<p>Obtaining full-field \emph{dynamic} material state awareness would have profound and wide-ranging implications across many fields and disciplines. For example, achieving dynamic state awareness in soft tissues could lead to the early detection of pathophysiological conditions. Applications in geology and seismology could enhance the accuracy of locating mineral and hydrocarbon resources for extraction or unstable subsurface formations. Ensuring safe interaction at the human-machine interfaces in soft robotic applications is another example. And as a final representative example, knowing real-time material dynamics in safety-critical structures and infrastructure can mitigate catastrophic failures. Because many materials (e.g., carbon fiber-reinforced polymers composites, ceramic matrix composites, biological tissues, cementitious and geological materials, and nanocomposites) exhibit coupling between their mechanical state and electrical transport characteristics, self-sensing via the piezoresistive effect is a potential gateway to these capabilities. While piezoresistivity has been mostly explored in static and quasi-static conditions, using piezoresistivity to achieve dynamic material state awareness is comparatively unstudied. Herein lies the significant gap in the state of the art: the piezoresistive effect has yet to be studied for in-situ dynamic sensing.</p> <p><br></p> <p>In this thesis, the gap in the state of the art is addressed by studying the piezoresistive effect of carbon nanocomposites subject to high-rate and transient elastic loading. Nanocomposites were chosen merely as a representative self-sensing material in this study because of their ease of manufacturability and our good understanding of their electro-mechanical coupling. Slender rods were manufactured using epoxy, modified with a small weight fraction of nanofillers such as carbon black (CB), carbon nanofibers (CNFs), and multi-walled carbon nanotubes (MWCNTs), and subject to loading states such as steady-state vibration at structural frequencies ($10^2-10^4$ Hz), controlled wave packet excitation, and high-strain rate impact loading in a split-Hopkinson pressure bar. This work discovers foundational principles for dynamic material state awareness through piezoresistivity. </p> <p><br></p> <p>Three major scholarly contributions are made in this dissertation. First, an investigation was pursued to establish dynamic, high-strain rate sensing. This investigation clearly demonstrated the ability of piezoresistivity to accurately track rapid and spatially-varying deformation for strain rates up to $10^2$ s$^{-1}$. Second, piezoresistivity was used to detect steady-state vibrations common at structural frequencies. Utilizing simple signal processing techniques, it was possible to extract the excitation frequency embedded into the collected electrical measurements. The third contribution examined the dynamic piezoresistive effect through an array of surface-mounted electrodes on CNF/epoxy rods subject to highly-controlled wave packet excitation. Electrode-spacing adjustments were found to induce artificial signal filtering by containing larger portions of the injected wave packets. The strain state in the rod was found after employing an inverse conductivity-to-mechanics model, thereby demonstrating the possibility of deducing actual in-situ strains via this technique. A digital twin in ABAQUS was constructed, and an elastodynamic simulation was conducted using identical dynamic loading, the results of which showed very good agreement with the piezo-inverted strains. </p> <p><br></p> <p>This work creates the first intellectual pathway to full-field dynamic embedded sensing. This work has far-reaching potential applications in many fields, as numerous materials exhibit self-sensing characteristics through deformation-dependent changes to electrical properties. Therefore, \emph{piezoresistive elastodynamics} has the incredible potential to be applied not just in structural applications but in other potentially innovated applications where measuring dynamic behavior through self-sensing materials is possible.  </p>

Inorganic-organic hybrid materials have been developed using sol-gel reactions of a trialkoxysilylated organic compound and a metal or semi-metal alkoxide and applied as coatings on polymeric or metallic substrates. Many of these coatings have demonstrated good to excellent abrasion resistance. Abrasion resistant coatings were prepared by hydrolysis and condensation of mixtures of a triethoxysilylated diethylenetriamine (f-DETA), tetramethoxysilane (TMOS), water and an alcohol in the presence of an acid catalyst (a one-step hydrolysis approach). The influences of many formulation and processing variables on the gelation time, optical properties, hardness and abrasion resistance were investigated. An aminolysis mechanism was also proposed to explain the adhesion between sol-gel derived coatings and polycarbonate substrates promoted by a 3-aminopropyltriethoxysilane (3-APS) primer. FT-IR, GPC, 1H and 13C NMR, XPS experiments were conducted to support this mechanism. The f-DETA/TMOS system is essentially a binary system of an alkyltriethoxysilane (T) and a tetraalkoxysilane (Q). At pH 0-2 and pH 4-5, the relative condensation reactivities of the T and Q species in this system were compared using 29Si NMR spectroscopy. After thermal curing, 13C or 29Si solid state NMR spectroscopy was used to estimate the extent of hydrolysis of the urea linkages in f-DETA, the concentration of residual alkoxysilane groups, and the extent of condensation for both T and Q species. The dependence of the morphology of f-DETA/TMOS gels on the pH and the water concentration was also investigated using AFM, SEM and SAXS. Many other trialkoxysilylated organic compounds containing urea, urethane, epoxy and siloxane linkages were also synthesized and utilized to prepare abrasion resistant coatings via a one-step hydrolysis approach, a two-step hydrolysis approach or a moisture-curing approach. Coatings derived from many of these systems or approaches demonstrated abrasion resistance comparable to that of the f-DETA/TMOS coating. Thin coatings were also derived from cubic octasilicate monomers via hydrosilylation or sol-gel reactions. These coatings were very transparent but unfortunately lacked abrasion resistance. / Ph. D.

<p dir="ltr">Increasing power density and power consumption in electronic devices require heat dissipating components with high thermal conductivity to prevent overheating and improve performance and reliability. Polymers offer the advantages of low cost and weight over conventional metallic components, but their intrinsic thermal conductivity is low. Previous studies have shown that the thermal conductivity of polymers can be enhanced by aligning the polymer chains or by adding high thermal conductivity fillers to create percolation paths within the polymeric matrix. To further enhance the in-plane thermal conductivity, the conductive fillers can be aligned preferentially, but this leads to a lower increase in performance in the cross-plane direction. Yet, the cross-plane thermal conductivity plays a vital role in dissipating heat from active devices and transmitting it to the surrounding environment. Alternatively, when the fillers are aligned to enhance cross-plane thermal transport, the enhancement in the in-plane direction is limited. There is a need to develop polymer composites with an approximately isotropic increase in thermal performance compared to their neat counterparts.</p><p dir="ltr">To achieve this goal, in this study, I combine conductive fibers and fillers to enhance thermal conductivity of polymers without significantly inducing thermal anisotropy while preserving the mechanical performance of the matrix. I employ three approaches to enhance the thermal conductivity () of thermoset polymeric matrices. In the first approach, I fabricate thermally conductive polymer composites by creating an emulsion consisting of eutectic gallium indium alloy (EGaIn) liquid metal in the uncured polydimethylsiloxane (PDMS) matrix. In the second approach, I infiltrate mats formed from chopped fibers of Ultra High Molecular Weight Polyethylene (UHMWPE) with an uncured epoxy resin. Finally, the third approach combines the two previous methods by infiltrating the UHMWPE fiber mat with an emulsion of the liquid metal and uncured epoxy matrix.</p><p dir="ltr">To evaluate the thermal performance of the composites, I use infrared thermal microscopy with two different experimental setups, enabling independent measurement of in-plane and cross-plane thermal conductivity. The results demonstrate that incorporating thermally conductive fillers enhances the overall conductivity of the polymer composite. Moreover, I demonstrate that the network structure achieved by the fiber mat, in combination with the presence of liquid metal, promotes a more uniform increase in the thermal conductivity of the composite in all directions. Additionally, I assess the impact of filler incorporation and filler concentration on matrix performance through tension, indentation, and bending tests for mechanical characterization of my materials.</p><p dir="ltr">This work demonstrates the potential of strategic composite design to achieve polymeric materials with isotropically high thermal conductivity. These new materials offer a solution to the challenges posed by higher power density and consumption in electronics and providing improved heat dissipation capabilities for more reliable devices.</p>

This study addresses the critical environmental issue of elevated nitrate levels in water bodies, primarily due to excessive use of nitrogenous fertilizers and improper waste disposal. It focuses on reducing nitrate concentrations in polluted water to permissible levels through the effectiveness of hybrid materials in nitrate adsorption. We synthesized nine amino-functionalized adsorbents using grafting and sol-gel techniques. Batch adsorption tests confirmed the high nitrate adsorption capacities of these adsorbents, with sol-gel materials showing the highest efficiency due to their abundant amino group contents. Among these, the surfactant-free, sol-gel adsorbent was the most effective, combining ease of synthesis with cost-efficiency. Our study of temperature dependence revealed optimal nitrate removal at ambient conditions and decreased capacity at higher temperatures. These adsorbents remained highly efficient over five adsorption/regeneration cycles. This research significantly advances efficient nitrate removal methods, presenting a promising approach for environmental remediation.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Hybrid graft copolymers of polystyrene (PSty) and polydimethylsiloxane macromonomers (PDMS) were synthesised. PSty-g-PDMS was synthesised employing the grafting through technique via a conventionally free radical polymerization (FRP) using a polydimethylsiloxane macromonomer. In this series the amount of PDMS incorporated into the copolymer was varied by varying the macromonomer to styrene ratios as well as the length of the PDMS side chain. This allows for the study of the effect that the macromonomer content and the branching length has on the efficiency of the grafting process. A second series of PDMS-g-PSty was also synthesized where the PDMS forms the backbone and the PSty the grafts. Two synthetic techniques were employed for the formation of these polymers. Firstly, the grafting onto approach was used where functional polystyrene prepolymers with either an allyl or vinyl end-groups were synthesised anionically (living anionic polymerization) prior to the coupling of a functional prepolymer using a hydrosilylation reaction with a Karstedt platinum catalyst. This technique was successful and gave insight to the effect of the polystyrene prepolymer graft length has on the grafting efficiency as well as the functional groups needed on the PDMS backbone. Furthermore, the effect of the viscosity (of the PDMS macromonomer) plays on the grafting efficiency was also elucidated. Lastly, the grafting from approach was employed for the formation of PDMS-g-PSty. ATRP, atom transfer radical polymerization, of styrene using a bromoisobutyrate functional PDMS macroinitiator was used for the synthesis of these copolymers. This was accomplished by reacting commercial silane functional PDMS molecules via a hydrosilylation reaction (using a Karstedt catalyst) with allyl-2- bromo-2-methyl-propionate to give a PDMS macroinitiator with bromoisobutyrate functional groups. This will allow for the initiation and growth of polystyrene branches from the PDMS backbone (employing ATRP with a suitable catalyst and ligand). The formation of the endproduct, PDMS-g-PSty, via this route proved to be extremely difficult and largely unsuccessful. Liquid chromatography (LC) at the critical point (LCCC) of polystyrene was used to separate the graft material from homo-polymers which might have formed as well as from the PDMS macromonomer. This technique allows for a very fast chromatographic analysis of the grafting reaction. Under the critical conditions of PSty it was found that the graft copolymer eluted at a lower retention time than the unreacted macromonomer and PSty homopolymer. Two-dimensional chromatography, where LCCC (1st dimension) was coupled to size exclusion chromatography (2nd dimension), was used for the evaluation of the CCD and MMD (molecular mass distribution) of the graft material. LC was furthermore coupled off-line to FTIR and TEM using an LC interface. LCFTIR gave insight to the microstructure of the material, whilst LC-TEM gave insight to the morphological nanostructure of the material. / AFRIKAANSE OPSOMMING: Hibried ent-kopolimere is gesintetiseer uit polistireen (PSty) en polidimetielsiloksaan (PDMS). PSty-g-PDMS is gesintetiseer deur gebruik te maak van die ent-deur tegniek via ‘n konvensionele vrye radikaal polimerisasie proses (VRP). In die reeks is die hoeveelheid PDMS wat geïnkorporeer is, gevarieer deur die hoeveelheid PDMS tot PSty verhouding te verander asook die lengte van die PDMS sytak. Gevolglik het dit toegelaat vir die studie van die effek wat die makromonomeer inhoud, sowel as die taklengte het op die effektiwiteit van die ent-proses. ‘n Tweede reeks is ook gesintetiseer, waar die PDMS die ruggraat vorm van die ko-polimeer, en die stireen die takke vorm van die ko-polimeer. Dus is PDMS-g-PSty gesintetiseer. Twee sintetiese tegnieke is benut vir die vorming van die kopolimere. In die eerste geval is daar van die ent-op tegniek gebruik gemaak waar funksionele polistireen prepolimere met ‘n alliel of ‘n silaan end-groep gesintetiseer is deur gebruik te maak van ‘n anioniese lewendige polimerisasie voor die koppeling van die PDMS makromonomere deur ‘n hidrosililasie proses met ‘n Karstedt platinum katalisator. Die tegniek was suksesvol en het in diepte insig gegee van die effek wat die molekulêre lengte van die polistireen prepolimeer het op die effektiwiteit van die ent-proses, sowel as die minimum hoeveelheid funksionele groepe wat teenwoordig moet wees op die PDMS ruggraat. Verder is die effek wat die viskositeit (van die PDMS makromonomeer) op die ent-proses het, bekend gemaak. Laastens is daar ook van die ent-vanaf tegniek gebruik gemaak vir die vorming van PDMS-g-PSty. AORP, atoom oordrag radikale polimerisasie, van stireen, deur gebruik te maak van ‘n bromoisobutiraat funksionele PDMS makro-inisieerder, is gebruik vir die sintese van die kopolimere. Die makro-inisieerders is bekom deur gebruik te maak van kommersiële silaan funksionele PDMS, en dit is gereageer deur middel van ‘n hidrosililasie proses met alliel-2-bromo- 2-metiel-propionaat. Dit het PDMS makroinisieerders tot gevolg gehad met bromoisobutiraat funksionele groepe. Gevolglik kon stireen takke vanaf die PDMS ruggraat gegroei word deur gebruik te maak van AORP met ‘n geskikte katalisator en ligand. Die vorming van die end-produk, PDMS-g-PSty, deur middel van hierdie roete was onsuksesvol. Vloeistof chromatografie by die kritiese punt van polistireen was gebruik om die ent-produk te skei van die homo-polimere en PDMS makromonomeer. Gevolglik kon die chemiese samestelling van die ent-produk geëvalueer word. Twee-dimensionele chromatografie, waar vloeistof chromatografie by die kritiese punt van polistireen in die eerste vlak gekoppel was aan grootte uitsluitings chromatografie in die tweede vlak, was benut om die chemiese komposisie sowel as die molekul re massa verdeling van die entproduk te verkry. Verder was vloeistof chromatografie indirek aan Fourier-oordrag infrarooi en transmissie elektron mikroskopie (TEM) gekoppel. Eergenoemde het insig gegee tot die mikrostruktuur van die materiaal, terwyl laasgenoemde insig gegee het tot die morfologiese nanostruktuur van die materiaal.

La cellulose, composé organique le plus courant et polysaccharide le plus abondant sur Terre, est une ressource naturelle très importante. Les initiatives pour remplacer totalement ou partiellement les polymères pétrochimiques conventionnels avec des bio-polymères à base de cellulose ont donc attiré l'intérêt des chercheurs ces dernières décennies, non seulement parce que la cellulose est renouvelable et biodégradable, mais aussi en raison de ses propriétés intéressantes telles que la biocompatibilité et la stabilité chimique. De plus, les propriétés de cellulose peuvent être encore améliorées par des procédés chimiques, des modifications physiques ou en préparant des composites avec des charges fonctionnelles.Les études concernant d'étudier plusieurs aspects fondamentaux comme la dissolution de la cellulose afin de produire des matériaux et le test de nouveaux concepts autour de la modification de surface ou des revêtements, à l'échelle du laboratoire. Nous présentons dans ce manuscrit nos travaux concernant la caractérisation de solutions de cellulose dans deux solvants différents (hydroxyde de sodium aqueux et un liquide ionique) et la préparation de deux nouveaux types de matériaux à base de cellulose (un matériau hybride cellulose-amidon et un composite cellulose-noir de carbone), qui sont tous les deux préparés à partir de ces solutions de cellulose. / Cellulose, as the most common organic compounds on Earth, and also the most abundant polysaccharide, is definitely an important natural resource. With the initiatives of replacing (partially) the conventional petrochemical polymers by bio-based polymers, cellulose has regained the researchers' interests in the last few decades, not only because it is renewable and biodegradable, but also due to interesting properties such as biocompatibility and chemical stability. Additionaly, cellulose properties can be further enhanced by chemical/physical modification or making composites with functional fillers.This study was to investigate several fundamental scientific aspects as cellulose dissolution, making cellulose-based materials from solutions, and test of new concepts as surface modification or coating at laboratory scale. We studied and will present in this manuscript the characterization and properties of both cellulose solutions in different solvents (aqueous sodium hydroxide and ionic liquid) and two types of cellulose-based hybrid materials (one with starch and the other with carbon black), which were all prepared from dissolved cellulose.

Ce manuscrit de thèse décrit la conception, l’élaboration et l’étude de complexes organofers électro-actifs dans lesquels deux unités terminales Cp*(dppe)FeII/III sont reliés par un pont fonctionnel. Dans le premier chapitre, nous avons présenté une réaction à la fois originale et efficace catalysée par le Pd(0) qui permet d’accèder à la [5,5’-{(Cp*(dppe)Fe–C≡C}2-(μ-2,2’-bipy)]. Le deuxième chapitre porte sur la présentation d’une voie de synthèse rapide et efficace du métallo-ligand [6,6’-{Cp*(dppe)Fe–C≡C}2-(μ-2,2’-bipy)]. Le troisième chapitre de ce mémoire est consacré à l’utilisation du ligand 1’,1’’’-bis(éthynyle)biferrocényle comme pont entre deux terminaisons électroactives Cp*(dppe)FeII/III. L’espaceur électro-actif joue le rôle de relais moléculaire favorisant le transfert électronique d’une terminaison à l’autre par sauts successifs. Afin d’ajuster les potentiels redox des terminaisons par rapport à ceux du biferrocényle, les terminaisons Cp(PPh3)2M (M = Ru, Os) ont également été utilisées pour substituer un ou deux sites organofers. Le chapitre quatre est dédié aux travaux réalisés sur le système hybride Cp*(dppe)Fe-C≡C-TTMe3. Dans cette molécule, le site Cp*(dppe)FeII/III interagit à travers le pont acétylure avec le fragment tétrathiafulvalényle. La nouvelle molécule est stable sous trois degrés d’oxydation. L’espèce monocationique se comporte comme un composé à valence mixte de classe II et le couplage électronique entre les deux électrophores a été déterminé (Hab = 320 cm-1). Dans le cinquième et dernier chapitre nous mettrons à profit la découverte d’une réaction d’activation de la liaison C-H du groupement méthyle situé sur le même cycle du TTF et de l’acétylure de fer dans le composé [Cp*(dppe)Fe-C≡C-TTMe3](PF6)3. Cette réaction permet la synthèse du complexe moléculaire multifonctionnel [Cp*(dppe)Fe=C=C=TTFMe2=CH-CH=TTFMe2=C=C=Fe(dppe)Cp*][PF6]2 avec de très bon rendement. Les propriétés physicochimiques de ce nouveau complexe analysées avec le support de la chimie quantique permettent de révéler les caractéristiques originales de ce composé inédit. / This thesis highlights the conception, synthesis and studies of redox-active organoiron complexes in which the two termini Cp*(dppe)FeII/III are linked by a functional bridge. In chapter I, an original and efficient synthetic Pd(0) catalysed homocoupling procedure is reported involving mononuclear organoiron(II) intermediates allowing us to isolate [5,5’-{Cp*(dppe)Fe–C≡C}2-(μ-2,2’-bipy)]. In chapter II, a rapid and efficient synthetic access to the redox-active metallo-ligand [6,6’-{cp*(dppe)Fe–C≡C}2-(μ-2,2’-bipy)] is described. In chapter III, the synthesis and properties of a series of complexes containing bis(ethynyl)biferrocene as a bridge between different redoxactive groups is pointed out. The redox bridge acts as a molecular relay for the electronic exchange between the termini via an electron hopping pathway. In order to tune the redox potential compared with those of biferrocene, one or two organoiron groups have been substituted by the Cp(PPh3)2M (M = Ru, Os) groups. In chapter IV, works are dedicated to the hybrid system Cp*(dppe)Fe-C≡C-TTMe3. In this molecule, electronic interactions take place between the Cp*(dppe)FeII/III center and the tetrathiafulvalene core through the ethynyl bridge. The new molecule is stable under three redox states. The mono-oxidized species behaves as a mixed valence species with an electronic coupling Hab = 320 cm-1 between the two electrophores. In the fifth and final chapter, the discovery of a CH bond activation of a methyl group located on the same cycle of the TTF core and the iron acetylide for the compound [Cp*(dppe)Fe-C≡C-TTMe3](PF6)3 is reported. This new reaction allows the synthesis of the multicomponent molecule [Cp*(dppe)Fe=C=C=TTFMe2=CH-CH=TTFMe2=C=C=Fe(dppe)Cp*][PF6]2 in good yield. The resulting device displays specific properties analysed with the support of the quantum chemistry.

Ø / The dissertation is presented on 252 content pages which has been framed in five chapters and two annexures while the title page opens into a list of abbreviations followed by a foreword on the work. The core theme of the research work is to validate the extended photocatalytic properties of porphyrin-POM materials in evolving from UV to visible light range of solar spectrum. Which describing additional modes for synthesis of hybrid materials (i) electrostatic multilayer’s comprising of Dawson , sandwich Dawson type and preyssler,s POM in combination with free base tetracationic porphyrin [H₂TPhN(Me)₃P⁴⁺] (ii) an easy method of synthesis of two dimers with a pyridinium spacer (abbreviated 4-H₂–Zn and 3-H₂–Zn) (iii) Langmuir Schafer approach for hybrid monolayer. The prepared photoactive thin layers have been characterized by UV-visible spectroscopy and fluorescence spectroscopy for optical properties. Cyclic voltammetry for electrochemistry and ionic permeability studies. Atomic force microscopy (AFM) for surface morphology and its role in physical mechanism of reduction process and shape of nanostructures obtained. Transmission electron microscopy (TEM) has been used to interpret size and shape of dendritic silver nanoparticles obtained as photoreduction product. Although ,the ultimate goal is the photoreduction of heavy metals (Cr(VI), Hg(II), Cd(II), Pb(II) ), reduction of a simpler system like Ag⁺ ion has been chosen as a model system due to single electron simpler oxidation reduction process. A novel application of photocurrent generation from these hybrid films has been demonstrated in the fifth chapter of the manuscript as an initial studies which has enhanced the significance of all previously fabricated systems upto by many folds .The foresaid development of photovoltaic application has paved the way for future studies to enhance the photocurrent yield further by tuning the electron donor-acceptor system. Both components porphyrin and POM can be tuned with different axial substituent’s and stereo chemical properties to achieve maximum yield of solar energy as well as diversified metal nanostructure for nanoelectronics, e.g. silver dendrites for sensor applications. At the end of the manuscript, three appendices describe successively the experimental techniques used to carry out this work, the Job method used to determine the stoichiometry and formation constants of complex electrostatic and coordination, and then finally the origin or Protocols for the synthesis of various compounds used.

Nesse trabalho são discutidos os resultados a respeito de materiais híbridos baseados na poliimida, PI, obtida por reações de policondensação entre a diamina 4,4\'-Oxidianilina (ODA) e o dianidrido 4,4\'-Oxidiftálico (ODPA), seguida de imidização térmica. O estudo foca na influência do tempo de tratamento (1, 15 e 60 min) e na temperatura de decomposição térmica (500°C) sobre as propriedades da PI. Os experimentos foram realizados sob fluxo de Argônio e os materiais obtidos apresentam características intermediárias entre PI e materiais carbonáceos. Dados de Nanoindentação (NI) revelaram aumento de até 50% de dureza para os filmes tratados por 60 min. ODPA e ODA serviu ainda de base para a preparação do revestimento híbrido contendo ORMOSIL gerado in situ por catálise ácida via processo sol-gel a partir do (3-aminopropil)trietóxissilano (APTES) e Tetraetil Ortossilicato (TEOS). O revestimento obtido é homogêneo e tem boa interação com o substrato (aço inoxidável 316L). A polarização potenciodinâmica revelou uma proteção elevada tanto em solução de NaCl 3,5% em massa quanto em H2SO4 0,5 mol L-1, em relação ao aço sem revestimento, com densidade de corrente da ordem de 10-9 A cm-2, na faixa de -700 a 500 mV vs Ag/AgCl. Por fim, filmes híbridos baseados em ODPA, ODA, APTES e TEOS, adicionados de Ácido Fosfotungstico (HPW) foram preparados e avaliados por Espectroscopia na região do Infravermelho com Transformada de Fourier e Ressonância Magnética Nuclear de Silício e Fósforo (29Si e 31P MAS NMR) que confirmaram a formação da PI e da rede ORMOSIL, bem como revelam que a estrutura do HPW permaneceu intacta após o processo de síntese. Mapeamentos realizados por Micro-fluorescência de Raios X assistida por Luz Síncrotron (&#956;-XRF) mostram uma boa dispersão da fase inorgânica (ORMOSIL e HPW) na orgânica (POO), e todos os materiais são termicamente estáveis até aproximadamente 500°C, de acordo com as curvas obtidas por Termogravimetria (TGA). Outras técnicas de caracterização também foram usadas para uma investigação mais detalhada dos materiais. / In this thesis are presented the results and considerations related to several hybrid materials derived from the polyimide, PI, obtained by polycondensation reactions between 4,4\'-Oxydianiline (ODA) and 4,4\'-Oxydiphthalic (ODA), followed by thermal imidization. The study focuses on the effect of thermal treatment time (1, 15 and 60 min) and the temperature of beginning of thermal decomposition (773 K) on the properties of PI. The experiments were performed under Argon flow, and the materials presented intermingled properties of PI and carbonaceous materials. The hardness, evaluated by Nanoindentation (NI), reached an increase of 50% for POO films treated for 60 min. POO was also used for the preparation of the hybrid coating containing ORMOSIL obtained in situ by acid catalysis via sol-gel process from (3-aminopropyl)triethoxysilane (APTES) and Tetraethyl Orthosilicate (TEOS). The coating is homogeneous and present a good interaction with the substrate (316L stainless steel). Data of potendynamic polarization revealed a high protection both under NaCl 3.5 wt% and H2SO4 0.5 mol L-1 solutions related to the neat substrate, with current density of order 10-9 A cm-2, in range potential of -700 to 500 mV vs Ag/AgCl. Finally, hybrid films were prepared based on ODPA, ODA, APTES and TEOS, in addition to Phosphotungstic Acid (HPW). The characteristics of all materials were evaluated by Fourier Transform Infrared Spectroscopy in Middle and Near Infrared region (FTMIR and FTNIR), and Magic Angle Spinning-Nuclear Magnetic Resonance of Silicon 29 and Phosphorus 31 (29Si and 31P MAS NMR) which confirmed the ORMOSIL network formation, as well as revealed that the HPW structure remained intact after the synthesis process. Mapping performed by Assisted Synchrotron Light X-ray Micro Fluorescence (&#956;-XRF) the good dispersion of the inorganic phase (ORMOSIL and HPW) in the organic phase (POO). All materials are thermally stable up to 773 K, according to Thermogravimetric Analysis (TGA). Other techniques of characterization were also used to further investigation of the materials.

Filmes híbridos fotoativos de Ormosil (silicatos organicamente modificados) contendo o polioxometalato de Keggin ácido fosfotungstico (H3PW12O40) e cátions Ag+ foram preparados por meio da rota sol-gel e deposição de filme por dip-coating. A caracterização por FTIR, Raman, XRF e DRX evidenciou a formação da matriz de organossilicato e o aprisionamento dos poliânions PW12O403- e cátions Ag+. O comportamento fotocrômico dos filmes de Ormosil-fosfotungstato baseiam-se na redução fotoinduzida do fosfotungstato por exposição à radiação UV, o que leva à formação de compostos coloridos de valência mista conhecidos como heteropolyblues. No entanto, a presença de cátions Ag+ altera completamente o comportamento fotocrômico destes filmes híbridos. Os poliânions de fosfotungstato fotorreduzidos são agentes redutores eficientes na redução dos cátions Ag+, resultando na formação in situ de nanopartículas de prata metálica na matriz híbrida como evidenciado pela intensa banda plasmônica centrada em 390 nm no espectro eletrônico da amostra. A caracterização por Uv-vis e Espectroscopia de Absorção de Raios X próxima a Borda de Absorção (XANES) mostrou que a foto-redução pode ser revertida por tratamento térmico o que caracteriza um comportamento fotocrômico reversível. O comportamento cinético da amostra foi analisado propondo mecanismos para as reações de redução e oxidação da prata, responsáveis pela alteração de coloração do material. O aprisionamento de compostos fotoativos em matrizes híbridas orgânico-inorgânico via sol-gel é uma estratégia interessante para a preparação de materiais fotocrômicos com potenciais aplicações tecnológicas. A reversibilidade fotocrômica destes materiais os torna bons candidatos para aplicação em sistemas de memória óptica, filtros óticos de passa-banda estreita, dispositivos de ótica não linear, sensores de radiação UV e revestimentos bactericidas. / Sol gel entrapment of photoactive compounds in organic-inorganic hybrid matrices is an interesting strategy for the preparation of photochromic materials with potential technological applications. In this study, we report the preparation of photoactive Ormosil (organically modified silicates) hybrid films containing the Keggin polyoxometalate phosphotungstate (H3PW12O40) and Ag+ cations by sol-gel synthesis and dip coating deposition. The materials have been characterized by infrared absorption spectroscopy (FTIR), Raman spectroscopy and X-ray Fluorescence (XRF), thus evidencing the formation of hybrid organosilicate matrix and the entrapment of the PW12O40-3 polyanions and Ag+ cations. The photochromic behavior of the Ormosil-phosphotungstate films is based on photoinduced reduction of phosphotungstate upon exposure to UV radiation, which leads to the formation of colored mixed valence compounds known as heteropolyblues. However, the presence of Ag+ cations completely changes the photochromic behavior of these hybrid films. The photoreduced phosphotungstate polyanions rapidly promote the reduction of Ag+ cations, resulting in the in situ formation of silver metal nanoparticles (Ag0) inside the hybrid matrix as evidenced by the intense plasmonic band centered at 390nm as shown by electronic, UV-vis, spectroscopy and its yellowish color. The Uv-vis and X-ray Near Edge Absorption Spectroscopy (XANES) characterization shown that this process is reversible and the yellowish color characteristic of the metallic silver nanoparticles disappears once the hybrid films are heated at 353 K. Thus, the coloration is achieved upon UV exposure and discoloration occurs upon simple heating. Therefore, the described photoactive properties, the prepared hybrid films have potential application in optical memory systems, single bandpass optical filters, non-linear optical devices, UV radiation sensors and bactericidal coatings.