Les élastomères diélectriques sont de plus en plus utilisés pour la réalisation des transducteurs dans de nombreux domaines industriels : interface haptique, robotique, biomimétisme, conversion d’énergie. Pour le fonctionnement de toutes ces applications, le polymère électroactif est soumis à une haute tension (de 1 à 10kV). Toutefois, le courant de fuite diminue l’efficacité et la durée de vie des dispositifs utilisant ces matériaux.Par ailleurs, une précontrainte mécanique (étirement) est généralement appliquée au polymère pour accroître l’efficacité énergétique dans la conversion mécanique-électrique. Les courants de fuite (et donc le champ de claquage du polymère) seront ainsi conditionnés par cette précontrainte et ce point doit faire l’objet d’une étude détaillée.L’objet de ce travail de thèse est de mener des analyses de courant de fuite sur des polymères électroactifs (élastomères polyacrylates du commerce VHB4910 et silicones Sylgard 186) non contraints et contraints mécaniquement pour évaluer l’amélioration ou la dégradation des performances électriques lorsqu’ils seront plus tard intégrés en géométrie électrode-polymère-électrode dans des transducteurs.Tout d’abord, nous avons mené une étude exhaustive sur l’influence des facteurs externes (étirement, température, champ électrique, nature de l’électrode) sur les propriétés électriques du polyacrylate VHB4910. Les études ont été réalisés sur des durées de polarisation courtes (quelques minutes) et longues (jusqu’à 15 heures). Au cours de ce travail, nous sommes également intéressés à l’étude du phénomène d’autocicatrisation sur le sylgard 186. Les tests ont été conduits pour différents types d’électrodes (or, aluminium, graphène, nanoplaquettes de graphène : GnP) déposées sur la surface de silicone. Une analyse par microscopie optique de la zone évaporée a été menée.La finalité de ces travaux aura permis d’optimiser des structures de récupération d’énergie électrostatique à base de polymères électroactifs. / Electroactive polymers known as dielectric elastomers have shown considerable promise for transducers. They are attractive for a wide range of innovative applications including softs robots, adaptive optics, haptic interface or biomedical actuation thanks to their high energy density and good efficiency. For the functioning of all these application, the electroactive polymer is subjected to high electrical field. Nevertheless, the performances of these transducers are affected by the losses and especially the ones induced by the leakage current.Mechanical pre-stretch is an effective method to improve actuation when a voltage is applied to the device made up of a dielectric elastomer sandwiched between two compliant electrodes. The overall performances of the structure (electromechanical conversion, efficiency, strain induced…) depend strongly on the electric and mechanical properties of the elastomer. Regarding electric characteristics, dielectric permittivity, dissipation factor and electric breakdown field have been deeply investigated according to various parameters such as frequency, temperature, pre-stretch, or nature of the electrodes but complete analysis of the leakage current is missing in the scientific literature.Thus, this work reports an extensive investigation on the stability of the current-time characteristics in dielectric elastomer. Particularly, we focus on the influence of the nature of the electrodes and pre-stress applied to the transducer. In order to evaluate the influence of the time duration on the behavior of the leakage current, short and long-term electrical stress times was applied during short times and up to 15 hours.Leakage current in electroactive polymers were discussed for a commercial polyacrylate (VHB4910 from 3M) currently used for soft transducers applications. This current is investigated as a function of external factors (stretching, temperature, type of material for electrodes)In order to evaluate the limitations in term of voltage and in the goal to increase the lifetime of these transducers, the second part of our study is focused on the dielectric strength of silicone rubbers for various types of electrodes (gold, Aluminum, graphene nanoplatelets, graphene : GnP). The effect of self-healing is particularly studied and a selection of electrodes for soft transducers based on dielectric elastomers is proposed.

L'utilisation extensive des combustibles fossiles, l'émission de gaz à effet de serre dans l'atmosphère et les difficultés de recyclage des résidus de consommation incitent au recours accru aux polymères biodégradables. Dans le domaine du génie électrique, de nombreux polymères trouvent des applications dans les systèmes d'isolation des matériels électriques. Ces polymères sont issus du pétrole, peu respectueux de l'environnement et la plupart d'entre eux ne sont pas biodégradables. Dans le but de les remplacer, des polymères biodégradables ont été explorés.Une revue des travaux de recherche sur les polymères biodégradables dans le domaine du génie électrique a été réalisée. Les propriétés thermiques et électriques de polymères biodégradables et conventionnels sont rapportées et comparées.Les polymères biodégradables et / ou biosourcés sélectionnés et mis en œuvre sont le Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), le polycaprolactone (PCL) et l’acide polylactique PLA. Un matériau nanocomposite basé sur PLA a également été préparé. Les propriétés diélectriques pour une large gamme de température et de fréquence ont été mesurées par spectroscopie diélectrique et analysées en s’appuyant sur les propriétés thermiques obtenues par DSC et DMA. La résistivité volumique et la tenue diélectrique ont pu également être mesurées. Ces polyesters biodégradables sont comparés aux polymères conventionnels. / The declining resources of fossil fuels, increase in wide-spread pollution, emission of green-house gases and difficulties in recycling waste materials are pushing biodegradable polymers into prominence. In the domain of electrical engineering, many polymers find applications in various electrical insulation systems. These polymers are petro-based, not eco-friendly and most of them are not biodegradable. With an objective to replace conventional products, biodegradable polymers are explored for their dielectric properties.In this work, a detailed study on the present status in the research work on biodegradable polymers in the electrical engineering domain is presented. Thermal and electrical properties of both biodegradable and classical polymers are compiled and compared.The polymers processed and studied were Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), Polycaprolactone (PCL), Poly(lactic acid) (PLA) and PLA based nanocomposite. Dielectric properties for a wide range of temperature and frequency were measured by dielectric spectroscopy and analyzed with the help of DSC and DMA experiments. Volume resistivity and electrical breakdown were measured on few polymers. These biodegradable polyesters were compared with conventional polymers.

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Made available in DSpace on 2016-12-08T15:56:18Z (GMT). No. of bitstreams: 1 Jeol Stryhalski.pdf: 4312921 bytes, checksum: b338c848a830e15dee64928b0bf1545c (MD5) Previous issue date: 2015-08-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Titanium oxide films doped with niobium were deposited by sputtering, using triode magnetron sputtering technique. The Nb:TixOy films, as deposited, displays an interesting combination of properties: transparency and electrical conductivity. The sputtering of titanium and niobium was carried out from a titanium target with niobium inserts arranged in the erosion area. Films containing different ratios of [Nb/Ti], and deposited under different substrate bias, were characterized by the following techniques: atomic force microscopy; transmittance and reflectance measurements, Hall resistivity, x-ray diffraction (XRD), energy dispersive fluorescence of x-ray (EDX) and contact angle. It was not observed any peak of niobium oxide in the XRD pattern of Nb:TixOy, indicating that the Nb atoms are substitutional atoms in sites of Ti. Transmittance and reflectance measurements and simulations using the Tauc-Lorentz model allow us to obtain intrinsic optical properties such as refractive index and extinction coefficient. The transmittance depends on the percentage of niobium and type of substrate bias ( pulsed bias or DC bias ). Results of transmittance measurements of Nb:TixOy films (as deposited, without annealing) reached values up to 60%. Electrical resistivity measurements using the method of four points probe (ASTM F43-99) through van der Pauw technique indicate values around 10-2 Ωcm. The electrical properties were also calculated by using optical properties. It indicates a reduction in the resistivity due to the Nb incorporation and pulsed bias. The contact angle indicates that films deposited on glass substrates using pulsed bias and high content of Nb has smaller contact angles (high surface free energy). Another effect due to the Nb is the reduction of grain size (nano grains) and the production of smoother surface of the Nb:TixOy films. / Filmes de óxido de titânio dopados com nióbio foram obtidos através de pulverização catódica, utilizando o sistema Triodo Magnetron Sputtering. A pulverização catódica de titânio e nióbio foi feita a partir de um alvo de titânio com insertos de nióbio dispostos na zona de erosão. Filmes contendo diferentes proporções de [Nb/Ti], e depositados sob diferentes polarizações do substrato. Foram caracterizados pelas seguintes técnicas: microscopia de força atômica, medidas de transmitância e refletância, resistividade através de efeito Hall difração de raios X (DRX), espectroscopia de energia dispersiva por fluorescência de raios X (EDX) e ângulo de contato. Os resultados mostram que não há formação de óxido de nióbio, indicando que os átomos de Nb se alojam na estrutura do TixOy como átomos substitucionais nos sítios do Ti. Medidas de transmitância e refletância e simulações usando o modelo de Tauc-Lorentz permitiram a obtenção de propriedades óticas intrínsecas, como índice de refração e coeficiente de extinção. A transmitância depende do percentual de nióbio e do tipo de polarização do substrato (pulsado ou DC). A transmitância de filmes sem recozimento (na condição como depositado ) alcançam 60% na região do visível. A resistividade elétrica, medida pelo método de quatro pontas (norma ASTM F43-99) com a técnica de Van der Pauw, indicam valores da ordem de 10-2 Ωcm. As propriedades elétricas também foram calculadas por meio das propriedades óticas e indicam uma redução na resistividade com a presença de Nb e com a polarização pulsada. O ângulo de contato indica que filmes depositados com polarização pulsada e com maior concentração de Nb tem os menores ângulos de contato (maior energia livre de superfície). Outro efeito causado pela incorporação de Nb é a redução do tamanho de grão dos filmes e da nanorugosidade superficial dos filmes.

The PHD project has two main goals. The first one is specifically related to investigations on molecular dynamics, structural conformations and packing of polyfluorene-based polymers. For this purpose, Wide Angle X-Ray Diffraction (WAXD), Solid-State Nuclear Magnetic Resonance (NMR) and Dynamical-Mechanical Thermal Analysis (DMTA) are being used as the main techniques. The second goal is to correlate molecular phenomena, as characterized in the first part, with opto-electronic properties of polyfluorene when used as active layer in an electronic device, such as a Polymer Light-Emitting Diode (PLED). In the second part, fabrication of devices and their electrical characterization as a function of temperature are the main objectives. Impedance Spectroscopy, Current-Voltage characterization of the devices and Time-Of-Flight (TOF) techniques are among the main techniques to be used in the second part of the project. Therefore, the project combines fundamental studies on molecular dynamics with technological performance of organic electronic. / O projeto de doutorado entitulado \"Correlação das Propriedades Óticas e Elétricas com a Estrutura Física e Dinâmica Molecular de Filmes e Dispositivos de Polifluorenos e Derivados\". O primeiro é especificamente ligado a investigação da dinâmica molecular, conformação estrutural e empacotamento de polímeros derivados do polifluoreno. Para isso, Difração de Raio-X de Alto Ângulo (WAXD)1, Ressonânica Magnética no Estado Sólido (RMN) e Análise Térmica Dinâmico Mecânica (DMTA) serão utilizadas como técnicas principais. O segundo objetivo é o de correlacionar, os fenômenos observados na primeira parte do projeto, com as propriedades opto-eletrônicas dos filmes poliméricos sendo utilizados como camada ativa em dispositivos eletrônicos do tipo Diodo Polimérico Emissor de Luz (PLED). Na segunda parte, a fabricação dos dispositivos e sua caracterização como função da temperatura serão os principais objetivos. Espectroscopia de Impedância, Corrente-Voltagem, Tempo de Vôo (TOF) e Photo-CELIV serão as principais técnicas de caracterização utilizadas. Dessa forma, o projeto combina estudos fundamentais de aspectos moleculares com o desempenho tecnológico de dispositivos optoeletrônicos.

Apresentamos neste trabalho uma técnica alternativa para a obtenção de filmes finos de silício amorfo hidrogenado (&#945-Si:H). Nós depositamos &#945-Si:H em um sistema de deposição que utiliza descarga luminescente a baixas freqüências (60Hz). Para tanto, nós projetamos todo o reator para que este objetivo pudesse ser atingido. Os filmes obtidos por nós mostram propriedades ópticas e eletrônicas bastante próximas aquelas dos filmes produzidos pela técnica convencional de descarga luminescente a radiofreqüência (13,56 MHz). A temperatura do substrato ótima para a técnica de descarga luminescente a baixas freqüências está na faixa 150-170&#176C, em torno de 100&#176C menor do que aquela usada para radiofreqüência. Neste trabalho nós apresentamos medidas das propriedades dos filmes, incluindo condutividade no escuro, fotocondutividade, comprimento de difusão ambipolar, absorção no infra-vermelho, gap óptico, e densidade de defeitos de níveis profundos. Para realizar parte destas medidas, nós construímos sistemas experimentais de caracterização exclusivos para o &#945-Si:H. / In this work we present an alternative technique for producing hydrogenated amourphous silicon thin films (&#945-Si:H). We deposited &#945-Si:H in a low-frequency (60 Hz) glow-discharge deposition system. For this purpose, we designed completely the reactor. The films we produced show electronic and optical properties nearly equivalent to those of films prepared by the conventional radio-frequency (13,56 MHz) glow-discharge technique. The optimal substrate temperature for the low-frequency glow-discharge technique is 150-170&#176C, about 100&#176C lower than that radio-frequency. In this work, we report measurements of film properties, including dark conductivity, photoconductivity, ambipolar diffusion lenght, infrared absorption, optical band gap, and deep defect density. To do these measurements, we assembled experimental systems used to characterize &#945-Si:H.

A técnica de injeção de cargas por feixe eletrônico em materiais poliméricos pode ser utilizada como uma importante ferramenta no estudo das propriedades elétricas destes materiais. Fenômenos tais como a emissão eletrônica secundária, o transporte e armazenamento de portadores de carga no volume do material, fenômenos de injeção e condutividade induzida por radiação podem ser observados em películas finas de dielétricos lançando mão desta poderosa técnica. Neste trabalho, utilizamos um canhão de elétrons de energia variável (O a 10 keV) na irradiação de amostras de polianilinas, por nós sintetizadas, para o estudo da emissão secundária e de transporte no volume. Alguns experimentos foram também realizados com o poli(fluoreto de vinilideno), que é um polímero bem mais resistivo que as polianilinas. As medidas de emissão eletrônica foram feitas em circuito aberto, enquanto as medidas de transporte foram obtidas em circuito fechado. Neste segundo tipo de configuração, procuramos fazer uma análise do comportamento da corrente através da amostra pela observação de transientes rápidos (da ordem de 10 ms) de corrente gerados pela injeção de pacotes de carga de penetração bem definida a partir da superfície bombardeada. Propriedades elétricas intrínsecas como a condutividade do material e a permissividade elétrica, e extrínsecas como a condutividade na região irradiada foram utilizadas como parâmetros no ajuste dos resultados experimentais. / Charge injection in polymeric materials by electron beam is a powerful technique in the study of electrical properties of such materials. Secondary emission, transport and storage phenomena, as well as radiation-induced conductivity are among the subjects related to dielectrics that can be investigated. At present work we used an electron beam system (O to 10 keV) to irradiate polyaniline films, synthesized in our laboratory, and to perform studies of secondary emission and transport phenomena. Some experiments were also carried out with poly(viny1idene fluoride), a more resistivity polymer. Secondary emission measurements were carried out in an open-circuit configuration while the transport ones used a short circuit mode. Fast transient phenomena (about 10 ms) were also studied in details. Intrinsic electric properties, such as conductivity and dielectric constant, and extrinsic ones, like the induced conductivity in the irradiated region of the sample, were obtained in the fitting between the model and the experimental results.