Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-08-10Bitstream added on 2014-06-13T20:33:16Z : No. of bitstreams: 1 pereira_ds_me_ilha.pdf: 5937510 bytes, checksum: c32d623d3e0fbcd57127c9f447e87b2e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Resinas epoxídicas são uma das mais importantes classes de polímeros termorrígidos usados para aplicações estruturais e como adesivos. Entretanto, os problemas em aplicações de resinas epoxídicas na engenharia incluem a baixa resistência à propagação de trincas devido a sua fragilidade. Para superar esta fragilidade, muitas vezes, dentre os aditivos em formulações multicomponentes de resinas epoxídicas, é utilizado um componente para aumentar a resistência, tais como enchimentos, oligosilsesquioxanos poliédricos (POSS), dendrímeros, etc. POSS (RSiO1,5)n podem ser incorporados em polímeros termorrígidos para melhoramento de suas propriedades térmicas e mecânicas. O uso de POSS nanoestruturados na preparação de polímeros orgânicos pode levar a materiais nanocompósitos. Neste trabalho, um POSS contendo oito grupos ésteres por molécula (MDPS) foi incorporado a uma matriz de polímeros termorrígidos epoxídicos DGEBA/TETA para melhorar suas propriedades mecânicas. Através de ensaios mecânicos foi observado um aumento de aproximadamente 90% (formulação 0,67/5) na resistência a fratura (K1C) com um leve decréscimo no modulo de Young (E). Os valores de Tg, verificados por DMTA mostraram pequeno decréscimo nas composições modificadas. As análises termogravimétricas mostraram que a adição de silsesquioxano não influenciou na estabilidade térmica do material. A cinética de cura foi analisada pelo método de Ozawa. As possíveis e prováveis causas deste significante reforço podem ser atribuídas à formação de uma segunda fase, à miscibilidade residual dos grupos ésteres com a matriz epoxídicas e às interações interfaciais entre a matriz epoxídicas e os cubos de silsesquioxanos devido as suas dimensões nanométricas. / Epoxy resins are one of the most important classes of thermosetting polymers used for structural and adhesive applications. However, the current problems in engineering applications of epoxy thermosets include the poor resistance to the crack propagation because they are brittle. To overcome brittleness, among other additives of the multicomponented formulation of the epoxy resin, a toughening agent is often used, such as fillers, polyhedral oligosilsesquioxanes (POSS), dendrimers, etc. POSS, (RSiO1.5)n, can be incorporated into thermosetting polymers to improve their thermal and mechanical properties. The use of such nanosized POSS in the preparation of an organic polymer can lead to a nanocomposite materials. In this work, a POSS containing eight ester groups per molecule (MDPS) was incorporated to an epoxy matrix of DGEBA/TETA thermosetting polymers to improve their mechanical properties. Through the mechanical tests an increase of about 90% (formulation 0,67/5) was observed in the fracture toughness (K1C) with a little decreasing in the module of Young (E). The Tg values verified by DMTA showed smaller values for the compositions with the modifier. The thermogravimetric analyses showed that the addition of the silsesquioxane ester did not influence on the thermal stability of the material. The cure kinetics was analyzed by Ozawa's method. The probable and possible causes of this significant reinforcement can be attributed to the formation of a second inorganic phase, residual miscibility of the ester groups with the epoxy matrix and to interfacial interactions between the epoxy matrix and silsesquioxanes cubes due their nanometric dimensions.

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Block copolymer (BCP) phase segregation and self-assembly into two or more distinct domains are primarily dictated by two parameters: the block volume fraction, f, and the product of the segment-segment interaction parameter and the length of polymer chain, XN. The volume fraction determines a block copolymer's phase segregated morphology, whereas XN dictates its overall segregation strength, or phase stability. In order to achieve smaller domain sizes, the interaction parameter must be increased to compensate for the decrease in chain length. In the melt, PEO-b-PPO-b-PEO (Pluronic) triblock copolymer surfactants do not phase segregate primarily due to their low molecular weights and insufficient segregation strength, or low XN. Strong hydrogen bonding and selective interactions of PEO chains with homopolymers capable of hydrogen bonding, such as poly(acrylic acid) were shown to increase the effective segregation strength of the blend. Small angle X-ray scattering demonstrated highly ordered sub-10 nm domains resulting from phase segregation of the blends. The strong hydrogen bonding interaction between PEO and H-bonding homopolymers was also utilized to incorporate polyhedral oligomeric silsesquioxanes (POSS) into silicate films. In order to improve the compatibility between hydrophobic POSS with hydrophilic Pluronic copolymers, POSS-decorated acrylate monomer was copolymerized with acrylic acid. This eliminated the macrophase segregation between the BCP templates and POSS molecules. The inclusion of POSS is shown to increase the mechanical performance of the low-k films. A supercritical CO2 synthesis route enables the transport of silica precursors into the polymer blends. An increase of hardness of up to 1.8 GPa at k = 2.4 and 1.2 GPa for k = 2.1 was observed for these mesoporous organosilicate films. Finally, this work has also focused on the formation of ordered domains of the Pluronic surfactants into a ternary solvent system consisting of two liquid solvents and compressed CO2. Compressed CO2 can influence the compatibility of liquid solvents, inducing phase separation or phase mixing. CO2-induced phase separation of acetone and water and phase mixing of tetradecane and methanol were studied for the formation and breaking of nanoscale domains in the presence of Pluronic surfactants. Long-range ordered structures were observed using small angle neutron scattering.

The work presented in this thesis can be divided into two research areas. First, two sets of organic-inorganic hybrid nanocomposites containing phenolic resin/trisilanolphenyl-POSS and phenolic resin/octa(aminophenyl)-T8-POSS nanocomposites were synthesized and the morphology and properties were investigated. Octa(aminophenyl)-T8-polyhedral silsesquioxane is an octafunctional-T8-POSS containing eight aniline-like amino groups, one on each corner silicon atom. It was synthesized in our laboratory by an improved two-step reaction sequence; nitration (HNO3) and reduction (HCOOH/Et3N). Varying amounts of POSS were codissolved with a resole phenolic resin in organic solvent. This was followed by solvent removal and thermal curing. Intermolecular interactions in these nanocomposites were probed by FT-IR. The micro-morphology and aggregation state of POSS were investigated using SEM, TEM, and WAXD studies. The thermal and mechanical properties and thermal stabilities of these composites were investigated by DMTA, DSC, and TGA. Second, two types of carbon-covered mono- and bimetallic (Sn, and Sn/Sb alloy) nanorods for use as anode materials in lithium ion batteries were synthesized by a thermal chemical vapor deposition method. Commercial antimony and tin oxide (Sb3O4/SnO2) nanopowders and added tin (IV) oxide (SnO2) nanoparticles (~19 nm) were used as the precursors for the growth of bimetallic Sn/Sb alloy and monometallic Sn nanorods, respectively. In addition, the shape of the products recovered were different when different hydrocarbon gas flow rates were used for growing intermetallic nanorods in carbon templates. Acetylene and methane were the gases tried. The morphologies and structures of the intermetallic nanorods in carbon templates were investigated using SEM and TEM and proved by X-EDS, XRD, and XPS studies.

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Over the past two decades one class of oligomers, polyhedral oligomeric silsesquioxanes (POSS), has attracted considerable attention because of their unique hybrid organic/inorganic molecular structures and nanoscopic sizes. While surface and interfacial properties may play a key role in many potential POSS applications, relatively little is actually known about the surface properties of POSS. This dissertation provides studies of the interfacial aspects of both POSS molecules and POSS/polymer blends at the air/water interface (A/W) through surface pressure-area per molecule (π-<i>A</i>) isotherm, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) studies. Results for POSS Langmuir thin films at A/W show that trisilanol-POSS derivatives are a new class of amphiphiles, that exhibit multiple phase transitions in going from traditional 2D Langmuir monolayers (1 POSS molecule thick) to various 3D multilayer films upon compression. With small length/diameter ratios and bulky shapes, the monolayer phase behavior and packing states of different POSS are simpler than the traditional rod-like lipids. Meanwhile trisilanol-POSS derivatives have very different collapse behavior and multilayer organization showing strong substituent effects even though they have similar molecular sizes. While trisilanolisobutyl-POSS (TiBuP) monolayers undergo collapse around π ≈ 18 mNm⁻¹ and form various ordered or disordered solid-like 3D aggregates at different compression rates, trisilanolcyclohexyl-POSS (TCyP) monolayers collapse into trilayers via instantaneous nucleation with hemispherical edge growth around π ≈ 3.7 mNm⁻¹. ISR results reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms. Further symmetric compression after trilayer formation induces TCyP thin films to self-assemble into highly ordered crystalline-like hydrophobic multilayers (≈8 POSS molecule thick) with unique rod-like morphologies, which are dramatically different from –collapsed– morphologies seen in other systems. By treating POSS derivatives as ideal nanofiller for studying confinement effects on filled polymer systems, amphiphilic poly(dimethylsiloxane) (PDMS) derivatives with different polar functional groups are studied as blends with TiBuP and octaisobutyl-POSS at A/W to resolve one of the key challenges for current nanocomposite applications: How to control nanofiller dispersion in polymer matrices? The results in this dissertation reveal that introducing polar groups into polymeric matrix polymers is a good way to control dispersion. / Ph. D.

The development of organic-inorganic hybrid materials is of great interest in thermoelectrics for its potential to combine the desirable characteristics of both classes of materials. Thermoelectric materials must combine low thermal conductivity with high electrical conductivity, but in most materials, thermal and electrical conductivity are closely related and positively correlated. By combining the low thermal conductivity, flexibility, facile processing, and low cost of organic components with the high electrical conductivity and stability of inorganic components, materials with beneficial thermoelectric properties may be realized. Here, we describe the synthesis and characterization of anthracene-containing organic-inorganic hybrid materials for thermoelectric purposes. Specifically, POSS-ANT was synthesized when aminopropylisobutyl-POSS was functionalized with a single anthracene unit via DCC-mediated amide formation. Acrylate-POSS was functionalized with multiple anthracene units in a Heck coupling reaction to synthesize System 1. System 2 was developed through a two-step synthetic process. In the first reaction, (3- acryloxypropyl)methyl dimethyoxy silane was functionalized with anthracene at the 9- position through a Heck coupling reaction. The second reaction was a base-catalyzed solgel process to form polymeric nanoparticles. Finally, System 3 was synthesized through a similar process to System 2, though polymers formed in the initial step. The System 3 precursor was to be developed through a potassium carbonate-catalyzed ether synthesis from 3-(bromopropyl)trimethoxysilane and 9-anthracene methanol, followed by a basecatalyzed sol-gel process to form nanoparticles. The precursor was never isolated because of premature polymerization during the precursor synthesis step, and polymeric nanoparticles were obtained for System 3 during the sol-gel process. These materials were characterized by TEM to reveal the nanostructures that formed upon evaporation from solution. Future work will focus on the characterization of thermoelectric parameters and incorporation into thermoelectric devices.

Le projet de thèse a pour but de synthétiser de nouveaux matériaux siliciques à microstructure contrôlée en utilisant des procédés de polycondensation à basse température, et de développer de nouvelles approches de microfabrication 3D à haute résolution par excitation bi-photonique d’une formulation sol-gel. La synthèse de matériaux microstructurés est ici centrée sur le procédé sol-gel, impliquant des réactions d’hydrolyse-polycondensation. Les mtériaux les plus étudiés par ces approches en particulier dans le cadre d’un contrôle de la porosité sont préparés à partir de tetraéthoxide de silicium (TEOS)/ Le matériau est structuré généralement par des agent moléculaires structurants (« templates ») tels que les composés tensioactifs. Ces derniers sont en général éliminés, après condensation des silanols, par traitement thermique ou lavage afin de libérer la porosité et générer la structuration. Cette étape d’élimination des agents structurants est souvent problématique, en particulier au niveau industriel, car elle utilise soit des hautes températures, soit des quantités importantes de solvants. Il y a un enjeu important à développer des approches de microstructuration s’affranchissant de ces agents moléculaires structurants, cela représentant le principal objectif de cette thèse.Deux stratégies sont abordées aux cours de ce travail de recherche. La première implique l’utilisation de précurseurs organosilylés donc la structure moléculaire permet une microstructuration du matériau synthétisé. Cette partie explore l’utilisation de précurseurs de la famille des silsesquioxanes et leur transformation vers les matériaux. La deuxième approche propose d’évaluer pour la première fois l’utilisation de l’excitation biphotonique pour contrôler l’étape de condensation sol-gel par modification de pH au point focal d’un laser et ainsi apporter une résolution micrométrique à la structuration du matériau / The main goal of this research was the synthesis of new siliceous materials with controlled microstructures, using low-temperature polycondensation process, and develop the new approach towards 3D microfabrication under two-photon excitation of a sol-gel formulation. Synthesis of microstructured materials is based on the sol-gel process, i.e. hydrolytic polycondensation. Most known siliceous materials with controlled microstructure are synthesized from tetraethoxysilane (TEOS). The materials are generally structured by structuring molecular agents ("templates") such as surfactant compounds, which are then removed by heat treatment or washing with appropriate solvents. This stage of removal of structuring agents is often problematic, particularly at the industrial level, because it uses either high temperatures or large amounts of solvents. Therefore, new methods to obtain materials with controlled porosity without the need to use templates are still being developed. Two strategies are discussed during this research work. First one involved the use of organosilicon precursors with a define structure that at molecular level modify the structure of the final materials. The use of well-defined precursors (silsesquioxanes), in appropriate proportions, allows the control of the porosity of the obtained silica materials. The second approach investigated in this work is the local photo-induced structuration of silicon based pre-hydrolyzed precursors under two-photon excitation allowing high 3D resolution