Pesquisas e publicações sobre polímeros luminescentes vêm sendo desenvolvidas nos últimos anos devido à inovação acadêmica, porém ainda no âmbito nacional possuem aplicação industrial limitada. Marcadores ópticos processados são pouco explorados devido à dificuldade de processamento dos materiais poliméricos luminescentes com estabilidade de luminescência. Os materiais utilizados para o processamento de polipropileno luminescente foram Poliamida 6 (PA6) dopada com complexo sintetizado de [Eu(tta)3(H2O)2] obtida através do processo de diluição do polímero e técnica de derramamento. As poliolefinas, por serem inertes, não se adequam ao procedimento comum de dopagem, assim no presente trabalho, o polipropileno luminescente foi preparado indiretamente por dopagem com poliamida dopada com complexo de európio em processamento por extrusão. As técnicas de caracterização utilizadas foram a Análise Térmica (TG), Calorimetria Exploratória Diferencial (DSC), Difração de Raios-X (XRD), Espectroscopia de infravermelho (FT-IR) e estudo das propriedades fotoluminescentes. A blenda PP/PA6:Eu(tta)3 processada apresentou propriedades luminescentes observadas nas transições intraconfiguracionais de bandas finas 4f6 - 4f6 relativas aos níveis de excitação de energia 7F0 → 5L6 (394nm), 7F0 → 5D3 (415nm), 7F0 → 5D2 (464nm), 7F0 → 5D1 (525nm) e 7F0 → 5D0 (578nm). Tanto a blenda de PP/PA6:Eu(tta)3 e os filmes de PA6:Eu(tta)3 quando expostos a luz UV (365nm) apresentaram luminescência vermelha. Os resultados de TG mostraram que sob atmosfera de O2 o PP dopado PA6:Eu(tta)3 apresentou maior estabilidade do que o PP puro. Neste trabalho foi possível processar PP/PA6:Eu(tta)3 com propriedades térmicas e fotoestabilidade, que permitem sua utilização com marcador óptico em processamentos. / Research and publications about luminescent polymers have been developed in the last years for the academic innovation; however the industrial application has been very limited in this area. Processed Optical markers are few explored due to the difficult to process luminescent polymeric materials with stable luminescence. The materials used of processing luminescent polypropylene (PP) were polyamide 6 (PA6) doped with europium complex [Eu(tta)3(H2O)2] obtained through the dilution and casting process. Due to their inercy, polyolefins do not fit into the common procedure of doping, in consequence, in this work luminescent polypropylene was indirectly prepared by polyamide 6 doped with europium complex through extrusion process. Product characterization was done using Thermalgravimetry analysis (TG), Differential Scanning Calorimetric (DSC), X-Ray Diffraction (XRD), Infrared spectroscopy (FTIR) and fotoluminescence of emission and excitation. The blend PP/PA6:Eu(tta)3 presented luminescent properties, after semi-industrial process, as observed in the narrow bands of intraconfiguration transitions - 4f6 relatives to energy levels 7F0 → 5L6 (394nm), 7F0 → 5D3 (415nm), 7F0 → 5D2 (464nm), 7F0 → 5D1 (525nm) e 7F0 → 5D0 (578nm) of emission spectrum. Red light of the pellets or film is emitted when excited in UV lamp (365nm). TG results showed under O2 atmosphere that PP doped with PA6:Eu(tta)3 was more stable than pure PP. In this work luminescent PP/PA6:Eu(tta)3 was processed with properties of thermal and photo stability which can be used as optical marker in polymer processing.

Este trabalho objetivou a caracterização mecânica e a análise de falha de dois tipos de juntas compósitas através de ensaios mecânicos, em que uma das juntas era composta por dois laminados de fibras de carbono recoberto em ambas as faces por tecido de fibra de vidro reforçando uma matriz termoplástica (PPS-C) unidos via soldagem por resistência elétrica, e a outra confeccionada com dois laminados de fibras de carbono reforçando uma matriz de resina epóxi (EPX-C) unidos via colagem por filme de resina epoxídica. Os dois tipos de juntas foram submetidos a impacto único transversal de 10 J, condicionamento higrotérmico, além de carregamento em fadiga compressiva no plano nas mais diversas combinações destes processos degradativos de suas propriedades mecânicas. Observou-se, que a junta termorrígida colada de EPX-C apresentou a maior resistência mecânica em flexão em quatro pontos (F4P) na condição original (como-manufaturada), assim como os maiores valores de resistência residual para as várias condições de degradação mecânica e higrotérmica a que foi submetida. Por sua vez, a junta termoplástica soldada de PPS-C exibiu, em termos percentuais, menores reduções dos valores de resistência à flexão sob as condições avaliadas, relativamente às perdas apresentadas pela junta EPX-C em idênticas circunstâncias. A análise macroscópica da superfície de fratura de ambas as juntas indicou que o modo de falha predominante da junta termorrígida foi interfacial enquanto que, para a junta PPS-C, o modo de falha predominante foi o intralaminar. Análises fratográficas através da microscopia eletrônica de varredura (MEV) evidenciaram para a junta termorrígida EPX-C, uma alta adesão entre fibra/matriz, porém uma relativamente fraca interação entre os aderentes (laminado) e o filme adesivo de colagem, enquanto que, para a junta termoplástica PPS-C, reduzidas interações fibra/matriz forem inferidas na camada externa de PPS-V do aderente assim como entre a malha metálica resistiva e os filmes puros de PPS que a revestiam. Em ensaios de resistência ao cisalhamento interlaminar (ILSS), os espécimes retirados da junta EPX-C na condição virgem evidenciaram uma colagem uniforme/homogênea, enquanto que, para a junta PPS-C, os espécimes de ensaio usinados a partir da junta virgem indicaram a ocorrência de efeitos de degradação térmica altamente localizada nas bordas soldadas. / This study aimed to mechanical characterization and failure analysis of two kinds of composite single-lap joints by mechanical tests, in which a single-lap joint was made of two adherents of carbon fibers coated on both sides with glass fiber fabric reinforcing a thermoplastic matrix (PPS-C) welded via resistance welding, and the another type made of two adherents of carbon fibers reinforcing an epoxy matrix (EPX-C) bonded by epoxy adhesive film. The two types of single-lap joints were subjected to single transverse impact of 10 J, hygrothermal conditioning, and compressive fatigue loading in the plane in various combinations of these degradative processes of mechanical properties. It was observed that the thermosetting bonded joint EPX-C showed the highest strength in four point-flexure test in the original condition (as-manufactured), as well as greater residual strength values for the various conditions of mechanical and hygrothermal degradation which was subjected. In turn, the welded thermoplastic joint PPS-C exhibited, in percentage terms, smaller reductions in flexural strength values under the tested conditions, in respect of losses showed by EPX-C in similar circumstances. Macroscopic analysis of the fracture surfaces from both joints indicated that the predominant failure mode was interfacial to thermosetting while for PPS-C joint, the predominant failure mode was intralaminar. Analysis of fracture surfaces by scanning electron microscopy (SEM) showed, for thermosetting joints EPX-C, a high adhesion between fiber/matrix, but a relatively weak interaction between adherents and the bonding adhesive film, whereas for thermoplastic joint PPS-C, reduced interactions fiber/matrix are inferred in the outer layers of PPS-V and between metal mesh and the pure PPS films that coated it. In the interlaminar shear strength tests (ILSS), the specimens removed from the EPX-C joint in the pristine condition showed a uniform/homogeneous bonding along the joint area, while for PPS-C joint, coupons extracted from pristine condition joint indicated the occurrence of degradation caused by thermal effects localized in the welded edges.

La thèse est consacrée aux matériaux électro-actifs, qui sont développés et conçus pour faire de la conversion entre énergie électrique et énergie mécanique. Avec les nouvelles technologies émergentes de transduction électromécanique, les polymères électro-actifs (EAP) ont gagné une attention considérable. Ils présentent de grandes déformations quand ils sont soumis à un champ électrique. Cependant, ces matériaux présentent de faibles permittivités et exigent pour fonctionner l’application de forts champs électriques. Les recherches entreprises dans la thèse traitent de différentes méthodes ayant pour but d'augmenter la permittivité des polymères et par conséquent d’améliorer les propriétés électromécaniques sous des champs électriques modérés. Les différentes approches consistent à la mise au point de nouveaux matériaux, par la méthode de mélange de polymères ou en utilisant un nouveau type de polymère, et par l'incorporation de nano-charges spéciales dans la matrice polymère. Un mélange de polyuréthane (PU) et PEMG obtenu à partir d'un procédé en solution conduit à des valeurs plus basses de module de Young, mais aussi à de plus faibles permittivités diélectriques. Il est cependant mis en évidence une amélioration des propriétés électromécaniques, par exemple, à le gain à des champs électriques modérés est d’un facteur 2, avec seulement 9% en poids de PEMG. Deux types de Pebax sont testés comme matrice polymère. Des valeurs très élevées de permittivités sont obtenus plus particulièrement pour le Pebax1657 mais liés pour ce matériau à des valeurs élevées de conductivité. En dépit de ces permittivités élevées, seule une légère amélioration de la conversion électromécanique est observée par rapport au polyurethane. Nous nous sommes également intéressés aux nanocomposites de polyuréthane basés sur desnanoparticules d'argent recouvertes de polymère polyvinylpyrrolidone (PVP). Un fin revêtement de polymère sur les nanoparticules d'argent conduit à une meilleure dispersion des charges dans les films de polyuréthane, et des valeurs plus élevées de permittivité. Différentes quantités d'Ag-PVP sont testées jusqu'au seuil de percolation proche de 45% en poids de charges. À partir des mesures par interférométrie laser et du nouveau dispositif de caractérisation croisée, les propriétés électromécaniques optimales sont obtenues pour 20% en poids de Ag-PVP, avecun gain de 2 à 6 par rapport au polyuréthane pur. Afin d'expliquer la différence entre les résultats expérimentaux et attendus, et par conséquent pour parvenir à une meilleure compréhension du comportement électromécanique de ces différents matériaux, certaines hypothèses ont été discutées et testées. Nous avons montré notamment une baisse des permittivités diélectriques sous champs électriques pour les Pebax et les nanocomposites, des problèmes d'absorption d'eau pour les Pebax et une diminution de cristallinité dans le cas des nanocomposites PU-Ag. / The thesis is devoted to electroactive materials, which are developed and designed to make conversion between the electricity and the mechanical form. With newer emerging electromechanical transduction technologies, electroactive polymers (EAP) have gained a considerable attention. The polymers are competitive in many applications such as actuators, sensors, robotic system and biological mimics since they are cheap, light, easy to process, and they present large electric field-induced strains. However, these materials suffer from the low permittivity and high voltage requirement to drive the actuations. The research undertaken for the thesis intends then to provide different methods in order to enhance the polymer permittivity and consequently the electromechanical activities at moderate electric fields. The different approaches consist on the development of new materials by polymer blend method or by using new kind of polymer, and on the incorporation of special nano-fillers in the polymer matrix. A blend of polyurethane (PU) and poly [ethylene-co-(methyl acrylate)-co-(glycidyl methacrylate) (PEMG) obtained from a simple solution method leads to lower values of Young modulus but also lower dielectric permittivities. The PU-PEMG blend presents however an improvement of the electromechanical capabilities, for example it is obtained a two fold increase of the strain at moderate fields with only 9%wt of PEMG.Two types of Polyetherblockamide (Pebax) are tested as polymer matrix. Very high values of permittivities are obtained particulary for Pebax1657 but accompanied for this material by high values of conductivity. Despite these high permittivities (more than 200000 for Pebax 1657 and 500 for Pebax 2533 at 0.1 Hz), only a moderate improvement of the electromechanical capability is observed compared to PU. We are also intererested on polyurethane nanocomposites based on silver nanoparticles coverered by PolyVinylPyrrolidone (PVP) polymer. A little polymer coating of the nanosilver leads to a better dispersion into the polyurethane films and higher values of permittivity. Different amounts of Ag-PVP are tested up to the percolation threshold close to 45%wt of fillers. Based on laser interferometer measurements and new cross characterization device, the optimal electromechanical properties are obtained for 20 %wt of Ag-PVP and a gain of 2 to 6 is obtained compared to pure polyurethane. In order to explain the difference between experimental and expected results and consequently to achieve a better understanding of the electromechanical behaviour of these different materials, some hypotheses were discussed and tested. We have shown particularly a drop of dielectric permittivities under electric fields for Pebax and nanocomposites, some problems of water absorption for Pebax and a decrease of crystallinity for the PU-Ag nanocomposites.

Este trabalho apresenta a preparação, caracterização e estudos sobre as propriedades de fotoluminescência dos complexos de coordenação a partir de β-dicetonatos e salicilatos de terras raras trivalentes (βdicetonatos = acac- e tta-; salicilatos = Hsal- e TR3+ = Sm3+, Eu3+, Gd 3+e Tb3+) dopados nos polímeros PHB (poli3hidroxibutirato) e PMMA (polimetilmetacrilato). Os sistemas poliméricos foram caracterizados por meio das técnicas de microanálises de CHN, titulação complexométrica com EDTA, espectroscopia de absorção na região do infravermelho, análises termogravimétricas TGA/DTG e difratometria de raios X (método do pó). Os dados de espectroscopia no IV evidenciaram a ocorrência da interação entre as matrizes poliméricas PHB e PMMA com os complexos de β-dicetonatos e salicilatos de TR.3+ As análises termogravimétricas TGA/DTG sugeriram o caráter anidro na maioria dos sistemas poliméricos dopados e apresentaram uma diminuição de termoestabilidade com o aumento da dopagem. Os difratogramas de raios X evidenciaram que os filmes poliméricos são semicristalinos e que cada uma das séries apresenta perfis espectrais semelhantes. A cristalinidade dos sistemas aumentou em função da porcentagem de dopagem e, ao mesmo tempo, mantémse independente da variação do íon TR3+ ou ligante de coordenação. Foram observados nos espectros de excitação dos complexos de TR3+ dopados nos polímeros PHB e PMMA supressão de luminescência das bandas finas oriundas das transições 4f4f proveniente dos íons TR3+. Os espectros de emissão dos sistemas PHB e PMMA dopados com os complexos de Gd3+, utilizadas técnicas do estado estacionário e resolvido no tempo, evidenciaram que os estados tripletos T do ligante tta mostraramse mais ressonantes com os níveis excitados 5D0 do íon Eu3+ e 4G5/2 do Sm3+. Por outro lado, os estados T dos ligantes acac e Hsal estão mais ressonantes com o nível emissor 5D4 do íon Tb.3+ Com base nos espectros de emissão dos sistemas PHB e PMMA dopados com complexos de Sm3+, Eu3+ e Tb3+ apresentaramse bandas características das transições intraconfiguracionais oriundas dos íons Sm3+ (4G5/2→6H5/2→11/2), Eu3+ (5D0→7FJ, J = 0—6) e Tb3+ (5D0→7FJ, J = 0—6) exibindo cores de emissões vermelhaalaranjada, vermelha e verde, respectivamente. Para a maioria dos filmes dopados houve supressão de luminescência em função do aumento da concentração da dopagem. As propriedades fotoluminescentes foram investigadas a partir dos dados espectrais dos sistemas PHB e PMMA dopados com complexos hidratados que mostraram, principalmente, bandas finas oriundas das transições 5D0&#85947F0—4 (Eu3+), dominados pela transição hipersensível 5D0—7F2 (~612 nm) indicando que íon Eu3+ encontrase em um ambiente químico não centrossimétrico. Os filmes PHB:Eu(tta)3 e PMMA:Eu(tta)3 apresentaram maiores valores de Ω2, sugerindo que o íon Eu3+ localizase em um ambiente químico mais polarizável. Os maiores valores de eficiência quântica de emissão do nível emissor 5D0 (η) foram para os filmes poliméricos dopados com o complexo [Eu(tta)3(H2O)2]. As cores das emissões dos sistemas poliméricos sintetizados neste trabalho possibilitam aplicações em sistemas tricolor, visto que suas emissões correspondem às cores primárias vermelho (Eu3+), azul (Gd3+) e verde (Tb3+). Os filmes PMMA:Gd(Hsal)3, apresentaram altas intensidades de emissão oriundas das transições T1→S0 do ligante salicilato, emitindo cor azul a temperatura ambiente (298 K). As matrizes poliméricas desempenham papéis essenciais nos processos de sensibilização luminescente dos sistemas contendo Eu3+ e Tb3+ e, portanto, atuam como Dispositivos Moleculares Conversores de Luz (DMCLs) / This work presents the preparation, characterization and studies of photoluminescence properties based on trivalent rare earth coordination complexes of βdiketonates and salicylates (β-diketonates = acac- and tta-; salicylates = Hsal- and RE3+ = Sm3+, Eu3+, Gd3+ and Tb3+) doped into polymers PHB (poly3hydroxybutyrate) and PMMA (polymethylmethacrylate). The polymer systems were characterized using techniques of CHN microanalysis, complexometric titration with EDTA, infrared absorption spectroscopy, thermogravimetric analysis TGA/DTG and Xray powder diffraction. Data from the IR spectroscopy revealed the occurrence of interaction between the PHB and PMMA polymer matrix with the RE3+ complex of βdiketonates and salicylates. The thermogravimetric analysis TGA/DTG suggested anhydrous character in most doped polymer systems and showed a decrease of thermal stability with increasing doping content. The Xray diffraction study showed that the polymer films are semicrystalline and each series presents spectral profiles similar to each other. The crystallinity of the polymeric systems increased according to the doping percentage and, at the same time, maintained independent to the alteration of RE3+ ion or the coordinated ligand. It was observed in the excitation spectra of PHB and PMMA polymer systems doped with RE3+-complexes luminescence quenching of narrow bands arising from the 4f4f transitions of RE3+ ions. In the emission spectra of PHB and PMMA systems doped with Sm3+, Eu3+ and Tb3+ complexes, characteristic emission bands arising from intraconfigurational transitions were observed from the ions Sm3+ (4G5/2→6H5/2,-11/2), Eu3+ (5D0→7FJ, J = 0-6) and Tb3+ (5D4→7FJ, J = 6-0), exhibiting orangered, red and green colour emission, respectively. Most of the doped films displayed concentration quenching of luminescence. Photoluminescence properties were investigated based on the spectroscopic data obtained for systems of PHB and PMMA doped with hydrated complexes. Particularly, emission bands arising from the 5D0→7F0-4 transitions (Eu3+) were dominated by the hypersensitive 5D07F2 transition (~612 nm), indicating that the Eu3+ ion is found in a noncentrosymmetric chemical environment. PHB:Eu(tta)3 and PMMA:Eu(tta)3 films showed high Ω2 values, suggesting that the Eu3+ ion is located in a more polarizable chemical environment. The highest values of emission quantum efficiency (η) of the 5D0 emitting level were found with those polymer films doped with [Eu(tta)3(H2O)2] complex. The emission colours of polymer systems synthesized in this work enabled their potential applications in fullcolour displays, since their emissions are the primary colours: red (Eu3+), blue (Gd3+) and green (Tb3+). The PMMA:Gd(Hsal)3 films exhibits intense blue colour emission arising from the T1→S0 transition of the salicylate ligand at room temperature (298 K). The polymer matrix performs an essential role in the luminescent sensitization processes for systems containing Sm3+, Eu3+, Gd3+ and Tb3+, hence the overall systems act as Light Conversion Molecular Devices (LCMDs)

Este trabalho apresenta a preparação, caracterização e estudos sobre as propriedades de fotoluminescência dos complexos de coordenação a partir de β-dicetonatos e salicilatos de terras raras trivalentes (βdicetonatos = acac- e tta-; salicilatos = Hsal- e TR3+ = Sm3+, Eu3+, Gd 3+e Tb3+) dopados nos polímeros PHB (poli3hidroxibutirato) e PMMA (polimetilmetacrilato). Os sistemas poliméricos foram caracterizados por meio das técnicas de microanálises de CHN, titulação complexométrica com EDTA, espectroscopia de absorção na região do infravermelho, análises termogravimétricas TGA/DTG e difratometria de raios X (método do pó). Os dados de espectroscopia no IV evidenciaram a ocorrência da interação entre as matrizes poliméricas PHB e PMMA com os complexos de β-dicetonatos e salicilatos de TR.3+ As análises termogravimétricas TGA/DTG sugeriram o caráter anidro na maioria dos sistemas poliméricos dopados e apresentaram uma diminuição de termoestabilidade com o aumento da dopagem. Os difratogramas de raios X evidenciaram que os filmes poliméricos são semicristalinos e que cada uma das séries apresenta perfis espectrais semelhantes. A cristalinidade dos sistemas aumentou em função da porcentagem de dopagem e, ao mesmo tempo, mantémse independente da variação do íon TR3+ ou ligante de coordenação. Foram observados nos espectros de excitação dos complexos de TR3+ dopados nos polímeros PHB e PMMA supressão de luminescência das bandas finas oriundas das transições 4f4f proveniente dos íons TR3+. Os espectros de emissão dos sistemas PHB e PMMA dopados com os complexos de Gd3+, utilizadas técnicas do estado estacionário e resolvido no tempo, evidenciaram que os estados tripletos T do ligante tta mostraramse mais ressonantes com os níveis excitados 5D0 do íon Eu3+ e 4G5/2 do Sm3+. Por outro lado, os estados T dos ligantes acac e Hsal estão mais ressonantes com o nível emissor 5D4 do íon Tb.3+ Com base nos espectros de emissão dos sistemas PHB e PMMA dopados com complexos de Sm3+, Eu3+ e Tb3+ apresentaramse bandas características das transições intraconfiguracionais oriundas dos íons Sm3+ (4G5/2→6H5/2→11/2), Eu3+ (5D0→7FJ, J = 0—6) e Tb3+ (5D0→7FJ, J = 0—6) exibindo cores de emissões vermelhaalaranjada, vermelha e verde, respectivamente. Para a maioria dos filmes dopados houve supressão de luminescência em função do aumento da concentração da dopagem. As propriedades fotoluminescentes foram investigadas a partir dos dados espectrais dos sistemas PHB e PMMA dopados com complexos hidratados que mostraram, principalmente, bandas finas oriundas das transições 5D0&#85947F0—4 (Eu3+), dominados pela transição hipersensível 5D0—7F2 (~612 nm) indicando que íon Eu3+ encontrase em um ambiente químico não centrossimétrico. Os filmes PHB:Eu(tta)3 e PMMA:Eu(tta)3 apresentaram maiores valores de Ω2, sugerindo que o íon Eu3+ localizase em um ambiente químico mais polarizável. Os maiores valores de eficiência quântica de emissão do nível emissor 5D0 (η) foram para os filmes poliméricos dopados com o complexo [Eu(tta)3(H2O)2]. As cores das emissões dos sistemas poliméricos sintetizados neste trabalho possibilitam aplicações em sistemas tricolor, visto que suas emissões correspondem às cores primárias vermelho (Eu3+), azul (Gd3+) e verde (Tb3+). Os filmes PMMA:Gd(Hsal)3, apresentaram altas intensidades de emissão oriundas das transições T1→S0 do ligante salicilato, emitindo cor azul a temperatura ambiente (298 K). As matrizes poliméricas desempenham papéis essenciais nos processos de sensibilização luminescente dos sistemas contendo Eu3+ e Tb3+ e, portanto, atuam como Dispositivos Moleculares Conversores de Luz (DMCLs) / This work presents the preparation, characterization and studies of photoluminescence properties based on trivalent rare earth coordination complexes of βdiketonates and salicylates (β-diketonates = acac- and tta-; salicylates = Hsal- and RE3+ = Sm3+, Eu3+, Gd3+ and Tb3+) doped into polymers PHB (poly3hydroxybutyrate) and PMMA (polymethylmethacrylate). The polymer systems were characterized using techniques of CHN microanalysis, complexometric titration with EDTA, infrared absorption spectroscopy, thermogravimetric analysis TGA/DTG and Xray powder diffraction. Data from the IR spectroscopy revealed the occurrence of interaction between the PHB and PMMA polymer matrix with the RE3+ complex of βdiketonates and salicylates. The thermogravimetric analysis TGA/DTG suggested anhydrous character in most doped polymer systems and showed a decrease of thermal stability with increasing doping content. The Xray diffraction study showed that the polymer films are semicrystalline and each series presents spectral profiles similar to each other. The crystallinity of the polymeric systems increased according to the doping percentage and, at the same time, maintained independent to the alteration of RE3+ ion or the coordinated ligand. It was observed in the excitation spectra of PHB and PMMA polymer systems doped with RE3+-complexes luminescence quenching of narrow bands arising from the 4f4f transitions of RE3+ ions. In the emission spectra of PHB and PMMA systems doped with Sm3+, Eu3+ and Tb3+ complexes, characteristic emission bands arising from intraconfigurational transitions were observed from the ions Sm3+ (4G5/2→6H5/2,-11/2), Eu3+ (5D0→7FJ, J = 0-6) and Tb3+ (5D4→7FJ, J = 6-0), exhibiting orangered, red and green colour emission, respectively. Most of the doped films displayed concentration quenching of luminescence. Photoluminescence properties were investigated based on the spectroscopic data obtained for systems of PHB and PMMA doped with hydrated complexes. Particularly, emission bands arising from the 5D0→7F0-4 transitions (Eu3+) were dominated by the hypersensitive 5D07F2 transition (~612 nm), indicating that the Eu3+ ion is found in a noncentrosymmetric chemical environment. PHB:Eu(tta)3 and PMMA:Eu(tta)3 films showed high Ω2 values, suggesting that the Eu3+ ion is located in a more polarizable chemical environment. The highest values of emission quantum efficiency (η) of the 5D0 emitting level were found with those polymer films doped with [Eu(tta)3(H2O)2] complex. The emission colours of polymer systems synthesized in this work enabled their potential applications in fullcolour displays, since their emissions are the primary colours: red (Eu3+), blue (Gd3+) and green (Tb3+). The PMMA:Gd(Hsal)3 films exhibits intense blue colour emission arising from the T1→S0 transition of the salicylate ligand at room temperature (298 K). The polymer matrix performs an essential role in the luminescent sensitization processes for systems containing Sm3+, Eu3+, Gd3+ and Tb3+, hence the overall systems act as Light Conversion Molecular Devices (LCMDs)

Σύνθετα που ενσωματώνουν σιδηροηλεκτρικά και πιεζοηλεκτρικά νανοσωματίδια, ομοιογενώς διεσπαρμένα μέσα σε μήτρα άμορφου πολυμερούς, αντιπροσωπεύουν μια νέα κατηγορία υλικών. Τα νανοδιηλεκτρικά σύνθετα ανήκουν σε ένα νέο τύπο υλικών που παρασκευάζονται για βελτιωμένες επιδόσεις, σαν διηλεκτρικά και ηλεκτρικοί μονωτές. Ορισμένα κεραμικά υλικά μπορούν να επιλεγούν και να αναμιχθούν με πολυμερή για να επιτευχθεί συνέργια μεταξύ της υψηλής διηλεκτρικής αντοχής των πολυμερών και της υψηλή διηλεκτρικής σταθεράς των κεραμικών. Τα εν λόγω συστήματα μπορούν να χρησιμοποιηθούν σε πολλές εφαρμογές, όπως σε ολοκληρωμένους πυκνωτές αποσύζευξης, ακουστικούς αισθητήρες εκπομπής, επιταχυνσιόμετρα γωνιακής επιτάχυνσης και ελεγκτές ρεύματος διαρροής, καθώς και σε στρατιωτικούς εξοπλισμούς και εφαρμογές στις μεταφορές. Έχει διαπιστωθεί πως τα νανοσύνθετα παρουσιάζουν βελτιωμένες ιδιότητες, αλλά όχι πλήρως κατανοητές, συγκριτικά με τα μικροσύνθετα. Επιπλέον, μελέτες δείχνουν ενδιαφέρουσες συμπεριφορές, όταν πρόκειται για πολύ χαμηλές περιεκτικότητες σε νανοσωματίδια. Στην παρούσα μελέτη, νανοσύνθετα εποξειδικής ρητίνης και κεραμικών νανοσωματιδίων BaSrTiO3 (μεικτό οξείδιο τιτανικού στροντίου βαρίου, BST) (<100 nm), παρασκευάστηκαν με διαδικασία ανάμειξης σε ένα ευρύ φάσμα συγκεντρώσεων, με σκοπό να μελετηθεί η επίδραση της πολύ χαμηλής (ή πολύ υψηλής) περιεκτικότητας στα χαρακτηριστικά του συστήματος. Οι διηλεκτρικές ιδιότητες και τα φαινόμενα χαλάρωσης μελετήθηκαν με τη βοήθεια της διηλεκτρικής φασματοσκοπίας (BDS) στο εύρος θερμοκρασιών από 30 oC έως 160 oC και συχνοτήτων 10-1 Hz έως 107 Hz. Ο μορφολογικός χαρακτηρισμός έγινε μέσω της ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) και διαπιστώθηκε πως η νανοδιασπορά των εγκλεισμάτων είναι επιτυχής. Ο δομικός χαρακτηρισμός, των δοκιμίων αλλά και των σωματιδίων BaSrTiO3, έγινε μέσω περίθλασης ακτίνων-Χ (XRD) και διαπιστώθηκε πως τα φάσματα έρχονται σε συμφωνία με τη σχετική βιβλιογραφία. Από την ανάλυση των αποτελεσμάτων της διηλεκτρικής φασματοσκοπίας καταγράφονται τρεις διηλεκτρικές χαλαρώσεις, που αποδίδονται με φθίνουσα σειρά των χρόνων χαλάρωσης, στη διεπιφανειακή πόλωση, την μετάπτωση από την υαλώδη στην ελαστομερική φάση της μήτρας (α-χαλάρωση) και σε επαναδιευθετήσεις πολικών πλευρικών ομάδων της κύριας πολυμερικής αλυσίδας (β-χαλάρωση). Η εξέταση της επίδρασης της περιεκτικότητας σε νανοεγκλέισματα, στη διηλεκτρική απόκριση των σύνθετων αποκαλύπτει μη-αναμενόμενες συμπεριφορές, σε χαμηλές (αλλά και υψηλές) περιεκτικότητες. Πιο συγκεκριμένα στις χαμηλές περιεκτικότητες εμφανίζονται φαινόμενα ακινητοποίησης των μακροαλυσίδων και επακόλουθα των διπόλων, με αποτέλεσμα τη μείωση της διαπερατότητας και την αύξηση της θερμοκρασίας υαλώδους μετάπτωσης του συστήματος. Αντίστοιχα σε υψηλές περιεκτικότητες υπάρχει εκ νέου αύξηση της θερμοκρασίας υαλώδους μετάπτωσης, λόγω περιορισμένης κινητικότητας των διπόλων. Συμπερασματικά, θεωρείται πως υπάρχουν τρεις ‘’ζώνες περιεκτικοτήτων’’ που προσδίδουν διαφορετικά χαρακτηριστικά στη διηλεκτρική συμπεριφορά του συστήματος, μέσω της ρύθμισης των αλληλεπιδράσεων ρητίνης-εγκλεισμάτων. / Ceramic–polymer composites incorporating ferroelectric and piezoelectric crystal nanoparticles, homogeneously dispersed within an amorphous polymer matrix represent a novel class of materials. Nanodielectric composites belong to a new type of engineering materials suitable for improved performance as dielectrics and electrical insulators. Certain ceramic materials can be selected to be blended with polymers providing synergy between the high breakdown strength of polymers and the high permittivity of ceramic materials. These type of material systems can be used in plenty applications such as integrated decoupling capacitors, acoustic emission sensors, angular acceleration accelerometers, smart skins and leakage current controllers, as well as in military equipment and transport applications. It has been found that nanocomposites exhibit enhanced properties, yet not fully understandable, comparably to microcomposites. Furthermore, literature demonstrates some interesting dielectric behaviors when filler’s concentration comes to very low nanoparticle loadings. In the present study, nanocomposites of epoxy resin and ceramic BaSrTiO3 (Barium-Strontium Titanate, BST) nanoparticles (<100 nm), were prepared with a mixing procedure in a wide range of nanofiller concentrations, aiming to investigate the impact of very low (or very high) loadings on the system’s properties. The dielectric properties and the related relaxation phenomena were studied by means of Broadband Dielectric Spectroscopy (BDS) in the temperature range from 30 oC to 160 oC and frequency range from 10-1 Hz to 107 Hz. Scanning electron microscopy (SEM) was employed in order to examine the morphology of the produced specimens. The dispersion of nanoinclusions can be considered as satisfactory. Structural characterization of the systems as well as of the BaSrTiO3 nanopowder was examined via x-ray diffraction (XRD). Obtained results are in accordance with literature. Three dielectric relaxation processes were detected form the analysis of the dielectric spectra. They are attributed, with descending order of relaxation time, to interfacial polarization, glass to rubber transition of the polymer matrix (α-relaxation), and re-arrangement of polar side groups of the main macromolecular chain (β-relaxation). The influence of the nanoparticles content upon the dielectric response of the composites, reveal unexpected behaviours at low and high filler loading. In particular, effects of immobilization/entanglement of macromolecular chains and subsequently of dipoles, resulting to a decrease of the permittivity values and enhancement of the glass to rubber transition temperature of the systems, were ascertained. At the opposite edge, at high filler loading, an increase of glass to rubber transition temperature was also found, due to the limited mobility of the chains and dipoles. Concluding, the existence of three “zones of filler content” is assumed, providing different characteristics in the dielectric response of the systems, because of the tunable polymer-inclusion interactions.

This work is generally aimed to synthesize POSS based BCPs via RAFT polymerization, to study their self-assembly behaviors, to research on the effect of POSS self-assembly structure on the bulk properties and to prepare nanostructured hybrid epoxy via self-assembly of POSS based copolymer. In Chapter1, We studied the RAFT polymerization of POSS macromers and capable to synthesize well defined POSS based BCPs with high POSS fraction and different topology such as AB，BAB and (BA)3. The vertex group and the morphology effect on thermo-mechanical properties of POSS based BCPs as well as the structure-property relationship was investigated. Dispersion RAFT polymerization in apolar solvent was applied and various aggregates with different morphology in Chapter2. Cooling induced reversible micelle formation and transition was found and the pathway selection in vesicle formation was investigated. Nano-construction of O/I hybrid epoxy materials based on POSS based copolymers was investigated in Chapter4. The effect of functional group content on miscibility of POSS based statistic copolymer and epoxy was investigated. A novel method to nanostructure epoxy hybrid involving self-assembly of POSS based BCPs in epoxy was presented. High homogeneity and well size/morphology control of core-corona structure containing rigid POSS core and soluble PMMA corona in networks were obtained.

Heterogeneous line broadening and spectral diffusion of the fluorescence emission spectra of perylene diimide molecules have been investigated by means of time dependent single molecule spectroscopy. The influence of temperature and environment has been studied and reveals strong correlation to spectral diffusion processes. We followed the freezing of the molecular mobility of quasi free molecules on the surface upon temperature lowering and by embedding into a poly(methyl methacrylate) (PMMA) polymer. Thereby changes of optical transition energies as a result of both intramolecular changes of conformation and external induced dynamics by the surrounding polymer matrix could be observed. Simulations of spectral fluctuations within a two-level system (TLS) model showed good agreement with the experimental findings.

The thesis consists of four parts of which part 1 presents a brief overview of nanomaterials. Parts 2, 3 and 4 contain results of investigations of graphene, nanofilms of noble metal nanoparticles and ZnO nanostructures respectively. Investigations of graphene are described in Part 2 which consists of six chapters. In Chapter 2.1, changes in the electronic structure and properties of graphene induced by molecular charge-transfer have been discussed. Chapter 2.2 deals with the results of a study of the interaction of metal and metal oxide nanoparticles with graphene. Electrical and dielectric properties of graphene-polymer composites are presented in Chapter 2.3. Chapter 2.4 presents photo-thermal effects observed in laser-induced chemical transformations in graphene and other nanocarbons system. Chapter 2.5 describes the mechanical properties of polymer matrix composites reinforced by fewlayer graphene investigated by nano-indentation. The extraordinary synergy found in the mechanical properties of polymer matrix composites reinforced with two nanocarbons of different dimensionalities constitute the subject matter of Chapter 2.6. Investigations of noble metal nanoparticles have been described in Part 3. In Chapter 3.1, ferromagnetism exhibited by nanoparticles of noble metals is discussed in detail while Chapter 3.2 deals with surface-enhanced Raman scattering (SERS) of molecules adsorbed on nanocrystalline Au and Ag films formed at the organic–aqueous interface. Factors affecting laser-excited photoluminescence from ZnO nanostructures are examined in great detail in Part 4.

abstract: Polymer matrix composites (PMCs) are attractive structural materials due to their high stiffness to low weight ratio. However, unidirectional PMCs have low shear strength and failure can occur along kink bands that develop on compression due to plastic microbuckling that carry strains large enough to induce nonlinear matrix deformation. Reviewing the literature, a large fraction of the existing work is for uniaxial compression, and the effects of stress gradients, such as those present during bending, have not been as well explored, and these effects are bound to make difference in terms of kink band nucleation and growth. Furthermore, reports on experimental measurements of strain fields leading to and developing inside these bands in the presence of stress gradients are also scarce and need to be addressed to gain a full understanding of their behavior when UDCs are used under bending and other spatially complex stress states. In a light to bridge the aforementioned gaps, the primary focus of this work is to understand mechanisms for kink band evolution under an influence of stress-gradients induced during bending. Digital image correlation (DIC) is used to measure strains inside and around the kink bands during 3-point bending of samples with 0°/90° stacking made of Ultra-High Molecular Weight Polyethylene Fibers. Measurements indicate bands nucleate at the compression side and propagate into the sample carrying a mixture of large shear and normal strains (~33%), while also decreasing its bending stiffness. Failure was produced by a combination of plastic microbuckling and axial splitting. The microstructure of the kink bands was studied and used in a microstructurally explicit finite element model (FEM) to analyze stresses and strains at ply level in the samples during kink band evolution, using cohesive zone elements to represent the interfaces between plies. Cohesive element properties were deduced by a combination of delamination, fracture and three-point bending tests used to calibrate the FEMs. Modeling results show that the band morphology is sensitive to the shear and opening properties of the interfaces between the plies. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016