as long injection times were applied to produce MWCNTs with a high yield, high aspect ratio and well-defined G' Raman peak. The morphology and size of CNTs were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) while their thermal stability was examined by Thermogravimetric analysis (TGA). Both Raman spectroscopy and mechanical testing (static and dynamic) were utilized in this study. The Raman spectroscopy research consisted of following the G'-band frequency and linewidth as well as the intensity of radial breathing modes (RBMs) during tensile deformation. The stress-induced Raman shifts in the nanocomposites have been shown to be controlled by the number of carbon nanolayers. A theory has been developed to determine and simulate the stress transfer efficiency parameter, (k_i) for MWCNTs. Tensile tests and dynamic mechanical testing were used to assess the mechanical properties of the nanocomposites.The most obvious finding to be drawn from the present study is that the reinforcement of the epoxy resin with different loadings of MWCNTs is useful, but the best reinforcement was at low loadings of MWCNTs. One of the more significant findings to emerge from this study is that (k_i) between the inner walls of the DWCNTs and MWCNTs are quite similar (~0.7), which suggest that (k_i) may be similar for all CVD MWCNTs and DWCNTs. The second major finding was that there were RBM intensity variations for the SWCNTs and DWCNTs in the hot-cured epoxy composites and that for the DWCNTs both the inner and outer nanotube walls are stressed during deformation

Orientadores: Júlio Roberto Bartoli, Elizabeth Grillo Fernandes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T08:51:19Z (GMT). No. of bitstreams: 1 Cecci_RicardoRodrigoRamos_M.pdf: 4182332 bytes, checksum: 4424cc557c439a1602d15a95921a2b25 (MD5) Previous issue date: 2013 / Resumo: Nanotubos de carbono (NTCs) apresentam características interessantes para aplicações em eletrodos transparentes. Quando dispersos em escala nanométrica são transparentes ao espectro da luz visível e são capazes de conduzir eletricidade após atingirem percolação em matrizes poliméricas isolantes. Neste trabalho, é descrito o uso de nanotubos de carbono de camadas múltiplas (NTCMs) na produção de filmes poliméricos flexíveis transparentes e condutores como alternativa ao uso do óxido de índio dopado com estanho (ITO) em células solares orgânicas. Os nanotubos foram dispersos e purificados em solução aquosa de dodecil sulfato de sódio (SDS) pelos processos de sonicação e centrifugação, e a dispersão monitorada por espectroscopia UV-Vis e potencial ?. Os nanocompósitos foram produzidos via polimerização in situ do monômero metacrilato de metila (MMA) na presença de 0 a 1% p/p NTCs e os filmes depositados através da técnica de revestimento por rotação a alta velocidade (spin coating). A reação de polimerização foi acompanhada pela calorimetria exploratória diferencial (DSC). Verificou-se que na presença de NTCs, a taxa de conversão do monômero é acelerada. A cinética de degradação térmica foi avaliada pelo método de Broido utilizando a análise termogravimétrica (TGA). Foi observado que os NTCs aumentam a estabilidade térmica do PMMA, retardando a degradação por despolimerização. Estudos por espectroscopia FT-IR mostraram uma banda de absorção em 1601 cm-1, (C=C), a qual não é característica do PMMA, indicando que os NTCs participam da polimerização do PMMA. Para concentrações de até 1% p/p de NTCs, os filmes PMMA/NTC apresentaram excelentes propriedades ópticas. Ou seja, baixo coeficiente de absorção, na ordem de 103 cm-1, altos valores de gap óptico (Eopt), entre 3,2 e 4,14 eV, e alta transparência por todo espectro visível, entre 88 e 93%. Nas mesmas concentrações, foi observada uma diminuição substancial na resistividade elétrica dos filmes em 8 ordens de grandeza (de 1016 para 108 ?/quadrado), comparados ao filme de PMMA puro. Entretanto, a faixa de resistividade alcançada ainda é típica de materiais isolantes. Estudos de otimização poderiam originar filmes PMMA/NTC como uma alternativa promissora para ITO em OPVs / Abstract: Carbon nanotubes (CNTs) have interesting features for applications in transparent electrodes. When dispersed at the nanoscale, they become transparent within the visible range and are able to conduct electricity after reaching the percolation threshold in an insulating polymer matrix. In this work, the use of multi-walled carbon nanotubes (MWCNTs) is described for the production of flexible transparent conducting polymer films as an alternative to the use of indium-tin oxide (ITO) in organic solar cells. The nanotubes were dispersed and purified in an aqueous solution of sodium dodecyl sulfate (SDS) by the process of sonication and centrifugation, and the dispersion monitored by UV-Vis spectroscopy and ? potential. The nanocomposites were produced via in situ polymerization of the monomer methyl methacrylate (MMA) in the presence of 0 to 1 %wt. of CNTs. The films were deposited by the spin-coating technique. The polymerization reaction was monitored by differential scanning calorimetry (DSC). It was found that in the presence of CNTs, the conversion rate of the monomer is accelerated. The kinetics of thermal degradation was measured according to the Broido's method by using thermogravimetric analysis (TGA). It was observed that CNTs increase the thermal stability of PMMA, slowing degradation by depolymerization. FT-IR data showed an absorption band at 1601 cm-1 (C = C), which is not characteristic of PMMA, indicating that the CNTs takes place in the polymerization of PMMA. For concentrations up to 1wt% of CNTs, the PMMA/CNT films had excellent optical properties, i.e., a low absorption coefficient in the order of 103 cm-1, wide optical gap (Eopt) between 3.2 and 4.14 eV, and high transparency within the whole visible range, between 88 and 93%. In the same concentrations, the electrical resistivity of the films dropped by 8 orders of magnitude (from 1016 to 108 ?/sqr), compared to the pure PMMA film. Even though this electrical resistivity value is typical of insulating materials, further optimization studies could provide PMMA/CNT films as a promising alternative to ITO in OPV / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química