É grande o uso do alumínio em virtude de sua viabilidade técnica e econômica além da alta proteção frente à corrosão conferida pelo filme de óxido de alumínio formado em sua superfície. Neste trabalho foram realizadas deposições de filme de polianilina (PAni) sobre ligas de alumínio AA-2014, AA-2024 e 7075 O. Os experimentos de eletropolimerização foram realizados por voltametria cíclica e cronoamperometria a partir de soluções aquosas contendo ácido fosfórico, ácido sulfâmico e anilina. Para a caracterização dos filmes obtidos sobre as superfícies das ligas foram utilizadas as técnicas de espectroscopia de infravermelho, microscopia eletrônica de varredura e espectroscopia de impedância eletroquímica. Os ensaios de corrosão foram realizados em meio agressivo ao alumínio, solução aquosa de NaCl 0,6 mol L-1 por medidas de polarização potenciodinâmica. Também foi estudada a nucleação dos filmes de PAni por cronoamperometria sobre as mesmas ligas. A partir da caracterização dos polímeros, os resultados demonstram diferenças estruturais entre os filmes de PAni decorrentes do meio ácido utilizado na eletropolimerização, que influencia na proteção contra corrosão. Estruturalmente os filmes eletropolimerizados em meio de ácido fosfórico são mais porosos em relação ao filme de PAni obtido em meio de ácido sulfâmico. Tanto para os filmes obtidos a partir de soluções aquosas de ácido fosfórico como de ácido sulfâmico ocorreram variações estruturais dos filmes após os ensaios de corrosão. Os parâmetros eletroquímicos extraídos das curvas potenciodinâmicas e das análises de impedância demonstram que os filmes obtidos protegem as ligas estudadas contra corrosão. Considerando-se o filme no estado desdopado, para a liga AA-2014, houve um deslocamento no potencial de corrosão de 61,2 mV para valores mais positivos em relação a liga sem recobrimento. Para as outras ligas esse deslocamento foi de 176,1 mV para a liga AA-2024 e 134,3 mV para a liga 7075, evidenciando assim uma maior proteção contra corrosão. Os estudos de corrosão evidenciam que os filmes de PAni podem ser alternativas viáveis aos outros meios protetores utilizados contra corrosão. / Aluminum is widely used due to its technical and economic advantages, as well as due to its high level of corrosion protection provided by the oxide film formed on the surface of the metal. In the current study deposition of polyaniline (PAni) on three different Al alloys (AA-2014 F, AA-2024 T3 and 7075 O) was studied. The electrodepositions were realized from aqueous solutions of either phosphoric acid or sulphamic acid that contained the aniline monomer, using the techniques of cyclic voltammetry and chronoamperometry. The films were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). To evaluate the resistance of the films under conditions aggressive to Al, potentiodynamic polarization curves were performed in 0,6 mol L-1 NaCl. The nucleation of the films on the aluminum alloys was also investigated using chronoamperometry. Characterization of the PAni films obtained demonstrates that the use of different acids results in distinct structural characteristics, which influence their corrosion protection properties. Structurally the electro-deposited PAni films are more porous when phosphoric acid is used compared to sulphamic acid. After the corrosion assays structural differences are observed, independent of the acid used in the electrosynthesis. Data obtained from the potentioidynamic polarization curves and the impedance measurements indicate that the films obtained protect the alloys studied against corrosion. Considering the film in the undoped form for the alloy AA-2014 F, there was a positive shift in the corrosion potential of 61.2 mV. For the AA-2024 T3 and 7075 O alloys the shifts were 176.1 and 134.4 mV, respectively, indicating a greater degree of corrosion protection. The present study demonstrates that PAni films are viable alternatives to other protection methods.

O estudo dos polímeros condutores tem sido bastante intensificado nos últimos anos devido a grande aplicabilidade tecnológica que oferecem. O presente trabalho tem como objetivo contribuir com esses estudos desenvolvendo sensores de polímeros condutores (PAni e POMA e copolímeros de PAni/POMA), para a determinação de compostos orgânicos (Hidroquinona). Os filmes poliméricos foram obtidos por eletropolimerização pela técnica de voltametria cíclica, técnica esta que foi utilizada para as respostas eletroquímicas da hidroquinona em contato com os filmes. A caracterização estrutural dos filmes foi realizada por espectroscopia no ultravioleta e visível e no infravermelho e a caracterização morfológica por microscopia eletrônica de varredura. Os filmes de PAni, POMA e PAOMA em meio de HCl com espessuras de 2,82, 1,1 e 0,039 nm respectivamente apresentaram melhor índice de detecção, já os filmes de PAni, POMA e PAOMA eletrossintetizados em meio de H2SO4, apresentaram melhor índice de detecção com espessuras de 1,34, 1,4 e 0,032 nm, respectivamente. / The study of conducting polymers has intensified in recent years due to their wide range of possible technological applications. The present work the objective of contributing to this area by developing sensors that use conducting polymers (PAni and POMA and copolymers of PAni/POMA) for the determination of organic compounds (Hydroquinone). Polymeric films were obtained by cyclic voltammetry (electropolymerization) in different solutions. The films obtained were subsequently characterized electrochemically ? also using cyclic voltammetry. Structural characterization of the films was performed using ultraviolet spectroscopy (UV-vis) and infrared spectroscopy (IR) with the morphology studied by scanning electron microscopy (SEM). The PAni, POMA and PAOMA films synthesized in HCl presented the best detection indexes at thicknesses of 2.82, 1.10 and 0.039 nm, respectively. The films synthesized in H2SO4 had the best detection indexes at thicknesses of 1.34, 1.40 e 0.032 nm, respectively.

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L'électrorhéologie est un domaine où les possibilités d'accroître les performances en utilisant des composés hybrides organiques-inorganiques ont été explorées. Les fluides électrorhéologiques sont des dispersions de particules colloïdales facilement polarisables par un champ électrique dans un liquide non conducteur. Lorsqu'un champ électrique est appliqué les propriétés rhéologiques changent et la viscosité apparente peut augmenter ou diminuer en fonction du type de particules présentes dans le fluide. Ces fluides appartiennent à la classe des matériaux intelligents qui ont un grand potentiel technologique avec des applications dans de nombreux domaines comme l'automobile, l'hydraulique, les joints d'étanchéité, la robotique, le spatial et même en médecine. Dans ce travail on s'intéresse à trois différentes sortes d'hybride: des silicates avec des molécules organiques (ORMOSIL) modifiés par des groupements mercaptan, des liquides ioniques encapsulés dans la silice, et des fibres de sépiolite recouvertes de polyaniline. Pour la synthèse des particules à base de silice (ORMOSIL) et les liquides ioniques encapsulés dans la silice, on a utilisé le procédé sol-gel. Dans le cas de la polyaniline sur la sépiolite, deux méthodes de polymérisation ont été utilisées: en phase solide et en suspension. Tous les systèmes étudiés ont présenté une réponse électrorhéologique. Parmi eux l'hybride polyaniline/sépiolite a fourni la meilleure réponse électrorhéologique, sans doute à cause de la forme allongée des particules, qui donne une contrainte seuil plus grande que les formes sphériques obtenues pour les hybrides à base de silice. / Electrorheology is an area has been exploring the application of these organic-inorganic hybrid compounds, to obtain better performance in electrorheological properties. Electro-rheological fluids consist of a colloidal dispersion, where the liquid is non-conductive and the particles dispersed in the fluid are able of polarized at presence of electric field. When the fluids ER are subjected to an external electric field the rheological properties change, and may increase or decrease the apparent viscosity, it depending on the type of particle present in the fluid. These fluids fall into the class of smart materials witch were of great technological interest, since they are finding applications in: automotive industrial, hydraulics industrial, fluid sealing, robots, aerospace and medicine, among others. In this work were discussed three different kinds of hybrids: organically modified silanes (ORMOSIL) modified with mercaptans groups, ionic liquid encapsulated by silica and sepiolite fibers coated by polyaniline. For the synthesis of particles concerned silica (ORMOSIL and ionic liquid encapsulated by silica) the sol-gel process was used. In the case of polyaniline and sepiolite two synthetic methods of polymerization were applied: bulk and slurry. All systems studied presented electrorheological response. Among them, the polyaniline/sepiolite hybrid materials was provided the best electrorheological response, probably due to its elongated morphology supplied the yield stress greater than spherical morphologies, which were obtained for silica hybrids.

Ces travaux de thèse consistent à formuler des nanocomposites électriquement conducteurs pour des applications micro-ondes. L’objectif principal est la mise en œuvre de matériaux absorbant les ondes radar, plus particulièrement sur la bande X (8-12 GHz). La polyaniline et les nanotubes de carbone, dispersés dans une matrice époxyde, ont été sélectionnés pour apporter les propriétés d’absorption aux fréquences visées. Différentes morphologies de polyaniline ont été synthétisées afin d’étudier leur influence sur les propriétés d’absorption des composites. L’utilisation d’une polyaniline à morphologie feuillet, présentant une forte anisotropie et un facteur de forme élevé, permet d’augmenter la conductivité et les pertes diélectriques des composites. De plus, leur association avec des nanotubes de carbone améliore significativement les propriétés d’absorption aux fréquences micro-ondes. Des écrans absorbants radar performants qui présentent des coefficients de réflexion inférieurs à -20 dB ont pu être modélisés et mis en œuvre, confirmant le potentiel de ces matériaux pour des applications de furtivité radar. / This thesis deals with the formulation of electrically conductive nanocomposites for microwave applications. The main purpose is to process radar-absorbent materials, more particularly at the X band. (8-12 GHz). Polyaniline and carbon nanotubes, dispersed in an epoxyde matrix, have been selected. Different morphologies of polyaniline have been synthesized to study its impact on the absorption properties of composites. Using flake-like polyaniline showing high anisotropy and aspect ratio increases conductivity and dielectric losses of composites. Moreover, its association with carbon nanotubes significantly improves the absorption properties at microwaves frequencies. Efficient radar absorbing screens, showing reflection losses lower than -20 dB, have been calculated and processed confirming the potential of these materials for stealth applications.