Investigou-se o efeito do \"caráter iônico\" de interfaces zwitteriônicas, formalmente neutras, representadas por micelas e vesículas obtidas de monômeros com cabeça hidrofílica dipolar, nas propriedades de acumulação e troca de espécies iônicas. Os sistemas estudados incluíram, micelas de 1-(N-hexadecil-N,N-dimetilamônio) propanossulfonato (HPS), Hexadecil fosforil colina (C16PN), 3-hexadecil glicerofostidil colina (lisoPC) e vesículas de fosfatidil colina (PC). O estudo da ligação e troca iônica nestas interfaces foi monitorado a partir de efeitos sobre reações prototrópicas de sondas como a 8-hidroxi-1,3,6-pirenotrisulfonato de sódio (piranina). Observou-se a ligação crescente da piranina na seguinte ordem lisoPC < C16PN < HPS e troca iônica com sais adicionados (função do ânion) na ordem inversa, isto é, lisoPC &gt; C16PN &gt; HPS. Estudos de reprotonação de 1 e 2 naftóis incluídos nestes agregados, via salto de pH induzido por laser, revelaram um perfil de concentração de prótons inverso àquele das cargas do dipolo, isto é, concentração nos polos negativos e exclusão nos positivos. Este resultados foram ainda reforçados por estudos de excitação de volume, via espalhamento de luz, com micelas de HPS em função de sal adicionado. A partir destes resultados propôs-se um modelo de capacitor esférico imerso em meio eletrolítico para estas interfaces, o qual se mostrou bastante versátil na análise e previsão de resultados experimentais. Em suma, estabeleceu-se no presente trabalho a visão de que interfaces dipolares são geradoras de assimetria iônica na circunvizinhança da interface, assimetria esta de polaridade invertida àquela do dipolo radialmente disposto à interface. A generalidade deste modelo pode ser extrapolado para outras interfaces e colaborar na compreensão de diversos processos que dependem da acumulação e troca iônica. / The effect of ionic domains of formally neutral zwitterionic interfaces, represented by micelles and vesicles obtained with dipolar headgroups amphiphiles, on the binding and exchange of ionic species were investigated. The systems studied included: aqueous micelles of 1-(N-hexadecyl-N,N-dimethylammonio) Propane Sulfonate (HPS), Hexadecyl Phosphoryl Choline (C16PN), and 1-hexadecylglycerophostidyl Choline (lisoPC) and vesicles of Phosphatidylcholine (PC). Binding and ion-exchange processes were assessed from the effect of these agreggates on prototropic reactions of probes such as 8-hydroxy-1,3,6-pyrenetrisulfonate pyranine). Binding of pyranine increased in the following order lisoPC < C16PN < HPS. The effectiveness of anion dependent salt displacement of the probe from the aggregates was opposite to that of affinities, i.e. lisoPC &gt; C16PN &gt; HPS. Laser pH jump studies with 1 and 2 naphtols incorporated in these aggregates revealed a proton concentration profile inverse to that of the charged dipole, that is, accumulation in the region vicinal to the negatively charged group and exclusion from the positive end of the dipole. This finding were substantiated by HPS micelle excluded volume data, obtained from light scattering studies as function of added salt. A model of a spherical capacitor immersed in an electrolyte media for these interfaces was proposed. This model accounts for satisfactorily the observed characteristics of these interfaces. The model establishes that dipolar interfaces generate ionic asymmetries in the neighborhood of the interface that opposes the radially extended monomer dipole. The generality of the model can be very helpful in the analysis and understanding of several processes occurring in/at zwitterionic interfaces.

Dióxido de carbono supercrítico (scCO2) é um solvente pouco eficiente para substâncias polares em geral. Uma maneira interessante de superar esta limitação e explorar todo o seu potencial como solvente verde, possível substituto para os solventes orgânicos voláteis comuns, é a introdução de tensoativos específicos para scCO2 no sistema. No presente trabalho, foram sintetizadas três novas séries de tensoativos oxigenados para scCO2. As moléculas possuem cabeças CO2-fóbicas mono e poli-hidroxiladas, em sua maioria à base de açúcares, e três tipos de cadeias CO2-fílicas, duas delas perfluoradas (-C7F15 e -C9F19) e uma peracetilada (derivada do ácido D-glucônico). Foram investigadas as suas solubilidades e comportamentos de fase em CO2 e em sistemas ternários (água-CO2-tensoativo), bem como a atividade na interface CO2-água. Todos eles dispersaram água em scCO2 com [água] / [tensoativo] (W) igual a 10, exibindo pressões de névoa comparáveis àquelas do sistema \"a seco\". Adicionalmente, os tensoativos reduziram a tensão interfacial CO2-água. O efeito das cabeças CO2-fóbicas e cadeias CO2-fílicas nessa redução pôde ser analisado separadamente. Os resultados dos experimentos de tensão interfacial dinâmica sugerem que tanto a difusão das moléculas da fase contínua para a subinterface, quanto a sua inserção e migração na interface contribuem para o decaimento das tensões interfaciais. / Supercritical carbon dioxide (scCO2) is a poor solvent for polar substances in general. An interesting way to overcome this limitation and fulfill its potential as a green solvent, a possible substitute for common volatile organic solvents, is the introduction of scCO2-suitable surfactants in the system. In the present work, three series of novel oxygenated surfactants for scCO2 were synthesized. The amphiphiles contain mono and poly-hydroxylated CO2-phobic heads, most of them sugar-based, as well as three types of CO2-philic tails, two of them perfluorinated (-C7F15 and -C9F19) and one peracetylated (D-gluconic acid derivative). Their solubilities and phase behaviors in CO2 and in ternary systems (water-CO2-surfactant), as well as their activities at the CO2-water interface, were investigated. All of them dispersed water in scCO2- with water-to-surfactant ratio (W) of 10, exhibiting cloud pressures comparable to those of \"dry\" systems. Also, the surfactants reduced the CO2-water interfacial tension. The effect of both the CO2-phobic heads and the CO2-philic tails could be analyzed separately. Dynamic interfacial tension results suggest that both diffusion from bulk CO2 to subinterface and insertion and migration of molecules within the interface contribute to the time-dependent decay of the interfacial tensions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo da estabilidade de emulsões de biocombustíveis destaca-se, dentre outros aspectos, pela necessidade de identificação das características destas. Esta necessidade reforça-se pela dificuldade de detecção de biodiesel e suas misturas quando estão fora de especificação, além de se aplicar aos processos de separação e purificação do biodiesel após a transesterificação. O entendimento deste problema poderá ser alcançado a partir de estudos de estabilidade associados aos modelos termodinâmicos de equilíbrio líquido-líquido (modelo NRTL) em sistemas ternários, que serão a base da modelagem proposta neste trabalho. O levantamento de dados envolve técnicas de observação direta em titulação, e ensaios de estabilidade e tensiometria, com algumas alterações das técnicas clássicas. Desta forma, o objetivo principal do trabalho é propor uma maneira de identificar e caracterizar as interfaces das emulsões formadas e estudar a estabilidade das fases envolvidas. Além disso, estuda-se a introdução de alcoóis como agentes tensoativos para viabilizar a utilização de misturas de combustíveis, mesmo na região de mais de uma fase. Para o desenvolvimento do trabalho, emulsões envolvendo os constituintes básicos serão combinadas entre si em diferentes proporções. A etapa inicial constitui-se de um mapeamento das misturas e proporções que formam as emulsões, baseadas nas curvas de equilíbrio. Em seguida, faz-se o estudo de caracterização e estabilidade destes sistemas. Com estas informações é possível mapear o sentido de incremento de tensão na interface e instabilidade da separação de fases das emulsões em relação aos diagramas ternários correspondentes. Por fim, propõe-se uma estratégia para estimar os parâmetros termodinâmicos do NRTL para as espécies presentes nos sistemas estudados e prever o comportamento dos mesmos e de sistemas similares. Este modelo matemático proposto tem como objetivo complementar a técnica experimental adotada para construção das curvas de equilíbrio, sendo bem sucedido / The study of the stability of biofuels emulsions calls attention, among other things, to the need to identify their characteristics. This need is reinforced by the difficulty of detecting biodiesel and its blends when they are out of specification, and apply the processes of biodiesel separation and purification after transesterification. The understanding of this issue could be reach from stability studies associated with thermodynamic models of liquid-liquid equilibrium (NRTL) in ternary systems, which will be the basis for modeling proposed in this paper. The research involves direct observation techniques for titration, and stability tests and tensiometry, with some changes of classical techniques. Thus, the main objective is to propose a way to identify and characterize the interfaces of emulsions formed and study the stability of the phases involved. Furthermore, it studies the introduction of alcohols as surfactants to enable the use of mixtures of fuel, even in the region of more than one phase. For development work, emulsions involving basic constituents will be combined in different proportions. The first step consists of mapping the mixtures and proportions which form emulsions, based on the equilibrium curves. Then, it is done the study of characterization and stability of these systems. With this information it is possible to map the direction of an increase in the interface tension and phase separation instability of emulsions in relation to the corresponding ternary diagrams. Finally, it proposes a strategy to estimate the thermodynamic parameters of the NRTL for the species present in the systems studied and predict the behavior of these and similar systems. This mathematical model aims to complement the experimental technique adopted for construction of the equilibrium curves, being successful

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-03-17T16:57:36Z No. of bitstreams: 1 PDF - Silvana Cartaxo da Costa.pdf: 2220034 bytes, checksum: fa6fe0b10616cb9ed70f24ac4dc15d62 (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-07-22T15:01:05Z (GMT) No. of bitstreams: 1 PDF - Silvana Cartaxo da Costa.pdf: 2220034 bytes, checksum: fa6fe0b10616cb9ed70f24ac4dc15d62 (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-07-22T15:01:16Z (GMT) No. of bitstreams: 1 PDF - Silvana Cartaxo da Costa.pdf: 2220034 bytes, checksum: fa6fe0b10616cb9ed70f24ac4dc15d62 (MD5) / Made available in DSpace on 2016-07-22T15:01:16Z (GMT). No. of bitstreams: 1 PDF - Silvana Cartaxo da Costa.pdf: 2220034 bytes, checksum: fa6fe0b10616cb9ed70f24ac4dc15d62 (MD5) Previous issue date: 2014-05-23 / The development of a colon-specific delivery system using polymeric microparticles has received great attention in the pharmaceutical field. An interesting group of polymers with potential properties in this area are the hemicellulose. Xylan is a hemicellulose that has the ability to pass through the digestive tract unchanged and its complex structure requires enzymes that are produced specifically by the human colonic microflora, which makes it an interesting raw material in the production of target drug delivery systems. The microparticulate systems can be developed by various techniques. The interfacial crosslinking polymerization is one of the major techniques to produce polysaccharide based microparticles. However, the use of highly toxic crosslinkers often makes the use of this technique limited. The sodium trimetaphosphate (TSTP), a low toxic crosslinking agent, has no adverse effects reported on human beings. The aim of this study was to develop xylan microparticles using sodium trimetaphosphate. The microparticles were characterized by optical microscopy, SEM, XRD and FT -IR. The influence of different parameters on the diameter of the microparticles was analyzed during their development. Toxicity studies against Artemia saline Leach were made to compare the microparticles produced with terephthaloyl chloride and sodium trimetaphosphate. Xylan microparticles showed to be spherical shape, well individualized and with a smooth surface. All different parameters influenced the in size of the microparticles. The FT-IR spectrum of microparticles was similar to xylan, but with the presence of the peak at 1258 cm -1 , which is typical of phosphate ester bonds, that can be attributed to the bond between TSTP and xylan during the crosslinking process. The xylan microparticles produced in this work showed no toxicity at the concentration studied. It be concluded that TSTP was able to produce xylan microparticles with well defined physicochemical characteristics and low toxicity. / O desenvolvimento de um sistema de liberação cólon-específica utilizando micropartículas poliméricas têm recebido grande atenção no campo farmacêutico. Um grupo interessante de polímeros com potenciais propriedades nessa área são as hemiceluloses. A xilana é uma hemicelulose que tem a capacidade de passar através do trato digestivo inalterada e sua complexa estrutura requer enzimas que são produzidas especificamente pela microflora colônica humana, o que a torna uma interessante matéria-prima na área produção de sistemas de liberação de fármacos. Os sistemas microparticulados podem ser desenvolvidos por várias técnicas. A reticulação polimérica interfacial é uma das principais técnicas para produção de micropartículas à base de polissacarídeos. Porém o uso de reticulantes de alta toxicidade muitas vezes torna o uso desta técnica limitada. O trimetafosfato de sódio (TSTP) é um reticulante de baixa toxicidade, sem efeitos adversos relatados em seres humanos. Esse trabalho teve como objetivo desenvolver micropartículas de xilana utilizando TSTP. As micropartículas foram caracterizadas por microscopia óptica, MEV, DRX e FT-IR. Estudos de toxicidade frente à artemia salina Leach foram feitos para comparar as micropartículas produzidas com cloridrato de tereftaloíla e trimetafosfato de sódio. As micropartículas de xilana apresentaram forma esférica, bem individualizada e com superfície bem definida. Todos os diferentes parâmetros influenciaram no tamanho das micropartículas. O espectro de FT-IR das micropartículas foi semelhante ao da xilana, porém com a presença de um pico em 1258 cm -1 , que é típico de ligações éster-fosfato, que pode ser atribuído a ligação entre TSTP e a xilana durante o processo de reticulação. As micropartículas de xilana produzidas neste trabalho não apresentaram toxicidade na concentração estudada. Podemos concluir que o TSTP foi capaz de produzir micropartículas de xilana com cracterísticas fisico-químicas bem definidas e de baixa toxicidade.

Understanding the structure and dynamics of molecularly thin films or the state of water confined to nanoscale dimensions is an active field of research and has wide applications in areas ranging from biology to geology. The issues concern fundamental aspects related to the manner in which a substrate influences the organization of water, origin of forces present when water is confined to nanoscale dimensions, and the influence on the structure and dynamics of water adjacent to a surface. The focus of this thesis lies in examining the thermodynamics and transport properties of interfacial and confined water. As a prelude to studying the structure of water confined between two mica surfaces, we first investigated the structuring of water adjacent to a single mica surface using grand canonical Monte Carlo (GCMC) simulations. The adsorption isotherm reveals three distinct stages as the relative vapor pressure in increased. The derived film thickness, isotherm shape, and heats of adsorption are in excellent agreement with recent experimental data. Our study does not support the 2D ice hypothesis and indicates that beyond the first adsorbed layer water is liquid-like. The characteristics of water confined to nanometer dimensions between two hydrophilic surfaces are investigated to assess the influence of chemical functionality of the hydrophilic surface on the structure of confined water. Our study shows that hydration of potassium ions on the mica surface has a strong influence on the water structure and solvation force response of confined water. In contrast to the disrupted hydrogen bond network observed for water confined between mica surfaces, water between silica surfaces is able to retain its hydrogen bond network displaying bulk-like structural features down to surface separations as small as 0.45 nm. An oscillatory solvation force response is observed only for water confined between silica surfaces. We evaluate and contrast the water density, dipole moment distributions, pair correlation functions and the solvation forces as a function of the surface separation. Recent experimental studies have shown that even for subnanometer confinement, the shear viscosity of water between mica surfaces is only three times larger than the free water viscosity. The dynamics of confined water between mica surfaces is evaluated using molecular dynamics simulations. Our analysis shows that the residence time for water in the contact layer is about two orders of magnitude larger than water in the central bulk-like regions between the surfaces. The K+ ions have a strong influence on the dynamics of confined water, leading to a decoupling in the translation and orientational motions. Our analysis also shows the presence of orientational jump dynamics in the contact layer near the mica surface. We also investigate the influence of confinement on the hydration characteristics of NaCl solutions both as a function of the salt concentration and the surface separation, H between graphite surfaces. A hydration limit is defined as the concentration at which a rapid drop in the hydration number is observed with increasing salt concentration. Despite a high degree of confinement, ions are able to form a quasi two-dimensional hydration shell between the two surfaces. The hydration number, reduces to about 4.15 at a pore width of H =8 A, when compared with the bulk hydration number of 6.25. In many practical situations, surfaces that are separated by an intervening fluid can be dissimilar giving rise to the so called Janus interface. In order to probe the fluid structure in such systems, we studied non-polar fluids confined between two asymmetric surfaces. By varying the degree of asymmetry between the two surfaces a wide variety of adsorption situations are examined using GCMC simulations and a mean field lattice model. The degree of asymmetry is found to influence the presence of frozen phases and can also support co-existing liquid and solid phases.

The goal of this research was to develop new experimental techniques to quantitatively study the interfacial fracture of micro-contact thin film interconnects used in microelectronic applications under monotonic and cyclic loadings. The micro-contact spring is a new technology that is based on physical vapor deposited thin film cantilevers with a purposely-imposed stress gradient through the thickness of the film. These "springs" have the promise of being the solution to address near-term wafer level probing and long-term high-density chip-to-next level microelectronic packaging challenges, as outlined by the International Technology Roadmap for Semiconductors. The success of this technology is, in part, dependent on the ability to understand the failure mechanism under monotonic and cyclic loadings. This research proposes two experimental methods to understand the interfacial fracture under such monotonic and fatigue loading conditions. To understand interfacial fracture under monotonic loading, a fixtureless superlayer-based delamination test has been developed. Using stress-engineered Cr layer and a release layer with varying width, this test can be used to measure interfacial fracture toughness under a wide range of mode mixity. This test uses common IC fabrication techniques and overcomes the shortcomings of available methods. The developed test has been used to measure the interfacial fracture toughness for Ti/Si interface. It was found that for low mode mixity Ti/Si thin film interfaces, the fracture toughness approaches the work of adhesion which is essentially the Ti-Si bond energy for a given bond density. In addition to the monotonic decohesion test, a fixtureless fatigue test is developed to investigate the interfacial crack propagation. Using a ferromagnetic material deposited on the micro-contact spring, this test employs an external magnetic field to be able to drive the interfacial crack. Fatigue crack growth can be monitored by E-beam lithography patterned metal traces that are 10 to 40nm wide and 1 to a few µm in spacing. The crack initiation and propagation can be monitored through electrical resistance measurement. In the conducted experiments, it is seen that the interfacial delamination does not occur under fatigue loading, and that the micro-contact springs are robust against interfacial fracture for probing and packaging applications.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo da estabilidade de emulsões de biocombustíveis destaca-se, dentre outros aspectos, pela necessidade de identificação das características destas. Esta necessidade reforça-se pela dificuldade de detecção de biodiesel e suas misturas quando estão fora de especificação, além de se aplicar aos processos de separação e purificação do biodiesel após a transesterificação. O entendimento deste problema poderá ser alcançado a partir de estudos de estabilidade associados aos modelos termodinâmicos de equilíbrio líquido-líquido (modelo NRTL) em sistemas ternários, que serão a base da modelagem proposta neste trabalho. O levantamento de dados envolve técnicas de observação direta em titulação, e ensaios de estabilidade e tensiometria, com algumas alterações das técnicas clássicas. Desta forma, o objetivo principal do trabalho é propor uma maneira de identificar e caracterizar as interfaces das emulsões formadas e estudar a estabilidade das fases envolvidas. Além disso, estuda-se a introdução de alcoóis como agentes tensoativos para viabilizar a utilização de misturas de combustíveis, mesmo na região de mais de uma fase. Para o desenvolvimento do trabalho, emulsões envolvendo os constituintes básicos serão combinadas entre si em diferentes proporções. A etapa inicial constitui-se de um mapeamento das misturas e proporções que formam as emulsões, baseadas nas curvas de equilíbrio. Em seguida, faz-se o estudo de caracterização e estabilidade destes sistemas. Com estas informações é possível mapear o sentido de incremento de tensão na interface e instabilidade da separação de fases das emulsões em relação aos diagramas ternários correspondentes. Por fim, propõe-se uma estratégia para estimar os parâmetros termodinâmicos do NRTL para as espécies presentes nos sistemas estudados e prever o comportamento dos mesmos e de sistemas similares. Este modelo matemático proposto tem como objetivo complementar a técnica experimental adotada para construção das curvas de equilíbrio, sendo bem sucedido / The study of the stability of biofuels emulsions calls attention, among other things, to the need to identify their characteristics. This need is reinforced by the difficulty of detecting biodiesel and its blends when they are out of specification, and apply the processes of biodiesel separation and purification after transesterification. The understanding of this issue could be reach from stability studies associated with thermodynamic models of liquid-liquid equilibrium (NRTL) in ternary systems, which will be the basis for modeling proposed in this paper. The research involves direct observation techniques for titration, and stability tests and tensiometry, with some changes of classical techniques. Thus, the main objective is to propose a way to identify and characterize the interfaces of emulsions formed and study the stability of the phases involved. Furthermore, it studies the introduction of alcohols as surfactants to enable the use of mixtures of fuel, even in the region of more than one phase. For development work, emulsions involving basic constituents will be combined in different proportions. The first step consists of mapping the mixtures and proportions which form emulsions, based on the equilibrium curves. Then, it is done the study of characterization and stability of these systems. With this information it is possible to map the direction of an increase in the interface tension and phase separation instability of emulsions in relation to the corresponding ternary diagrams. Finally, it proposes a strategy to estimate the thermodynamic parameters of the NRTL for the species present in the systems studied and predict the behavior of these and similar systems. This mathematical model aims to complement the experimental technique adopted for construction of the equilibrium curves, being successful

Made available in DSpace on 2014-12-17T15:01:33Z (GMT). No. of bitstreams: 1 JulianaLM_DISSERT.pdf: 3337263 bytes, checksum: f1607b1c73a3ec40c4bd82f3a0b43c14 (MD5) Previous issue date: 2013-08-08 / The industries of food, medicine and cosmetic apply microencapsulation for many reasons, among them, stabilize the active, control the release of encapsulated and separate incompatible components of the formulation. In this context, microencapsulation techniques have been used in the food industry to provide stable liquid and solid ingredients. Anthocyanins have high antioxidant potential, but they are photodegradable. The challenges are therefore directed to the research for techniques that could make this potential remaining active and bioavailable and could be used as a vehicle for the delivery release of bioactive and micronutrients in appropriate conditions and levels. This work has as main objective to propose a method to encapsulate the anthocyanins in the extract of mountain apple using the interfacial polymerization technique. As well as to define the ideal conditions of temperature and agitation system for this procedure. The microparticles were characterized for size, morphology, active distribution, surface charge, degradation, composition and stability. The results, like particle diameter of 5.94 &#956;m and Zeta potential of 7.03 mV, showed that the technique used to obtain these microparticles was satisfactory and has potential for application in cosmetics and food / As ind?strias de alimentos, medicamentos e cosm?ticos aplicam a microencapsula??o por diversas raz?es, dentre elas, estabilizar o ativo, controlar a libera??o do encapsulado e separar componentes incompat?veis da formula??o. Dentro deste contexto, as t?cnicas de microencapsula??o t?m sido usadas na ind?stria de alimentos para fornecer ingredientes l?quidos e s?lidos est?veis. As antocianinas possuem alto potencial antioxidante, entretanto s?o fotodegrad?veis. Os desafios s?o portanto, direcionados ? busca de t?cnicas que fa?am com que este potencial permane?a ativo e biodispon?vel para que possa ser usado como ve?culo para a libera??o de bioativos e micronutrientes, em condi??es e n?veis adequados. Este trabalho tem como objetivo principal propor uma t?cnica para encapsular as antocianinas presentes no extrato do jambo vermelho utilizando a t?cnica de polimeriza??o interfacial. Foram definidas as condi??es ideais de temperatura e agita??o do sistema para o referido processo. As micropart?culas obtidas foram caracterizadas quanto ao tamanho, morfologia, distribui??o do ativo, carga superficial, degrada??o, composi??o e estabilidade. Os resultados obtidos, tal como di?metro de part?cula de 5,94 &#956;m e potencial Zeta de +7,03 mV, mostraram que a t?cnica utilizada para obten??o destas micropart?culas foi satisfat?ria e possui potencial para aplica??o na ind?stria de cosm?ticos e alimentos

The operating efficiency and reliability of modern jet engines have undergone significant improvement largely owing to the advances of the materials science over the past 60 years. The use of both superalloys and TBCs in engine components such as turbine blades has made it possible for jet engines to operate at higher temperatures, allowing an optimal balance of fuel economy and thrust power. Despite the vast improvement in high temperature capability of superalloys, the utilization of TBCs has brought the concern of coating adhesion during their usage. TBCs are prone to spallation failure due to interfacial rumpling, which is driven primarily by thermal coefficient mismatch of the multi-layered structure. Although interfacial degradation of TBCs has been widely studied by detailed numerical and analytical models, the predicted results (i.e. stress state and rumpling amplitude) often deviate from that obtained by experiments. This is largely due to the lack of consideration of the influence of bond coat and substrate chemistry on the interfacial evolution of TBC systems. It is only in recent year that more and more study has been focused on studying the role of chemistry on the interfacial degradation of TBCs. The purpose of this PhD project is to clarify how the bond coat and substrate chemical compositions dictate the mechanisms of interfacial degradation, leading to the final spallation. A cross-sectional indentation technique was utilized to quantitatively characterize the adhesion of oxide-bond coat interface among 5 systematically prepared TBC systems. The adhesion of isothermally exposed oxide-bond coat interface was then correlated with different microstructure parameters, in an attempt to identify the key parameters controlling the TBC spallation lifetime. EBSD and EPMA analyses were conducted on the bond coat near the oxide-bond coat interface, in order to understand the relationship between the key parameters and specific alloying elements. The results clearly demonstrated that the phase transformation of bond coat near the oxide-bond coat interface plays the dominant role in the degradation of interfacial adhesion. Particularly, the co-existence of gamma prime and martensitic phases, each having very different thermomechanical response under thermal exposure, can generate a misfit stress in the TGO layer, and ultimately causes early TBC spallation. In addition, the phase transformation behavior has been closely associated with the inherent chemistry of the bond coat and substrate.

Investigou-se o efeito do \"caráter iônico\" de interfaces zwitteriônicas, formalmente neutras, representadas por micelas e vesículas obtidas de monômeros com cabeça hidrofílica dipolar, nas propriedades de acumulação e troca de espécies iônicas. Os sistemas estudados incluíram, micelas de 1-(N-hexadecil-N,N-dimetilamônio) propanossulfonato (HPS), Hexadecil fosforil colina (C16PN), 3-hexadecil glicerofostidil colina (lisoPC) e vesículas de fosfatidil colina (PC). O estudo da ligação e troca iônica nestas interfaces foi monitorado a partir de efeitos sobre reações prototrópicas de sondas como a 8-hidroxi-1,3,6-pirenotrisulfonato de sódio (piranina). Observou-se a ligação crescente da piranina na seguinte ordem lisoPC < C16PN < HPS e troca iônica com sais adicionados (função do ânion) na ordem inversa, isto é, lisoPC &gt; C16PN &gt; HPS. Estudos de reprotonação de 1 e 2 naftóis incluídos nestes agregados, via salto de pH induzido por laser, revelaram um perfil de concentração de prótons inverso àquele das cargas do dipolo, isto é, concentração nos polos negativos e exclusão nos positivos. Este resultados foram ainda reforçados por estudos de excitação de volume, via espalhamento de luz, com micelas de HPS em função de sal adicionado. A partir destes resultados propôs-se um modelo de capacitor esférico imerso em meio eletrolítico para estas interfaces, o qual se mostrou bastante versátil na análise e previsão de resultados experimentais. Em suma, estabeleceu-se no presente trabalho a visão de que interfaces dipolares são geradoras de assimetria iônica na circunvizinhança da interface, assimetria esta de polaridade invertida àquela do dipolo radialmente disposto à interface. A generalidade deste modelo pode ser extrapolado para outras interfaces e colaborar na compreensão de diversos processos que dependem da acumulação e troca iônica. / The effect of ionic domains of formally neutral zwitterionic interfaces, represented by micelles and vesicles obtained with dipolar headgroups amphiphiles, on the binding and exchange of ionic species were investigated. The systems studied included: aqueous micelles of 1-(N-hexadecyl-N,N-dimethylammonio) Propane Sulfonate (HPS), Hexadecyl Phosphoryl Choline (C16PN), and 1-hexadecylglycerophostidyl Choline (lisoPC) and vesicles of Phosphatidylcholine (PC). Binding and ion-exchange processes were assessed from the effect of these agreggates on prototropic reactions of probes such as 8-hydroxy-1,3,6-pyrenetrisulfonate pyranine). Binding of pyranine increased in the following order lisoPC < C16PN < HPS. The effectiveness of anion dependent salt displacement of the probe from the aggregates was opposite to that of affinities, i.e. lisoPC &gt; C16PN &gt; HPS. Laser pH jump studies with 1 and 2 naphtols incorporated in these aggregates revealed a proton concentration profile inverse to that of the charged dipole, that is, accumulation in the region vicinal to the negatively charged group and exclusion from the positive end of the dipole. This finding were substantiated by HPS micelle excluded volume data, obtained from light scattering studies as function of added salt. A model of a spherical capacitor immersed in an electrolyte media for these interfaces was proposed. This model accounts for satisfactorily the observed characteristics of these interfaces. The model establishes that dipolar interfaces generate ionic asymmetries in the neighborhood of the interface that opposes the radially extended monomer dipole. The generality of the model can be very helpful in the analysis and understanding of several processes occurring in/at zwitterionic interfaces.