Thesis (Ph.D.)--Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology Program in Medical Engineering and Medical Physics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Vita. / Includes bibliographical references. / by Jonathan Walker Valvano. / Ph.D.

Les enceintes de confinement sont sollicitées lors d'un accident grave par la modification thermodynamique du milieu interne qui génère une pression pouvant monter jusqu'à 5 bars, une température évaluée au maximum à 180 °C et une humidité relative pouvant aller jusqu'à la saturation. Au-delà de calculs réglementaires, la complexité de la sollicitation nécessite une bonne connaissance du comportement mécanique et thermique des matériaux et en particulier du béton dans la gamme de température et d'hygrométrie imposée afin d’être capable de mener les simulations numériques les plus réalistes possibles.Notre étude présente les évolutions des caractéristiques mécaniques et thermiques essentielles pour les simulations numériques d'un béton dans la plage de pression, température et humidité imposées lors d'un accident grave. Les essais mécanique et thermique sont réalisés sous chargement thermo-hydrique contrôlées. La température (T) est fixée à cinq valeurs cibles : 30, 90, 110, 140 et 160 °C. Les cinq degrés de saturation en eau liquide du béton (Sw) varient entre 36 % et 100 %. Les différents degrés de saturation en eau liquide des éprouvettes sont obtenus par le contrôle de l’humidité relative de l’ambiance entourant l’éprouvette pendant leur cure. L’essai DCT (Disk-shape Compact Tension) a été choisi pour déterminer l’évolution de l’énergie de fissuration, du module d'élasticité et de la résistance en traction en fonction de la température et de Sw, en raison de son caractère très compact favorable pour la mise en oeuvre des essais sous pression (essai au-delà de 100 °C). Les propriétés thermiques sont évaluées par la méthode de la Source Plane Transitoire (TPS). C’est une technique permettant de déterminer la conductivité thermique, la diffusivité thermique et d'en déduire la chaleur spécifique. L’évolution de la perméabilité relative à l’azote du béton en fonction de la température jusqu'à 90 °C et du degré de saturation en eau du béton a été évaluée également. Après avoir déterminé les propriétés thermiques et mécaniques du béton, une modélisation numérique a été réalisée afin de passer de l’échelle de laboratoire à l’échelle de la structure. Un couplage entre un modèle hydrique et un modèle d’endommagement a été réalisé. / In case of severe accident, confinement chambers are submitted to thermodynamic variations of their internal environment. Pressures can increase up to 5 bars, temperature reaches 140 °C and relative humidity attains saturation. Beyond regulatory calculations, the complexity of the solicitation needs a good knowledge of the thermo-mechanical behaviour of concrete under the imposed conditions of temperature and relative humidity. This, in turns allows to develop numerical simulations as realistic as possible. The present study investigates the evolution of the mechanical and thermal characteristics of concrete. These properties are essential to develop numerical computations under the levels of pressure, temperature and relative humidity imposed during a severe accident. Mechanical and thermal tests are carried out under controlled hydro-thermal conditions. Temperature (T) is fixed at five target values: 30, 90, 110, 140 and 160 °C. Five levels of degree of saturation (Sw) range from 36 % to 100 %. The different target values of degree of saturation are attained by controlling relative humidity in the surrounding environment of the specimens during curing. DCT (Disk-shape Compact tension) tests was chosen to determine the dependence of the fracture energy, elastic modulus and traction resistance on temperature and degree of saturation of concrete because of its compact shape that is more suitable for testing under pressure (temperature above 100°C). Thermal properties are determined by means of the Transient Plane Source (TPS) method. This technique allows to determine thermal conductivity, thermal diffusivity and hence to deduct specific heat. The dependence of the permeability to liquid nitrogen on temperature up to 90 °C and on the degree of saturation was also analysed. After determining thermal and mechanical properties of concrete, numerical simulations have been developed in order to pass from laboratory scale to the structure scale. A coupled hydro-mechanical model and a damage model are proposed.

Devido à preocupação com o meio ambiente e o volume crescente de resíduos plástico em aterros sanitários, os polímeros biodegradáveis estão sendo estudados extensivamente. Um deles é o PLA. Apesar de possuir propriedades comparáveis a polímeros commodities e polímeros de engenharia, ainda é necessário melhorar certas características do PLA, como resistência ao impacto. Para isso, a nanocelulose (NC) pode ser usada sem alterações significativas na biodegradação polimérica. Este estudo teve como objetivo obter a nanocelulose, caracteriza-la e incorpora-la ao poli(ácido láctico) (PLA), assim como, estudar as propriedades térmicas, morfológicas e mecânicas do compósito obtido. A NC foi obtida por hidrólise ácida utilizando ácido fosfórico e posteriormente foi silanizada com três silanos distintos. As nanopartículas foram caracterizadas por Birrefringência, Microscopia Eletrônica de Transmissão (MET), Termogravimetria (TG), Potencial Zeta, Espectroscopia Vibracional de Absorção no Infravermelho com Transformada de Fourier (FTIR) e Difração de Raio X (DRX). Com as imagens obtidas pelo MET foi possível medir o tamanho das partículas de NC. E então obter a razão de aspecto de 82 e o limite de percolação de 1,1% em massa, confirmando a morfologia de nanofibra. De acordo as analises TG\'s, a presença de NC silanizada aumentou o início da degradação térmica. Os compósitos, contendo 3% em massa de NC, foram obtidos por fusão em câmara de mistura e moldados por injeção. Os compósitos foram caracterizados por FTIR, Cromatografia de Permeação em Gel (GPC), TG, Calorimetria Exploratória Diferencial (DSC), Microscopia Eletrônica de Varredura (MEV-FEG), Impacto e Tração. As análises dos compósitos mostraram que a NC atuou como agente de nucleação, facilitando a cristalização do PLA, além de a NC ter atuado como reforço na matriz polimérica melhorando as propriedades mecânicas. / Due to concern for the environment and the growing volume of plastic waste in landfills, biodegradable polymers are being studied extensively. One of them is the PLA. Despite properties comparable to commodities polymers and engineering polymers, it is still necessary to improve certain characteristics of PLA, such as impact resistance. For this, the nanocelulose (CN) can be used without significant changes on the polymeric biodegradation. This study aimed to obtain nanocelulose, characterizes it and incorporates it to polylactic acid (PLA), even as, studies of thermal, morphological and mechanical properties of the composites processed. The CN was obtained by acid hydrolysis using phosphoric acid and it was, subsequently, silanized with three different silanes. The nanoparticles were characterized by Birefringence, Transmission Electron Microscopy (TEM), Thermogravimetry (TG), Zeta Potential, Spectroscopy Absorption Vibrational Infrared Fourier Transform (FTIR) and X-Ray Diffraction (XRD). By images taken by TEM was possible to measure the size of particles CN. So, obtain the aspect ratio of 82 and the percolation limit of 1.1 wt%, demonstrating morphology of nanofiber. According to TG analysis, the beginning of thermal degradation increased when CN Pure was compared with modified CN. The composite, containing 3 wt% CN, were obtained by melt in mixing chamber and then injection molded. The composites were characterized by FTIR, Gel Permeation Chromatography (GPC), TG, Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Impact and Tensile Strength. The results showed that the CN acts as a nucleating agent in PLA, facilitating the crystallization and acts as reinforcement in polymer matrix to improve the mechanical properties.

Submitted by Maria Beatriz Vieira (mbeatriz.vieira@gmail.com) on 2017-08-25T13:29:47Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tese_ane_gerber_crochemore.pdf: 1605099 bytes, checksum: 9f7ad6903f74a90dce5b9454a41d16ce (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2017-08-28T20:57:34Z (GMT) No. of bitstreams: 2 tese_ane_gerber_crochemore.pdf: 1605099 bytes, checksum: 9f7ad6903f74a90dce5b9454a41d16ce (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2017-08-28T20:58:13Z (GMT) No. of bitstreams: 2 tese_ane_gerber_crochemore.pdf: 1605099 bytes, checksum: 9f7ad6903f74a90dce5b9454a41d16ce (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-08-28T20:58:23Z (GMT). No. of bitstreams: 2 tese_ane_gerber_crochemore.pdf: 1605099 bytes, checksum: 9f7ad6903f74a90dce5b9454a41d16ce (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2014-06-27 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Os bioplásticos vêm ganhando espaço nos projetos de pesquisas e muitos já estão sendo produzidos em escala industrial e podem substituir polímeros de origem petroquímica, resultando em grande benefício ambiental. Também possuem grande potencial biotecnológico, podendo ser empregados como matéria-prima para diferentes produtos dependendo principalmente das propriedades físico-químicas e térmicas que apresentarem. Os polihidroxialcanoatos (PHAs), típicos bioplásticos totalmente biodegradáveis, são poliésteres acumulados, principalmente, por uma variedade de bactérias, como fonte de reserva de carbono e energia para a célula. O poli(3-hidroxibutirato) [P(3HB)], é o PHA mais estudado e mais comumente armazenado na forma de grânulos lipofílicos, podendo chegar a níveis de 90% em massa celular seca. O objetivo desta pesquisa foi, primeiramente, quantificar e avaliar as propriedades térmicas do polímero produzido pela Pseudomonas sp. CMM43, identificada como produtora de P(3HB), cultivada em meio nutritivo simples. Na sequência, o objetivo foi otimizar a produção de P(3HB) pela bactéria em incubador agitador orbital e biorreator bem como caracterizar os biopolímeros produzidos nas diferentes condições. Inicialmente, foi investigada a fase de multiplicação celular, alterando parâmetros de cultivo com intuito de aumentar a concentração de biomassa produzida e determinar se a produção está associada à multiplicação celular. O P(3HB) recuperado foi identificado e caracterizado. A Pseudomonas sp. CMM43 acumulou P(3HB) em 24 h, sem a necessidade de limitação de algum nutriente, sugerindo que a acumulação do polímero ocorra simultaneamente à multiplicação. O máximo conteúdo de P(3HB), 70% em relação à massa celular seca (MCS), foi obtido em meio com 1% de sacarose, pH 6,5; temperatura de 28 ºC, 250 rpm e menor aeração. O biopolímero apresentou propriedades térmicas e massa molecular reduzidas, o que permite aplicações específicas na área médica e farmacêutica. Em uma segunda fase, foram testados em agitador incubador orbital meios e concentrações de inóculo para a fase de produção do biopolímero na temperatura e aeração anteriormente selecionadas. Os P(3HB)s foram identificados e caracterizados. A máxima produção de polímero relativa à MCS foi de 83% em 48 h, no meio em que foi utilizado 10% (v/v) de inóculo e 1% de sacarose. Obtiveram-se polímeros de massa molecular reduzida e temperatura de fusão menor que a de degradação, indicando ser uma característica da bactéria e não influência do meio ou da concentração do inóculo. Por final foi avaliada a produção de P(3HB) em biorreator, aplicando o mesmo meio e condições de cultivo do estudo anterior, observando-se grande redução no acúmulo. Conclui-se que Pseudomonas sp. CMM43 possui propriedades promissoras para processos industriais de produção de P(3HB). Mesmo não tendo atingido altas concentrações celulares, a bactéria acumulou altos níveis de (P(3HB)/MCS) em 48 h, sem limitação de nutrientes e utilizando sacarose, substrato bastante econômico no Brasil. Adicionalmente, sintetiza polímeros com propriedades térmicas diferenciadas que permitem aplicabilidades específicas na área biomédica e farmacêutica. / Bioplastics have been gaining espace in research projects and many are already being produced on an industrial scale and can replace petrochemical polymers of origin, resulting in greater environmental benefit. They also have great biotechnological potential and can be used as raw material for different products depending primarily on the physical, chemical and thermal properties that show. Polyhydroxyalkanoates (PHAs), typical bioplastics completely biodegradable, are polyesters accumulated mainly by a variety of bacteria, as a source of carbon and energy reserve for the cell. The poly(3-hydroxybutyrate) [P(3HB)], is the most studied and most commonly stored as lipophilic PHA granules, reaching levels of 90% of dry cell weight. The aim of this study, was first, to quantify and evaluate the thermal properties of the produced polymer by Pseudomonas sp. CMM43, identified as producing P(3HB), cultivated in simple nutrient medium. Following aimed to optimize the production of P(3HB) by the bacteria in orbital shaker and bioreactor, and to characterize produced biopolymers in different conditions. Initially, was investigated cellular growth phase, changing cultivation parameters in order to increase the concentration of biomass produced and to determine if production is growthassociated. The P(3HB) recovered was identified and characterized. The Pseudomonas sp. CMM43 accumulated, high levels of P(3HB) at 24 h, without any nutrient limitation, suggesting that accumulation of polymer occurs simultaneously on the growth. The maximum content, 70% in the dry cell weight (DCW) was obtained in medium with sucrose, pH 6.5, temperature of 28 º C, 250 rpm and less aeration. The biopolymer presented reduced thermal properties and molecular weight, which allows specific applications in the medical and pharmaceutical area. In a second phase, was tested still in an orbital shaker incubator, media and inoculum concentration for the biopolymer production phase, in the temperature and aeration previously selected. The P(3HB) are recovered were identified and characterized. The maximum polymer yield was 83% in DCW at 48 h, in the medium which 10% (v/v) of inoculum and1% of sucrose was used. Polymers with low molecular weight and with melting temperature less than degradation were obtained, indicating that a characteristic of bacteria, and no influence on the medium or the concentration of inoculum. By the end was evaluated P(3HB) production in bioreactor, using the same medium and culture conditions of the previous study, it was observed a large reduction in the accumulation. In conclusion, Pseudomonas sp. CMM43 has promising conditions for industrial P(3HB) production processes. Despite not having reached high cell concentrations, the strain acumulated high levels (P(3HB)/DCW) for 48 h, without nutrient limitation and using sucrose, quite economical substrate in Brazil. Additionally, synthesizes polymers with different thermal properties that allow specific applicability in the biomedical and pharmaceutical field.

Submitted by OTAVIO AUGUSTO TITTON DIAS (otaviotd@gmail.com) on 2017-02-07T12:19:37Z No. of bitstreams: 1 Otávio [rev. 06.02.17] - arquivamento.pdf: 3569255 bytes, checksum: d063af8c0f50bdd6bd8ea5a53186f094 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-02-13T15:49:14Z (GMT) No. of bitstreams: 1 dias_oat_me_bot.pdf: 3569255 bytes, checksum: d063af8c0f50bdd6bd8ea5a53186f094 (MD5) / Made available in DSpace on 2017-02-13T15:49:14Z (GMT). No. of bitstreams: 1 dias_oat_me_bot.pdf: 3569255 bytes, checksum: d063af8c0f50bdd6bd8ea5a53186f094 (MD5) Previous issue date: 2016-12-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As preocupações ambientais e o esgotamento dos combustíveis fósseis resultaram em um interesse crescente em materiais ambientalmente amigáveis, à base de polímeros naturais. Esforços estão sendo feitos para introduzir a lignina em compostos plásticos, tais como polipropileno, com o objetivo de produzir materiais com boas características mecânicas e, ao mesmo tempo, ambientalmente amigáveis. A lignina é uma matéria-prima amplamente disponível na natureza, que contém alta densidade de compostos aromáticos, os quais são atualmente, em sua maioria, derivados do petróleo. No entanto, grande parte da lignina é utilizada para geração de energia e pode ser um potencial agente poluidor se não destinada de forma adequada. Desse modo, é importante encontrar uma maneira econômica de converter esse polímero natural em materiais de alto valor agregado, como compósitos com alto desempenho mecânico e térmico. Neste estudo, compósitos de polipropileno e de lignina kraft de pinus (LKI) e de bagaço de cana (LBC) foram submetidos à extrusão, e os corpos de prova foram produzidos pelo processo de injeção. Os materiais produzidos foram analisados quanto às propriedades mecânicas, térmicas (TGA, DSC, HDT), química (FTIR), reológica (índice de fluidez) e morfológica (MEV). Os objetivos desta pesquisa foram desenvolver novos compósitos de polipropileno contendo lignina e proporcionar propriedades mecânicas comparáveis aos polipropilenos comerciais, além de obter compósito com alto grau de afinidade entre a lignina e o polipropileno. Os resultados mostraram que a incorporação de lignina na matriz de polipropileno originou, de maneira geral, compósitos com propriedades adequadas para vários segmentos industriais, especialmente aqueles em que características mecânicas e térmicas são cruciais, tais como a substituição de plásticos de engenharia e polipropileno com cargas minerais. / Environmental concerns and the depletion of fossil fuels resulted in a growing interest in environmentally friendly materials based on natural polymers. Efforts are being made to introduce the lignin in plastic composites such as polypropylene, in order to produce materials with good mechanical characteristics and at the same time environmentally friendly. Lignin is a biopolymer widely available which contains high density of aromatic compounds. Nowadays, the aromatic compounds are almost exclusively derived from petroleum. However, the lignin is used mainly to generate energy and can be a pollution potential if not properly treated. Lignin, however, can improve the performance of composites. Moreover, it is important to find an economical way to convert lignin into high value-added materials. In this study, blends of polypropylene, pine kraft lignin (LKI) and sugar cane bagasse lignin (LBC) were subjected to extrusion and the specimens were produced by injection process. The materials produced were analyzed for their mechanical, thermal (TGA, DSC, HDT), chemical (FTIR), rheological (melt flow index) and morphological (SEM) properties. The objective of this research was to develop new lignin-based polypropylene composite with mechanical properties comparable to commercial polypropylene. The results showed that the incorporation of lignin in polypropylene matrix resulted in composites, in general, with properties suitable for various industrial segments, especially those in which mechanical and thermal properties are crucial, such as the replacement of engineering plastics and polypropylene mineral filled.

Submitted by Maria Aparecida (cidazen@gmail.com) on 2017-05-16T15:07:08Z No. of bitstreams: 1 Edson Carvalho Paz.pdf: 1589088 bytes, checksum: 37f9b2d6613e1ce560c6a50e8dbf458f (MD5) / Made available in DSpace on 2017-05-16T15:07:08Z (GMT). No. of bitstreams: 1 Edson Carvalho Paz.pdf: 1589088 bytes, checksum: 37f9b2d6613e1ce560c6a50e8dbf458f (MD5) Previous issue date: 2015-06-30 / CAPES, CNPQ / In this work glass formation of CaF2-CaO-B2O3-TeO2 system (CBTx), with tellurium oxide concentrations varing from 20 to 50 wt%, was studied. In order to evaluate the glass forming ability of that system, six glass matrix were prepared and characterized to understand the behavior of their physical, thermal, structural, optical and spectroscopic properties. As far we know, this is the first report in the literature about this glass system. The preparation of glasses CBTx system was carried out keeping the Ca/B2O3. The prepared glass samples were characterized by X-ray diffraction (XRD), volumetric density (ρ), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA), specific heat (cp), refractive index (n), electronic polarizability (α), theoretical optical basicity (Λth), optical absorption coefficient (Ae) and band gap optical (Eopt). The results are discussed in terms of tellurium oxide content and structural properties of the glass samples. Density, thermal stability, refractive index, electronic polarizability and theoretical optical basicity values increase with TeO2 content, while transition temperature (Tg), specific heat, optical window and the band gap optical decrease; Raman and FTIR spectroscopy indicated that the network structure of studied glass is formed by BO3, BO4, TeO3, TeO3+1 and TeO4 units. The CBTx system showed a good ability to glass formation, especially the glass matrix of most TeO2 content (CBT50), which proved to be the most suitable for future work doping with rare earth ions and tests as optical amplifier in communication fibers or other photonic devices. / Neste trabalho apresentamos o estudo da formação de vidros no sistema [10CaF2-(30-0,4x)CaO-(60-0,6x)B2O3-xTeO2], em que 20 ≤ x ≥ 50 % em massa, denominado CBTx, com o objetivo de avaliar a habilidade de formação vítrea do referido sistema visando obter matrizes vítreas estáveis. Até onde sabemos, este é o primeiro relato na literatura de pesquisas sobre esse sistema. O preparo dos vidros no sistema CBTx foi realizado mantendo constante a razão Ca/B2O3. Neste trabalho sintetizamos seis amostras vítreas, as quais foram submetidas ao processo de caracterização por meio das seguintes análises: difração de raios-X (DRX), densidade de massa volumétrica (ρ), espectroscopia Raman, espectroscopia no infravermelho com transformada de Fourier (FTIR), análise térmica diferencial (DTA), calor específico (cp), índice de refração (n), polarizabilidade eletrônica (α), basicidade óptica teórica (Λth), coeficiente de absorção óptica (Ae) e band gap óptico (Eopt). Os resultados foram discutidos em função do conteúdo de óxido de telúrio e de suas alterações nas propriedades estruturais, térmicas, ópticas e espectroscópicas das amostras vítreas. Com o aumento da concentração de TeO2 nas amostras, houve aumento dos valores da densidade, da estabilidade térmica, do índice de refração, da polarizabilidade eletrônica e da basicidade óptica teórica; redução da temperatura de transição vítrea (Tg), do calor específico e da janela óptica e deslocamento do band gap óptico para menor energia; as espectroscopias Raman e FTIR indicaram que a estrutura da rede dos vidros sob investigação é formada por unidades BO3, BO4, TeO3, TeO3+1 e TeO4. O sistema CBTx apresentou uma boa habilidade de formação vítrea, com destaque para a matriz vítrea de maior teor estudado de TeO2 (CBT50), que se mostrou a mais indicada para trabalhos futuros de dopagem com íons terras raras e testes como amplificador óptico em fibras de comunicação ou outros dispositivos fotônicos.

As nanocomposites provide considerable improvements in material properties, scientists and engineers are focussing on biodegradable nanocomposites having superior material properties as well as degradability. This thesis has investigated the properties of biodegradable nanocomposites of the aliphatic thermoplastic polyester, poly (lactide acid) (PLA) and the synthetic biodegradable polyester, poly (butylene succinate) (PBS). To enhance the properties of this blend, nanometer-sized clay particles, have been added to produce tertiary nanocomposite. High aspect ratio and surface area of clay provide significant improvement in structural, mechanical, thermal and barrier properties in comparison to the base polymer. In this study, a series of PLA/PBS/layered silicate nanocomposites were produced by using a simple twin-screw extruder. PLA/PBS/Cloisite 30BX nanocomposites were prepared containing 1, 3, 5, 7 and 10 wt% of C30BX clay, while PLA and PBS polymers compositions were fixed at a ratio of 80 to 20. This study also included the validation of a gas barrier model for these biodegradable nanocomposites. WAXD indicated an exfoliated structure for nanocomposites having 1 and 3 wt% of clay, while predominantly development of intercalated structures was noticed for nanocomposites higher than 5 wt% of clay. However, TEM images confirmed a mixed morphology of intercalated and exfoliated structure for nanocomposite having 1 wt% of clay, while some clusters or agglomerated tactoids were detected for nanocomposites having more than 3 wt% of clay contents. The percolation threshold region for these nanocomposites lied between 3-5 wt% of clay loadings. Liquid-like behaviour of PLA/PBS blends gradually changed to solid-like behaviour with the increase in concentration of clay. Shear viscosity for the nanocomposites decreased as shear rate increased, exhibiting shear thinning non-Newtonian behaviour. Tensile strength and Young's modulus initially increased for nanocomposites of up to 3 wt% of clay but then decreased with the introduction of more clay. At high clay content (more than 3 wt%), clay particles tend to aggregate which causes microcracks at the interface of clay-polymer by lowering the polymer-clay interaction. Percentage elongation at break did not show any improvement with the addition of clay. PLA/PBS blends were considered as immiscible with each other as two separate glass transition and melting temperatures were observed in modulated differential scanning calorimetry (MDSC) thermograms. MDSC showed that crystallinity of the nanocomposites was not much affected by the addition of clay and hence some compatibilizer is required. Thermogravimetric analysis showed that the nanocomposite containing 3 wt% of clay demonstrated highest thermal stability compared to other nanocomposites. Decrease in thermal stability was noticed above 3 wt% clay; however the initial degradation temperature of nanocomposites with 5, 7 and 10 wt% of clay was higher than that of PLA/PBS blend alone. Gas barrier property measurements were undertaken to investigate the transmission of oxygen gas and water vapours. Oxygen barrier properties showed significant improvement with these nanocomposites, while that for water vapour modest improvement was observed. By comparing the relative permeabilities obtained from the experiments and the model, it was concluded that PLA/PBS/clay nanocomposites validated the Bharadwaj model for up to 3 wt% of clay concentration.

Silver containing chalcogenide glasses have been extensively studied during the last few decades; the main interest in these materials being their electrical conductivity which changes by several orders of magnitude upon silver doping. Glassy chalcogenides doped with silver have applications in optical elements, gratings, micro-lenses, waveguides, bio & chemical sensors, solid electrolytes, batteries, etc. Chalcohalide glasses have become important in the recent times, from both scientific & technological points of view, due to the interesting properties exhibited by these glasses such as the transparency in the infrared region, the stability against devitrification, solubility of rare earth elements, etc. In this thesis work, the thermal properties and electrical switching behavior of certain silver and iodine doped chalcogenide glasses have been investigated The thesis contains five chapters: Chapter 1: This chapter is an introduction to the fundamental aspects of amorphous semiconductors with a particular reference to chalcogenide glasses. The advantages and applications of chalcogenide glasses are also described. Chapter 2: The methods of preparation and characterization of the glasses investigated are described in this chapter. Also, the details of the experiments undertaken, namely temperature modulated Alternating Differential Scanning Calorimetry (ADSC), electrical switching analysis, Photo-thermal Deflection Spectroscopy (PDS), etc, are outlined. Chapter 3: In this chapter, the thermal behavior and electrical switching of silver doped Ge-Se and As-Se chalcogenide glasses are described. Bulk, melt-quenched Se-rich Ge0.15Se0.85-xAgx glasses have been found to be microscopically phase separated and composed of Ag2Se clusters and GeSe2-Se network. When the silver concentration exceeds 10 atom %, the Ag2Se clusters embedded in the GeSe2-Se network percolate. The signature of this percolation threshold is clearly observed as the sudden appearance of two exothermic crystallization peaks in ADSC runs. Density, molar volume and micro hardness studies also strongly support the view of a percolation transition. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be connected with the silver phase percolation. It has been found that Ge0.15Se0.85-xAgx glasses of lower silver concentration (x = 0.07 and 0.08) do not exhibit electrical switching at voltages up to 1100 V. A negative resistance behavior and threshold type electrical switching is seen in Ge0.15Se0.85-xAgx samples with x 0.09. Also, fluctuations are observed in the I-V characteristics of these samples, which have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the Ge-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 0.10, is related to silver phase percolation in these glasses. Bulk As20Se80-xAgx glasses (0 x 15) have been found to exhibit two endothermic glass transitions and two exothermic crystallization reactions on heating. Based on which it is suggested that As20Se80-xAgx glasses are also microscopically phase separated, containing Ag2Se phases embedded in an As-Se backbone. The occurrence of microscopic phase separation in As20Se80-xAgx glasses is also confirmed by SEM studies. With increasing silver concentration, the Ag2Se phase percolates in the As-Se matrix, with a well-defined percolation threshold at x = 8. This silver phase percolation is exemplified by sudden jumps in the composition dependence of the second crystallization peak and non-reversible heat-flow, Hnr obtained at the second glass transition reaction of As20Se80-xAgx glasses. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be associated with the observed silver phase percolation. Like Ge0.15Se0.85-xAgx glasses, As20Se80-xAgx glasses also exhibit threshold type electrical switching with fluctuations in the I-V characteristics; these fluctuations have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the As-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 8, is found to be related to silver phase percolation in these glasses, which has been proposed on the basis of ADSC experiments. Chapter 4: The chapter 4 deals with thermal studies, electrical switching investigations and Photo-thermal Deflection Spectroscopic (PDS) measurements on certain Ge-Te-I and As-Te-I chalcohalide glasses. It has been found that the compositional variation of the glass transition temperature of Ge22Te78-xIx glasses, obtained by Alternating Differential Scanning Calorimetry (ADSC), exhibits a broad hump around 5 atom % of iodine. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy (Hnr) of Ge22Te78-xIx glasses at x = 5, which is suggestive of a thermally reversing window at this composition. Electrical switching studies on Ge22Te78-xIx glasses indicate that these glasses exhibit memory type electrical switching. At lower iodine concentrations, a decrease is seen in switching voltages with an increase in iodine content (in comparison with the base Ge22Te78 glass), which is due to the decrease in network connectivity. The increase seen in switching voltages of Ge22Te78-xIx glasses at higher iodine contents, suggests that the influence of the metallicity is stronger at higher iodine proportions. It is also interesting to note that the composition dependence of the threshold voltages shows a slope change at x = 5, the inverse rigidity percolation threshold of the Ge22Te78-xIx system. . Further, it is found that the thermal diffusivities ( D) of Ge22Te78-xIx glasses decrease with the increase in iodine content, which has been understood on the basis of fragmentation of the Ge-Te network with the addition of iodine. Also, a cusp is seen in the composition dependence of thermal diffusivity at the composition x = 5 (average coordination number, r = 2.39), which has been identified to be the inverse rigidity percolation threshold of the system at which the network connectivity is lost. ADSC studies on As45Te55-xIx chalcohalide glasses (3 x 10) reveal that there is not much variation in the glass transition temperature of As45Te55-xIx glasses, even though there is a wide variation in r . Based on this observation we suggest that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than the average coordination number. Further, the non-reversing enthalpy Hnr of As45Te55-xIx glasses is found to exhibit a sharp minimum at the composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 x 7. These results indicate a narrow thermally reversing window in As45Te55-xIx glasses around the composition x = 6. As45Te55-xIx glasses have been found to exhibit a memory to threshold type change in switching behavior with iodine content (x 6), which has been understood on the basis of the sharp increase in thermal diffusivity above x = 6. It is also observed that the switching voltages do not change appreciably with composition/average coordination number. Though no pronounced signature of a stiffness transition is seen in the variation with composition of VT, fluctuations are seen in the switching voltages around x = 6, the composition corresponding to the sharp thermally revering window. PDS studies indicate that the thermal diffusivities () of As45Te55-xIx chalcohalide exhibit a sharp minimum at the composition x = 6. This result reasserts the presence of a sharp thermally reversing window in As45Te55-xIx glasses around the composition x = 6. Chapter 5: The significant results obtained in the present thesis work have been summarized in this chapter. Further, the scope for future work is also presented.

As the integration scale of transistors/devices in a chip/system keeps increasing, effective cooling has become more and more important in microelectronics. To address the thermal dissipation issue, one important solution is to develop thermal interface materials with higher performance. Carbon nanotubes, given their high intrinsic thermal and mechanical properties, and their high thermal and chemical stabilities, have received extensive attention from both academia and industry as a candidate for high-performance thermal interface materials. The thesis is devoted to addressing some challenges related to the potential application of carbon nanotubes as thermal interface materials in microelectronics. These challenges include: 1) controlled synthesis of vertically aligned carbon nanotubes on various bulk substrates via chemical vapor deposition and the fundamental understanding involved; 2) development of a scalable annealing process to improve the intrinsic properties of synthesized carbon nanotubes; 3) development of a state-of-art assembling process to effectively implement high-quality vertically aligned carbon nanotubes into a flip-chip assembly; 4) a reliable thermal measurement of intrinsic thermal transport property of vertically aligned carbon nanotube films; 5) improvement of interfacial thermal transport between carbon nanotubes and other materials. The major achievements are summarized. 1. Based on the fundamental understanding of catalytic chemical vapor deposition processes and the growth mechanism of carbon nanotube, fast synthesis of high-quality vertically aligned carbon nanotubes on various bulk substrates (e.g., copper, quartz, silicon, aluminum oxide, etc.) has been successfully achieved. The synthesis of vertically aligned carbon nanotubes on the bulk copper substrate by the thermal chemical vapor deposition process has set a world record. In order to functionalize the synthesized carbon nanotubes while maintaining their good vertical alignment, an in situ functionalization process has for the first time been demonstrated. The in situ functionalization renders the vertically aligned carbon nanotubes a proper chemical reactivity for forming chemical bonding with other substrate materials such as gold and silicon. 2. An ultrafast microwave annealing process has been developed to reduce the defect density in vertically aligned carbon nanotubes. Raman and thermogravimetric analyses have shown a distinct defect reduction in the CNTs annealed in microwave for 3 min. Fibers spun from the as-annealed CNTs, in comparison with those from the pristine CNTs, show increases of ~35% and ~65%, respectively, in tensile strength (~0.8 GPa) and modulus (~90 GPa) during tensile testing; an ~20% improvement in electrical conductivity (~80000 S m⁻¹) was also reported. The mechanism of the microwave response of CNTs was discussed. Such an microwave annealing process has been extended to the preparation of reduced graphene oxide. 3. Based on the fundamental understanding of interfacial thermal transport and surface chemistry of metals and carbon nanotubes, two major transfer/assembling processes have been developed: molecular bonding and metal bonding. Effective improvement of the interfacial thermal transport has been achieved by the interfacial bonding. 4. The thermal diffusivity of vertically aligned carbon nanotube (VACNT, multi-walled) films was measured by a laser flash technique, and shown to be ~30 mm² s⁻¹ along the tube-alignment direction. The calculated thermal conductivities of the VACNT film and the individual CNTs are ~27 and ~540 W m⁻¹ K⁻¹, respectively. The technique was verified to be reliable although a proper sampling procedure is critical. A systematic parametric study of the effects of defects, buckling, tip-to-tip contacts, packing density, and tube-tube interaction on the thermal diffusivity was carried out. Defects and buckling decreased the thermal diffusivity dramatically. An increased packing density was beneficial in increasing the collective thermal conductivity of the VACNT film; however, the increased tube-tube interaction in dense VACNT films decreased the thermal conductivity of the individual CNTs. The tip-to-tip contact resistance was shown to be ~1×10⁻⁷ m² K W⁻¹. The study will shed light on the potential application of VACNTs as thermal interface materials in microelectronic packaging. 5. A combined process of in situ functionalization and microwave curing has been developed to effective enhance the interface between carbon nanotubes and the epoxy matrix. Effective medium theory has been used to analyze the interfacial thermal resistance between carbon nanotubes and polymer matrix, and that between graphite nanoplatlets and polymer matrix.

A study was done to determine the temperature and load interaction effects on the fatigue crack growth rate of polycrystalline superalloy IN100. Temperature interaction testing was performed by cycling between 316°C and 649°C in blocks of 1, 10 and 100 cycles. Load interaction testing in the form of single overloads was performed at 316°C and 649°C. After compiling a database of constant temperature, constant amplitude FCGR data for IN100, fatigue crack growth predictions assuming no load or temperature interactions were made. Experimental fatigue crack propagation data was then compared and contrasted with these predictions. Through the aid of scanning electron microscopy the fracture mechanisms observed during interaction testing were compared with the mechanisms present during constant temperature, constant amplitude testing. One block alternating temperature interaction testing grew significantly faster than the non-interaction prediction, while ten block alternating temperature interaction testing also grew faster but not to the same extent. One hundred block alternating testing grew slower than non-interaction predictions. It was found that as the number of alternating temperature cycles increased, changes in the gamma prime morphology (and hence deformation mode) caused changes in the environmental interactions thus demonstrating the sensitivity of the environmental interaction on the details of the deformation mode. SEM fractography was used to show that at low alternating cycles, 316°C crack growth was accelerated due to crack tip embrittlement caused by 649°C cycling. At higher alternating cycles the 316°C cycling quickly grew through the embrittled crack tip but then grew slower than expected due to the possible formation of Kear-Wilsdorf locks at 649°C. Overload interaction testing led to full crack retardation at 2.0x overloads for both 316°C and 649°C testing. 1.6x overloading at both temperatures led to retarded crack growth whereas 1.3x overloads at 649°C created accelerated crack growth and at 316°C the crack growth was retarded.