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No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Ana Paula Jardim Roquete - AVALIAÇÃO DAS PROPRIEDADES CAPACITIVAS DE RECOBRIMENTOS DE SOL-GEL APLICADOS SOBRE ALUMÍNIO ANODIZADO (1).pdf: 2361567 bytes, checksum: 81ac2b44fc68ae0dcd2c6e987e3b4598 (MD5) Previous issue date: 2015-03-27 / O desenvolvimento da indústria de eletrônicos junto à miniaturização dos seus dispositivos gera uma demanda de novos sistemas de armazenamento de energia, como os capacitores. Na busca por esses novos sistemas, o estudo de materiais para uso como capacitores tem papel fundamental. O presente trabalho tem por objetivo o desenvolvimento de um recobrimento com propriedades capacitivas em liga de alumínio, tendo como pré-tratamento o processo de anodização, o qual devido à rugosidade formada sobre a amostra pode auxiliar na aderência do recobrimento. Os recobrimentos foram produzidos a partir do processo sol-gel, o qual forma recobrimentos finos de forma consideravelmente simples e econômica. As amostras de alumínio, obtidas de latas de refrigerante, foram lixadas, para a retirada de seus recobrimentos interno e externo, após passaram por um tratamento superficial, por meio do processo de anodização, o qual foi realizado em três diferentes tempos (15, 20 e 30 minutos). Este tratamento superficial foi avaliado pela técnica de Polarização Potenciostática (PP), indicando as melhores condições de anodização para a deposição de sol-gel. A capacitância para este tratamento superficial foi avaliada por meio de Espectroscopia de Impedância Eletroquímica (EIE) ao longo de um período de seis dias em solução de NaCl 3% p/v em pH 2,7. Ambas as análises identificaram a anodização de 15 min como a melhor condição para a realização do tratamento. Amostras com e sem anodização foram então recobertas por oito composições diferentes de sol-gel, e a partir das avaliações de capacitância de cada recobrimento por EIE foi determinada a melhor composição para a adição de um novo óxido, o óxido de rutênio (RuO2), com o objetivo de aumentar a capacitância do recobrimento. As amostras com a última composição foram avaliadas por EIE, determinando a capacitância do recobrimento, Cronocoulometria, para identificação do comportamento quanto ao carregamento, Difração de Raios-X (DRX) e Microscopia de Força Atômica (MFA), avaliando a superfície das amostras. Obteve-se com as medidas de EIE uma menor capacitância para as amostras recobertas com o último sol-gel em relação às amostras anodizadas, porém por Cronocoulometria foi possível verificar carregamento e descarregamento da superfície, o que indicou um comportamento dielétrico do sol-gel, pois manteve a carga de carregamento após a imposição de um potencial contrário ao aplicado. As análises de DRX e MFA comprovaram a ação da anodização devido à presença de pseudo-boemita e rugosidade da amostra, e a indicação de uma região amorfa para amostras com sol-gel, as quais apresentaram superfícies mais planas. / The development of the electronics industry with the miniaturization of devices creates a demand for new energy storage systems, such as capacitors. In the search for these new systems, the study of materials for use as capacitors has a fundamental role. This work aims at the development of a coating with capacitive properties on aluminum alloy, using as pretreatment the anodizing process, which roughness formed on the sample can assist in coating adhesion. Coatings were produced from the sol-gel process, which forms thin coatings in a simple and economical way. The aluminum samples obtained from soft drinks cans were sanded for the removal of its internal and external coatings after undergone a surface treatment by means of anodizing process, which was conducted at three different times (15, 20, and 30 minutes). This surface treatment was evaluated by the technique of Pontentiostatic Polarization (PP), indicating the best conditions of anodizing process for the deposition of solgel. The capacitance for this surface treatment was assessed using Electrochemical Impedance Spectroscopy (EIS) over a period of six days in 3,0 % NaCl solution at pH 2.7. Both analyzes identified the anodizing 15 min as the best condition for the treatment. Samples with and without anodization were then coated with eight different sol-gel compositions, and from the capacitance ratings of each coating was determined by EIA the best composition for adding a new oxide, ruthenium oxide (RuO2), in order to increase the capacitance of the coating. Samples with this final composition was evaluated by EIA, determining the capacitance of the coating, chronocoulometry, to identify the behavior and loading, X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM) evaluating the sample surface. EIS measurements indicating a smaller capacitance for samples coated with the sol-gel in relation to the anodized samples, however chronocoulometry was verified by loading and unloading surface, which indicated a dielectric behavior of the sol-gel, cause it kept the charging load on the establishment of a potential opposite to that applied. The analysis of XRD and AFM confirmed the anodizing action due to the presence of pseudo-boehmite and roughness of the sample, and the appointment of an amorphous region for samples with sol-gel, which had more flat surfaces.

In der vorliegenden Arbeit wird die kationische Polymerisation neuer Furanmonomere beschrieben, die zu anorganisch-organischen Nanokompositen führt. Die kationische Polymerisation des Tetrafurfuryloxysilans steht dabei im Vordergrund. Ausgehend von den synthetisierten Kompositen wird die Herstellung von anorganischen Oxiden durch thermische Oxidation und von Kohlenstoffmaterialien durch thermische Behandlung in Schutzgasatmosphäre beschrieben. Die Charakterisierung der Komposite, Oxide und Kohlenstoffmaterialien erfolgt mittels Festkörper-NMR-Spektroskopie, Röntgenbeugung und Elektronenmikroskopie. Das Prinzip der neu entdeckten Zwillingspolymerisation wird vorgestellt und anhand verschiedener Beispiele auf seine weitere Anwendbarkeit zur Synthese anorganisch-organischer Kompositmaterialien überprüft.

Inorganic UV-filters in use today often occur as nanoparticles and have a photocatalytic effect, which can be a problem since they can cause negative health effects. This is why Upsalite®, a mesoporous magnesium carbonate recently has been investigated as a UV-filter. Upsalite® itself is however not suitable as a UV-filter since it mainly protects in the UVC range and hence it needs to be complemented by other substances. The substance studied to functionalize Upsalite® in this thesis is titanium dioxide which is an inorganic UV-filter commonly used in sunscreens. In this work two different sol-gel synthesis routes of titanium dioxide have been investigated as well as a co-synthesis of Upsalite® and titanium dioxide. In the first synthesis route already synthesized Upsalite® was mixed with titanium tetra-isopropoxide and 1-propanol. The second synthesis route was a modified version of synthesis routes described in literature where methanol solvent was used and the pressure was altered by CO2. This route was explored due to its resemblance with the Upsalite® synthesis. Pressure, temperature and amount of water were varied to optimize incorporation of Upsalite® and investigate possibilities for a co-synthesis. Subsequently a co-synthesis of Upsalite® and titanium dioxide was performed that resulted in two amorphous composite materials depending on if water was added in the drying procedure or not. When mixing Upsalite® in the synthesis liquid of titanium dioxide, titanium dioxide seems to be deposited on Upsalite®. It is however difficult to determine whether the pores of Upsalite® have been completely filled or if they have collapsed. The acid catalyst HCl promotes formation to crystalline titanium dioxide but Upsalite® instead prevents it. The limited crystallization of titanium dioxide when synthesized with Upsalite® may be due to confinement in the Upsalite® pores. The UV-blocking properties of the TiO2-Upsalite® without HCl are good with an sun protection factor (SPF) of 27 for a 10 wt% blend in a lotion and an SPF of 7 for the sample with HCl. The modified synthesis route of TiO2 showed that it is possible to perform a sol-gel synthesis with a considerably lower amount of water than found in literature and that alteration of temperature and pressure during the synthesis does not affect the crystallization temperature noteworthy. The materials obtained from the co-synthesis are slightly porous, probably consisting of one or several magnesium titanium oxides and a carbonate phase and showed a transmission cutoff in between Upsalite® and titanium dioxide corresponding to an SPF of 5.

Au cours de cette thèse, plusieurs approches de fonctionnalisation anti-bactérienne passive, de type"bactériostatique" utilisant des espèces hydrophobes, et active (selon un standard ISO), de type"bactéricide" utilisant des nanoparticules d'argent métallique ou des espèces à base d'ammoniumquaternaire, ont été testées sur des tissus textiles. Des solutions liquides ont été élaborées par voie sol-gelet photochimique, en association ou non. Elles ont tout d'abord été caractérisées d'un point de vuephysico-chimique, morphologique et structural, afin d'optimiser leur formulation et les caractéristiquesdes espèces en solution vis-à-vis de différents cahiers des charges industriels. Ce travail d'optimisation aen particulier conduit à des solutions stables permettant leur utilisation reproductible au cours du temps.Les solutions ont ensuite été imprégnées sur des échantillons textiles, par un dispositif simplifié de "padcoating"mis au point au cours de la thèse, afin de tester la fonction anti-bactérienne des textiles traités.Selon la nature des espèces imprégnées, l'optimisation des solutions conduit à une fonctionnalité antibactériennepassive ou active respectant l'aspect visuel du textile et ne dénaturant pas son toucher. Destests de lavage de laboratoire ou de lavage ménager en conditions réelles ont également montré unaccrochage notable des espèces imprégnées sur les textiles. Des options ont finalement été proposées pouraccroître cet accrochage afin de répondre à des conditions de lavage industriel. En conclusion, ce travail met en évidence le potentiel des approches d'élaboration par chimie douce en vue de fonctionnaliser des textiles, en permettant en particulier de proposer des méthodologies originales et simplifiées en adéquation avec des impératifs industriels.

This research focuses on the development of spectroelectrochemical sensor formats based on thin film molecular architectures and electrochemical detection of sol-gel encapsulated macromolecular recognition elements. To achieve this goal, there were two major objectives: 1) to demonstrate and characterize conductive polymer grown electrochemically in porous sol-gel thin films with specific regard to the ability of the polymer to mediate charge transfer between sol-gel encapsulated molecules and the electrode surface, and 2) to develop a means to probe the spectroscopic properties of highly absorbent thin films as a function of applied potential. Toward the first objective, diffusion of a derivatized thiophene monomer into a sol-gel thin film and subsequent electropolymerization at an underlying indium-tin oxide (ITO) surface was found to produce a conductive network of polymer capable of mediating electron transfer from encapsulated redox centers in the bulk of the sol-gel film to the electrode surface. At high levels of polymer loading, emergent, sol-gel templated, polymeric structures are formed which extend from the sol-gel surface into the electrolyte solution and exhibit electrochemical properties of ultramicroelectrode arrays. To achieve the second objective, a polychromatic, electroactive attenuated total internal reflectance (EA-ATR) instrument was developed consisting of an indium-tin oxide (ITO) coated glass internal reflection element (IRE). In addition to a high degree of surface sensitivity relative to transmission geometries, this geometry affords acquisition of absorption anisotropy information, via polarization of the incident beam, to determine the orientation distribution in molecular adlayers. To demonstrate these abilities, the orientational distribution of monolayer and bilayer films of perylene and copper phthalocyanine derivatives, respectively, was determined. Furthermore, it was demonstrated that the EA-ATR could be used in a potential-modulated mode (PM-ATR) to study the kinetics of electro-optical switching in conductive copolymer thin films.

No description available.

Silica nanoparticles are effective fluorophore carriers with high potential in imaging, diagnostics, and therapy. The particles are resistant to drastic change of environmental conditions (pH, temperature etc.) and insulate the dyes so as to protect them from photobleaching. Silica chemistry is also versatile and affords an easy modification of the particle composition and surface to integrate targeting ligands or to integrate other nanoparticles. Regardless of their advantages, there exists a lack of dye diversity in the literature that is connected to a low affinity for potential tools for biology and medicineThis thesis describes the development of an alternative method for the synthesis of fluorescent silica nanoparticles and their modification to incorporate iron oxide and gold. cont/d.

Methyl-functionalized porous silica is of considerable interest as a low dielectric constant film for semiconductor devices. The structural development of these materials appears to affect their gelation behaviors and impact their mechanical properties and shrinkage during processing. 29Si solution NMR was used to follow the structural evolution of MTMS (methyltrimethoxysilane) polymerization to gelation or precipitation, and thus to better understand the species that affect these properties and gelation behaviors. The effects of pH, water concentration, type of solvents, and synthesis procedures (single step acid catalysis and two-step acid/base catalysis) on MTMS polymerization were discussed. The reactivity of silicon species with different connectivity and the extent of cyclization were found to depend appreciably on the pH value of the sol. A kinetic model is presented to treat the reactivity of both silicon species involved in condensations separately based on the inductive and steric effects of these silicon species. Extensive cyclization in the presence of acid, which was attributed to the steric effects among numerous reaction pathways for the first time, prevents MTMS gelation, whereas gels were obtained from the two-step method with nearly random condensations. The experimental degree of condensation (DC) at the gel point using the two-step procedure was determined to be 0.86, which is considerably higher than that predicted by the current accepted theories. Both chemical and physical origins of this high value were suggested. Aerogels dried by supercritical CO2 extraction were characterized by FTIR, 13C and 29Si solid-state NMR and nitrogen sorption. The existence of three residual groups (Si-OH, Si-OCH3, and Si-OC2H5) was confirmed, but their concentrations are very low compared to silica aerogels. The low concentrations of the residual groups, along with the presence of Si-CH3, make MTMS aerogels permanently hydrophobic. To enhance applicability, MTMS aerogels were successfully prepared that demonstrated shrinkage less than 10% after supercritical drying; proving that the rigidity of the gel network is not the sole factor, suggesting in the literature, to cause the huge shrinkage in many hybrid aerogels reported. An important finding of this work is that MTMS aerogels can be prepared without tedious solvent exchange and surface modification if the molar ratio of water/MTMS increases to 8, substantially reducing the cost of aerogel production. This result was attributed to MTMS's fully condensation and low concentrations of ring species.

The fascinating physical properties that arise in materials limited to dimensions of 1-100 nm have gained noteworthy interest from the scientific community. Accordingly, there has been a lot of attention paid to the synthesis of discrete nanoparticles (NPs) and they are being investigated for a range of advanced technologies. Nonetheless, efficient use of nanomaterials in device applications require them to be assembled into solid state macro-structures while retaining their unique, nanoparticulate properties. To date, most commonly investigated assembling techniques include: covalent coupling of NPs surface groups, control evaporation of the solvent to produce ordered supercrystals or non-ordered glassy films, and polymer or bimolecular mediated self-assembly. However, in each of these cases, the interactions among discrete NPs are mediated by intervening ligands, the presence of which are detrimental for efficient electronic transport and interparticle coupling that limit performance in optoelectronic,electro-catalytic, and chemical sensor studies. Thus, novel and efficient strategies that can be predictably manipulated for direct, self-supported assembly of NPs are of critical need. A method that has proved useful to construct direct interfacial linkages of colloidal NPs is the sol-gel technique.Oxidative removal of surfactant ligands has been shown to produce self-supported NP monoliths that in most cases retain the physical properties of primary NPs.The ability to create direct interfacial bonds contributes to enhanced electrical and thermal transport as well as tunable interparticle interactions, expanding the potential range of NP technologies. During oxidation, low coordinated active sites are produced on the NP surface that interacts with a nearby NP to reduce the surface energy. The formed active sites are highly reactive allowing the NPs to establish direct interfacial linkages, polymerize into low dimensional clusters, and consequently highly porous superstructures that augment the unique, nanoparticulate properties. An added advantage of this chemistry is the ability to couple chemically similar or dissimilar systems with the potential to achieve novel/tunable physical properties. In this dissertation, application of sol-gel chemistry in efficient integration of similar and dissimilar nanoscale materials will be discussed with an aim of achieving improved optoelectronic and electro-catalytic properties. Hybrid nanomaterials composed of metal-semiconductor components exhibit unique properties in comparison to their individual counterparts, making them of great interest for optoelectronic technologies. The direct cross-linking of NPs via sol-gel chemistry provides a versatile route to tune interfacial interactions in a manner that has not been thoroughly investigated. Thus, the first part of the dissertation will illustrate the synthesis of CdSe/Ag hetero-nanostructures (aerogels) via oxidation induced self-assembly of thiol-coated NPs and investigate the evolution of optical properties as a function of Ag composition. Two hybrid systems were investigated, where the first and second excitonic energies of CdSe were matched with plasmonic energy of Au and Ag NPs. The optical properties of the CdSe/Ag hybrids were systematically examined through UV-visible, photoluminescence, and time resolved photoluminescence spectroscopy. A new emission (640 nm) from CdSe/Ag aerogels was emerged at Ag loading as low as 0.27 % whereas absorption band tailing and PL quenching effects were observed at higher Ag and Au loading, respectively. The TRPL decay time of the new emission (~600 ns) is markedly different from those of the band-edge (1.83 ± 0.03 ns) and trap state (1190 ± 120 ns) emission maxima of phase pure CdSe, supporting the existence of alternate radiative relaxation pathways in sol-gel derived CdSe/Ag hybrids. An added benefit of newly developed sol-gel chemistry is the potential to produce porous, conducting nanoarchitectures that provide a facile pathway for efficient transfer of charge carriers and small molecules. Thus, aerogels composed entirely of noble metal NPs are expected to exhibit high electrical conductivity making them promising for electrocatalysis. Thus, the second part of the dissertation will describe the extension of NP condensation strategy for the fabrication of ternary noble metal (Au/Ag/Pd, Au/Ag/Pt) aerogels for electro-oxidation of alcohols. The precursor alloy NPs were produced via stepwise galvanic replacement of thiol-coated Ag NPs. The resultant alloy NPs were self-assembled into large, free-standing aerogels that exhibit direct interparticle connectivity, high surface area (282 – 98 m2/g) and mesoporosity (2 – 50 nm) via controlled oxidation of the surfactant ligands. The gelation kinetics has been controlled by varying the oxidant/surfactant molar ratio that governs the dealloying of Ag from ternary superstructures with in-situ generated HNO3. The monolithic Au/Ag/Pd alloy aerogels exhibit higher catalytic activity and durability compared to the discrete alloy NPs (~ 20-30 times) and commercial Pd/C catalyst (2-3 times). On the other hand, Au/Ag/Pt alloy aerogels showed excellent stability at higher concentration of methanol (12 M) during electro-oxidation studies, suggesting its superior electro-catalytic activity. The synergistic effect of tri-metallic alloy mitigates the catalyst poisoning and increases the stability and durability whereas the self-supported superstructure with direct interparticle connectivity, high surface area and porosity offers a facile conduit for molecular and electronic transport, enabling the ternary aerogels an efficient electro-catalyst.

This work utilized the sol-gel process in two ways. First, macroporous silica thin films were developed using a combination of casting techniques and templating. Macroporsity was introduced to the silica thin films by either doping the silica sol before casting or by ordering the template on a substrate and then casting a sol over it. These techniques were first used to create silica thin films with long microchannel pores (200 nm x 60 µm) from a doped sol with the bacteria, B. Megaterium, as the template for nanomaterial formation. To enable the formation long microchannels, the flexible bacteria chains were aligned by using light scratches on the substrate surface as anchors for the bacteria’s adhesive cell capsule. Polystyrene (PS) sphere templates were then used in several studies to obtain silica thin films with well-ordered “nanowells,” single-layer hemispherical pores that allowed direct access to the substrate beneath the film. Copper and gold nanoparticles were integrated into moderately packed films by electrodepostion and monolayer self-assembly, respectfully. The size of the nanoparticles was controlled by the time of the electrodeposition or the time of exposure to an electroless growth solution. The final study with polystyrene latex sphere templates produced high quality, well-packed films containing well-defined nanowells over almost the entire conductive substrate. This was accomplished by separating the ordering of the templates on the substrate from film formation. Electroless growth was used to control the size and shape of the gold nanoparticles and the electrochemical properties of the resultant films were studied, showing an enhanced response to negatively charged redox probes. Sol-gel techniques were then used to create high aspect ratio silica nanotubes and pillars. The electroassisted deposition of silica was carried out in the pores of track-etched membranes, allowing supported nanotubes with dimensions of 100 – 400 nm x 10 µm to be obtained. The mechanism of silica formation in the tubular template was studied and it was found that growth occurred first by nanotube formation, followed by further growth through tube from the electrode to the other side of the pore. This allowed for partially filled tubes and solid pillars to be obtained. The method was found to be flexible and characteristics such as tube length, chemical functionality and porosity to be controlled.