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.

As células eletroquímicas emissoras de luz (PLECs) pertencem a um novo ramo importante na optoeletrônica orgânica devido ao seu grande potencial para ser usado como ponto - pixels para telas coloridas e também para painéis de iluminação. Diferentemente de diodos orgânicos emissores de luz (OLEDs), a tecnologia de OLECs ainda está em estágios iniciais de desenvolvimento, em comparação com a tecnologia de OLED , OLECs tem a vantagem de ser operado em ambas as polaridades de tensão ( para a frente ou de polarização reversa ), e, além disso, o seu desempenho é menos dependente dos materiais do eletrodos e a espessura da camada ativa do dispositivo. A camada ativa de um OLEC compreende uma mistura de um polímero eletroluminescente conjugado e um eletrólito de polímero. Consequentemente, o transporte elétrico durante a operação do dispositivo envolve uma combinação de dinâmica iônica e eletrônica e efeitos intrincados nas interfaces com os eletrodos. A literatura apresenta até agora duas abordagens diferentes para descrever o fenômeno de transporte nas OLECs. O modelo de eletrodinâmica, que combina separação iônica com o processo de difusão limitada eletrônica, e o modelo de dopagem eletroquímico que considera uma dopagem eletroquímica do polímero conjugado, dando a formação de uma junção p-i-n na camada ativa. Usando as medidas de decaimento da corrente sobre uma voltagem aplicada e espectroscopia de impedância /admissão , investigamos o transporte de portadores de carga em um OLEC tendo como camada ativa uma mistura de poli [ ( 9, 9 - dioctyl - 2, 7 - divinileno - fluorenileno ) - alt - co - { 2 - metoxi -5 - ( 2 - etil- hexiloxi ) -1,4 - fenileno } ] ( PFGE ) , com poli ( óxido de etileno ) ( PEO ) complexado com triflato de lítio ( TriLi ) , na proporção 01:01 : X , onde X foi de 0,10 , 0,05 , 0,01 , 0,00. Foram obtidos dados importantes relacionados com efeito iônico e eletrônico durante a operação deste PLEC, sendo que as medidas de transiente e de impedância mostraram que o movimento iônico auxilia o processo de injeção eletrônica. Outro fato relevante é que o desempenho da PLEC é dependente da formação da dupla camada iônica que tem sua espessura abaixo de 10 nm e que o processo de sua formação depende altamente da condução iônica, que por sua vez vai depender da quantidade de íons e de sua mobilidade, sendo influenciando por fatores como concentração de sal e temperatura do dispositivo. As medidas realizadas mostram que as PLECs com 2,5 e 5% de concentração de sal apresentam o melhor desempenho. / Organic Light-emitting Electrochemical Devices (OLECs) belong to a new important branch in organic optoelectronics due to their great potential to be used as dot-pixels for color displays and also to lighting panels. Differently from organic light-emitting diodes (OLEDs), the technology of OLECs is still in early stages of development. In comparison to OLED technology, OLECs have the advantage in being operated in both voltage polarities (forward or reverse bias), and, in addition, their performance is less dependent on the electrode materials and the device thickness. The active layer of an OLEC comprises a mixture of a conjugated electroluminescent polymer and a polymer electrolyte. Consequently, the electrical transport during the device operation involves a combination of ionic and electronic dynamics and intricate effects at the interfaces with the electrodes. The literature presents so far two different approaches to describe the transport phenomenon in the OLECs. The electrodynamic model, which combines ionic charge separation with electronic diffusionlimited process, and the electrochemical doping model that consider an electrochemical doping of the conjugated polymer, giving and the formation of a p-i-n junction in the active layer. Using current decay under an applied voltage measurements and impedance/admittance spectroscopy, we investigate charge carrier transport in an OLEC having as active layer a mixture of poly [(9, 9 - dioctyl - 2, 7 - divinileno - fluorenileno) - alt - co - {2 - methoxy -5 - (2 - ethyl-hexyloxy) -1,4 - phenylene}] (PFGE), with poly (ethylene oxide) (PEO) complexed with lithium triflate (TriLi), in the proportion 1:1:X, where X was 0.10, 0.05, 0.01, 0.00. We have obtained important results related to ionic and electronic effect during this operation PLEC. This measurements of transient current and impedance showed that ionic movement aids the process of electron injection. Another relevant fact is that the performance of PLEC is dependent on the formation of ionic double layer having thickness below 10 nm. The formation of this double layers is highly dependent on the ionic conduction, which in turn will depend on the amount of ions. The ionic mobility is influenced by factors such as salt concentration and temperature of the device. The measurements show that PLECS with 2.5 and 5% salt concentration had the best perform.

Les polysaccharides sont l'une des principales options à retenir pour progresser dans l'utilisation ou la conception de polymères renouvelables. Depuis les années cinquante, le développement industriel de ce type de polymères s'était considérablement réduit du fait de l'avènement des polymères synthétiques. Cependant, cet intérêt a cru considérablement ces dernières années en raison de la sensibilisation du public sur la limite des ressources fossiles. Ces biopolymères sont donc devenus un sujet d'importance, tant sur le plan industriel que sur celui de la recherche fondamentale. Toutefois, les systèmes à base de polysaccharides sont le plus souvent transformés via l'utilisation d'importantes quantités de solvants (y compris l'eau), ce qui globalement pénalise le procédé associé en l'affligeant d'une charge environnementale supplémentaire. Par la voie ‘fondue', le développement de polymères thermoplastiques à base de dérivés de la cellulose est un véritable défi, qui concerne autant le mode de transformation de ces systèmes que le niveau des propriétés du matériau final. Pour exemple, la température de dégradation de l'acétate de cellulose (CA) (dont le degré de substitution 2,5 est développé par le Groupe Solvay) est si proche de sa température de fusion que son procédé de mise en oeuvre ne peut être envisagé qu'avec l'ajout d'une quantité importante de plastifiants externes (entre 20 et 30 en poids selon le type d'additif). Le comportement d'un mélange CA-plastifiant est principalement régi par un «réseau» de très fortes interactions polaires, dont la force et la densité dépendent de 3 paramètres spécifiques: le degré de substitution de CA, la typologie de plastifiant et la quantité de plastifiant. Pour expliquer les différents mécanismes de plastification, il est donc important pour nous d'étudier et de comprendre les propriétés dynamiques (en ce qui concerne les phénomènes de relaxation) de ce type de systèmes et comment les trois leviers que nous avons identifiés peuvent influencer ou moduler les différentes interactions échangées dans les mélanges / Polysaccharides are one of the main options to the on-going move towards the use of renewable polymers. The industrial interest in this type of polymers drastically shrunk by the advent of synthetic polymers in the fifties, but is currently reviving due to the public awareness on the limit of fossil resources. These biopolymers are nowadays offering a challenging and industrially profitable playground for researchers. However, current polysaccharides based materials are mostly processed with extensive use of solvents (including water) making the total process an environmental burden despite the advantage of the starting material. Development of thermoplastic cellulose-based materials is very challenging regarding both final material properties and polymer processing. The degradation temperature of Cellulose Acetate (CA) (degree of substitution 2.5) is so close to its melting temperature that it can only be processed with a significant amount of external plasticizers (between 20 et 30 wt.% depending on the type of the additive). Behavior of a CA-plasticizer blend is mainly governed by a ‘network’ of high polar interactions, the strength and the density of which clearly depend of 3 specific parameters: the CA’s degree of substitution, the typology of the plasticizer, the amount of plasticizer. In an attempt to explain the different plasticization mechanisms, it is thus of utmost importance for us to study and understand the dynamic properties (regarding the relaxation phenomena) of this kind of systems and how the three levers that we identified can influence or modulate the different interactions exchanged within the blends

Submitted work deals with monitoring impact of thermal and electric ageing on the dielectric properties of insulating material NKN 0887. In the course of the experiment five sets of dielectric insulating materials were aged. The voltage range has been set from 1,5 kV till 2,2 kV and temperatures were 23 °C and 200 °C. The capacity and loss factor has been directly measured by RLC meter Agilent with attached electrode system. The electrode system operates on the principle of a plate capacitor. The values of relative permittivity and loss number has been calculated from values of capacity and loss factor. For easier confrontation has been frequency dependences of these values plotted in a chart. The Cole-Cole diagrams has been created and factors of Havriliak-Negami function has been calculated. Data has been compared with each other and the effect of ageing factors has been deduced.

Master´s thesis covers introduction to the problems of materials with specific proprieties named liquid crystals. Theoretic part features primary fission these materials, theirs mechanical, electrotechnical and optical characteristics. Interesting chapter is description choice application including perhaps most interesting using liquid crystals - liquid crystal display. In this trend continues experimental part too, where there are first mentioned characteristics LCD, and after it alone metering capacitive characteristics display with active matrix. Main attention in experiment is however concentraded on evaluation frequency analysis of components complex permittivity regarding in plant temperature on submitted sample liquid crystals.

The bachelor thesis submitted deals with properties of electro-insulating lacquer hardenable by ultraviolent radiation and temperature. Within the theoretical part a summary of electro-insulating lacquers used in electrotechnics has been elaborated. Chemical changes that take place in this material group have been described during hardening process. A method of dielectric relaxation spectroscopy specifically focused on mathematic and physical description of polarisation and conductive mechanisms taking place in the structure of the given material has been closely studied. In the experimental part a workplace for hardening and long-term exposition of lacquered samples during simultaneous effect of various climatic elements has been designed and built. The selected electric and mechanical properties have been monitored on three sets of experimental samples prepared by means of different methodical procedures. The results gained have been mathematically evaluated and physically interpreted in term of methodical procedure of hardening and different temperature of measurement.

Diploma thesis treat of effect of thermal, electrical and combined (thermal electrical) stress on electrical characteristics of insulation material ISONOM NMN which is used as a slot insulation in electric motors. To monitor the stress is used the method of dielectric relaxation spectroscopy. Under examinations are the resultant dielectric spectra which constitute the frequency dependencies of components of complex permitivity. Compared are the effects of particular stresses on dielectric spectra of surveyed insulative material.

This work deals with the studies of liquid oligobutadiens properties in AC electric field by dielectric relaxation spectroscopy method. The current issue in the diagnosis of oligomeric and polymeric materials during the activity of various degradation factors and options of their alleviation and suppression was studied. The existing apparatus is modified for monitoring possibilities of polymeric materials during the action of various degradation and operational factors. Effect of climatic factors are experimentally investigated, especially UV radiation and temperature on the course of the frequency dependence of complex permittivity components with respect to the different composition and length of the polymer chain.

Dielektrická relaxační spektroskopie je jednou z užitečných metod pro studium molekulární dynamiky materiálů. Díky nedávnému pokroku v přístrojové a měřicí technice je dnes možné získat dielektrické spektrum v širokém frekvenčním intervalu a pro velice rozdílné materiály. Cílem mé práce bylo studium dielektrických relaxačních spekter a vodivosti oxidů titanu, niobu, tantalu, lanthanu a hafnia pro katody pracující na principu studené emise. Cílem výzkumu bylo analyzovat frekvenční a teplotní chování těchto oxidů, včetně jejich vodivosti, v širokém frekvenčním a teplotním rozsahu, a pokusit se stanovit původ relaxačního mechanismu. Vzhledem k tomu, že původně zadaný rozsah oxidů byl dosti široký, soustředila se pozornost pouze na oxidy tantalu a niobu, rovněž s ohledem na jejich aplikace v elektrolytických kondenzátorech. Elektrické, tepelné a mechanické (při zpracování) vlastnosti oxidů tantalu a niobu jsou dnes již dobře prozkoumány. K dispozici je však jen málo poznatků o jejich dielektrických relaxačních mechanismech. Výsledky získané pro Ta2O5 ukazují existence relaxačního maxima, nacházejícího se v experimentálně dostupném teplotním a frekvenčním intervalu 187 K – 385 K a 1 Hz – 10 MHz. Frekvence ztrátového maxima se řídí Arrheniovým zákonem s aktivační energií 0.048 eV. Ve vodivostních spektrech vykazují tenké vrstvy Ta2O5 na nízkých frekvencích ustálenou hodnotu a při vysokých frekvencích monotónní nárůst, který závisí na teplotě. Pozorovanou vodivost lze popsat mocninnou funkcí s exponentem nepatrně větším než jedna (tzv. superlineární závislost). Výsledky získané pro Nb2O5 v podobné teplotní a frekvenční oblasti, 218 K – 373 K, 1 Hz – 1 MHz rovněž ukazují jedno relaxační maximum. Frekvence ztrátového maxima se opět řídí Arrheniovým zákonem s poněkud vyšší aktivační energií 0.055 eV. Niobové kondenzátory vykazují vodivostní mechanismus shodný s kondenzátory tantalovými.

In this work describe to the Dielectric relaxation spectroscopy for the evaluation of the actual status of insulation systém. The used methods of quantifying the dielectric response in time domain are polarization-depolarization current and recovery voltage measurement and in frequency domain the loss factor and the complex capacitance measurement. Influence of thermal ageing and temperature dependences of charge and dischage currents are observed.