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The scarcity of freshwater is becoming a global challenge worldwide due to limited resources availability and increasing demand both for manufacturing and household use. For this reason, there is an important need to develop efficient, economic and sustainable desalination technologies able to take advantage of unconventional sources of water (seawater, brackish groundwater and wastewater) in order to produce freshwater. Sun is considered as the most promising abundant renewable (and free) energy source that can be employed in steam and vapor generation processes, which has a great importance in many applications such as: water desalination, domestic water heating, and power generation. This doctoral dissertation presents a study on the efficiency of different carbon based systems - nanofluids and hybrid natural composites - for the improvement of direct-solar evaporation systems, for the production of freshwater. The two main goals of this work consist of: (i) the synthesis and characterization of stable carbon-based nanofluids in water and of re-usable, economical and ecological hybrid composite materials, and (ii) the comparison of such carbon-based systems applied to water evaporation, understanding mechanisms, advantages and limitations. Carbon based materials (carbon black, graphene and multi-walled carbon nanotubes) were chosen because of their high sunlight absorption ability, unique thermal properties, as well as low cost and abundant availability. However, the hydrophobic character of such materials makes necessary to find efficient strategies to overcome this problem when dealing with water. In this work, the suspension stability of graphene-based nanofluids in water - a key parameter for the application of nanofluids in any field - was effectively improved by combining physical (by RF Sputtering coating) or chemical (by NaClO-NaBr solution) graphene surface modification treatments, and the use of common additives (Triton X-114, SDBS and gum arabic) showing different stabilization mechanisms. The best strategy to obtain long-time graphene suspension stability in water (both deionized water and saline solution with 3.5 wt% NaCl) turned out to be the combination of the easy chemical treatment with the electro-steric stabilization effect of gum arabic. In addition to nanofluids, a re-usable devices based on gum arabic cross-linked gelatin hydrogel were synthesized and characterized. Hydrophobic carbon-based materials were easily and uniformly embedded into the porous hydrogel matrix, thanks to the amphiphilic character of both gelatin and gum arabic. The effect of carbon-nanoparticles nature, morphology and concentration on the measured effective thermal conductivity of the composite material was studied and the thermal conductivity of the nanoparticles was evaluated applying several models based on the effective medium approach. The values obtained for the nanoparticles were far from the tabulated thermal conductivity values because of the combination of the composite features (such as nanoparticles concentration, Kapitza resistance) and the particles characteristics (such as aspect ratio, crystalline structure). The performance of carbon-based nanofluids and hybrid hydrogels on direct-solar evaporation of water was tested and compared to that of carbon-wood bilayer composite (which presents both hydrophilic character and natural channels for water transportation) under solar simulator. The effect of surface temperature, light-to-heat conversion efficiency of carbon-based materials, heat losses, water transport through a porous medium and suspension stability (in the case of nanofluids) were investigated in order to understand the advantages and limitations of such systems. All the tested systems were able to improve water evaporation rate and evaporation efficiency up to 70% and 82% under 1 sun and 2 suns respectively using a small amount of nanoparticles: the same amount of particles dispersed in nanofluid (0.01 wt%) was embedded into hydrogels or deposited onto wood. The high sunlight absorption ability of carbon-based nanoparticles appeared as a dominant parameter for the improvement of water evaporation rate. In fact, enhanced light absorption was directly related to a high photothermal conversion efficiency, which caused an improvement in the surface temperature, leading to a consequent enhancement in evaporation rate. It has been found that an adequate supply of water to the evaporation surface represents a fundamental parameter as well considering floating systems.

Cette étude constitue une contribution dans un grand projet européen dénommé : 3DICE (3D Integration of Chips using Embedding technologies). La fiabilité mécanique et thermomécanique des composants 3D a été étudiée par des essais normalisés et des simulations numériques. L’essai de chute et le cyclage thermique ont été sélectionnés pour la présente étude. Des analyses de défaillance sont menées pour compléter les approches expérimentales. Les propriétés mécaniques des éléments constituant les composants ont fait l’objet d’une compagne de caractérisation complétée par des recherches bibliographiques. Les simulations numériques, dynamiques transitoires pour l’essai de chute et thermomécanique pour l’essai de cyclage thermique, ont été réalisées pour une estimation numérique de la tenue mécanique des composants. Les modèles numériques sont utilisés pour optimiser le design des composants et prédire les durées de vie en utilisant un modèle de fatigue. / This work establishes a contribution in an important European project mentioned 3DICE (3D Integration of Chips using Embedding technologies). The mechanical and thermomechanical reliability of 3D microelectronic components are studied by employing standardized tests and numerical modeling. The board level drop test and thermal cycling reliability tests are selected for this study. Failures analysis has been used to complete the experimental study. The mechanical properties of elements constituting the microelectronic components were characterized using DMA, tensile test and nanoindentation. Bibliographical researches have been done in order to complete the materials properties data. Numerical simulations using submodeling technique were carried out using a transient dynamic model to simulate the drop test and a thermomechanical model for the thermal cycling test. Numerical results were employing in the design optimization of 3D components and the life prediction using a fatigue model.

La présente thèse doctorale vise à analyser le comportement tribologique, en corrosion et en tribocorrosion des nouveaux aciers inoxydables martensitiques et leurs mécanismes de dégradation pour applications aéronautiques. Pour ce faire, techniques électrochimiques, tribo-électrochimiques et d’analyse de surface ex-situ ont été utilisés. L'usure est affectée par la dureté du matériau et le durcissement lors du glissement de contact. Les aciers inoxydables martensitiques ont montré une augmentation de résistance à la rayure, mais une plus grande perte de matière lors des essais tribologiques à sec par rapport à l'acier inoxydable austénitique. La résistance à la corrosion des aciers inoxydables martensitiques est favorisée par leur passivité, dont la cinétique du film passif peut être décrite par un modèle de type high-field. La vitesse de dissolution passive dépend de la composition chimique de la surface du matériau, ce qui diminue la teneur en Cr dans la couche passive. Les mécanismes de dégradation en tribocorrosion des aciers inoxydables martensitiques comprennent déformation plastique, shakedown et fatigue de de type oligo-cyclique. Les conséquences de ces mécanismes impliqués dépendent des conditions électrochimiques qui prévalent. / The present Doctoral Thesis aimed to analyze the tribological, corrosion and tribocorrosion behavior of new martensitic stainless steels and their degradation mechanisms for aeronautical applications. For this, electrochemical, tribo-electrochemical and ex-situ surface analysis techniques were used. Wear damage was found to be critically affected by the hardness of the material and its hardening during sliding. Martensitic stainless steels showed higher scratch wear resistance but higher wear material loss when compared to the austenitic stainless steel. Corrosion resistance of martensitic stainless steels is driven by their passivity, whose kinetics can be described through a high field conduction model. Passive dissolution rate depends on the surface chemistry of the material, thus decreasing with the Cr content in the passive film. Degradation mechanisms involved in tribocorrosion of martensitic stainless steels included plastic deformation, shakedown and low-cycle fatigue. The consequences of those involved mechanisms depended on the prevailing electrochemical conditions. / La presente Tesis Doctoral tiene como objetivo analizar el comportamiento tribológico, frente a la corrosión y a la tribocorrosión de nuevos aceros inoxidables martensíticos y sus mecanismos de degradación en aplicaciones aeronáuticas. Para ello, se han utilizado técnicas electroquímicas, tribo-electroquímicas y de análisis de superficie ex-situ. El desgaste depende de la dureza del material y de su endurecimiento durante el deslizamiento. Los aceros inoxidables martensíticos mostraron una mayor resistencia al rallado pero una mayor pérdida de material en el ensayo tribológico de desgaste si se compara con el acero inoxidable austenítico. La resistencia a la corrosión de los aceros inoxidables martensíticos es promovida por su pasividad, cuya cinética puede ser descrita a través de un modelo de tipo high field. La velocidad de disolución pasiva depende de la química de la superficie del material, disminuyendo por lo tanto con el contenido de Cr en la película pasiva. Los mecanismos de degradación en tribocorrosión de los aceros inoxidables martensíticos incluyen deformación plástica, shakedown y fatiga de bajo ciclo. Las consecuencias de esos mecanismos dependen de las condiciones electroquímicas del sistema. / La present Tesi Doctoral té com a objectiu analitzar el comportament tribològic, front a la corrosió i a la tribocorrosió de nous acers inoxidables martensítics i els seus mecanismes de degradació en aplicacions aeronàutiques. Per tot això, s'han utilitzat tècniques electroquímiques, tribo-electroquímiques i d'anàlisi de superfície ex-situ. El desgast depen de la duresa del material i del seu enduriment durant el lliscament. Els acers inoxidables martensítics van mostrar una major resistència al ratllat però una major pèrdua de material en l'assaig tribològic de desgast si es compara amb l'acer inoxidable austenític. La resistència a la corrosió dels acers inoxidables martensítics és promoguda per la seva passivitat, i la seua la cinètica pot ser descrita a través d'un model de tipus high field. La velocitat de dissolució passiva depen de la química de la superfície del material, disminuint per tant amb el contingut de Cr en la pel·lícula passiva. Els mecanismes de degradació en tribocorrosió dels acers inoxidables martensítics inclouen deformació plàstica, shakedown i fatiga de baix cicle. Les conseqüències d'aquests mecanismes depenen de les condicions electroquímiques del sistema.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho, desenvolveu-se um sistema de detecção fotoacústico para medidas simultâneas e independentes dos sinais fotoacústicos dianteiro e traseiro, utilizando dois microfones e um único feixe de excitação. Utiliza-se a diferença de fase entre estes sinais para a determinação da difusividade térmica de materiais, com base na abordagem teórica da técnica da Diferença de Fase dos Dois Feixes (T2F). Na metodologia apresentada não há a necessidade de se alternar o feixe de excitação entre as faces da amostra. Esta característica torna mais rápido o procedimento de medida e simplifica o monitoramento automatizado de processos dinâmicos que afetam a difusividade térmica do material, como a cura de resinas poliméricas. É apresentado o procedimento utilizado para determinar a diferença entre as fases intrínsecas dos microfones e o método empregado para compensar tal diferença e, assim, obter a defasagem entre os sinais fotoacústicos dianteiro e traseiro. O sistema de detecção desenvolvido é avaliado em medidas de difusividade térmica de amostras metálicas (aço inoxidável AISI 304 e aço SAE 1020) e poliméricas (polipropileno e polietileno de baixa densidade). Os resultados obtidos concordam de forma satisfatória com dados disponíveis na literatura. Finalmente, a aplicação do sistema proposto ao monitoramento de cura de amostras de resina epóxi indicou sua potencialidade de acompanhar, em tempo real, este tipo de processo dinâmico. / In this work, a photoacoustic detection system was developed for simultaneous and independent measurements of both front and rear photoacoustic signals, using two microphones and a single beam illumination mode. The phase-lag between these signals is used in the determination of thermal diffusivity of materials, based on the theoretical approach of the Two-Beam Phase-Lag technique. In the experimental setup presented in this work there is no need to alternate the light beam between the sample surfaces. This feature provides faster measurements and simplify the automated monitoring of dynamic processes that affect the material thermal diffusivity, as crosslinking processes. The procedure to determine the difference between the intrinsic phases of the microphones is presented, as well as the method to compensate this difference and to obtain the phase-lag between front and rear photoacoustic signals. The developed detection system is tested in thermal diffusivity measurements of metallic (AISI 304 stainless steel and SAE 1020 steel) and polymeric (polypropylene and low-density polyethylene) samples. The results are in good agreement with the available literature values. Finally, the system here proposed is applied in studies of epoxy resin curing, which shows its potentiality for real-time monitoring of dynamic process.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho, desenvolveu-se um sistema de detecção fotoacústico para medidas simultâneas e independentes dos sinais fotoacústicos dianteiro e traseiro, utilizando dois microfones e um único feixe de excitação. Utiliza-se a diferença de fase entre estes sinais para a determinação da difusividade térmica de materiais, com base na abordagem teórica da técnica da Diferença de Fase dos Dois Feixes (T2F). Na metodologia apresentada não há a necessidade de se alternar o feixe de excitação entre as faces da amostra. Esta característica torna mais rápido o procedimento de medida e simplifica o monitoramento automatizado de processos dinâmicos que afetam a difusividade térmica do material, como a cura de resinas poliméricas. É apresentado o procedimento utilizado para determinar a diferença entre as fases intrínsecas dos microfones e o método empregado para compensar tal diferença e, assim, obter a defasagem entre os sinais fotoacústicos dianteiro e traseiro. O sistema de detecção desenvolvido é avaliado em medidas de difusividade térmica de amostras metálicas (aço inoxidável AISI 304 e aço SAE 1020) e poliméricas (polipropileno e polietileno de baixa densidade). Os resultados obtidos concordam de forma satisfatória com dados disponíveis na literatura. Finalmente, a aplicação do sistema proposto ao monitoramento de cura de amostras de resina epóxi indicou sua potencialidade de acompanhar, em tempo real, este tipo de processo dinâmico. / In this work, a photoacoustic detection system was developed for simultaneous and independent measurements of both front and rear photoacoustic signals, using two microphones and a single beam illumination mode. The phase-lag between these signals is used in the determination of thermal diffusivity of materials, based on the theoretical approach of the Two-Beam Phase-Lag technique. In the experimental setup presented in this work there is no need to alternate the light beam between the sample surfaces. This feature provides faster measurements and simplify the automated monitoring of dynamic processes that affect the material thermal diffusivity, as crosslinking processes. The procedure to determine the difference between the intrinsic phases of the microphones is presented, as well as the method to compensate this difference and to obtain the phase-lag between front and rear photoacoustic signals. The developed detection system is tested in thermal diffusivity measurements of metallic (AISI 304 stainless steel and SAE 1020 steel) and polymeric (polypropylene and low-density polyethylene) samples. The results are in good agreement with the available literature values. Finally, the system here proposed is applied in studies of epoxy resin curing, which shows its potentiality for real-time monitoring of dynamic process.

Submitted by Marilene Donadel (marilene.donadel@unioeste.br) on 2018-04-26T20:42:12Z No. of bitstreams: 1 Caroline_Ribeiro_2018.pdf: 4186138 bytes, checksum: e15fcfac07f7fe535fcafad4cba066dd (MD5) / Made available in DSpace on 2018-04-26T20:42:12Z (GMT). No. of bitstreams: 1 Caroline_Ribeiro_2018.pdf: 4186138 bytes, checksum: e15fcfac07f7fe535fcafad4cba066dd (MD5) Previous issue date: 2018-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work focused on the characterization of an effluent of a recycling and recovery industry of automotive batteries and on the feasibility evaluation of different materials, a biosorbent (fish scales - FS), a mineral (dolomite - DL) and a commercial material (cationic resin - CR) combined use in the removal of heavy metals. The studied materials were physico-chemically and morphologically characterized (pHpzc, MEV-EDS, FTIR and XRD) before and after their use in the removal processes in order to understand the structural modifications of the materials. In addition, the elemental composition of the liquid and solid phases after the treatment process were evaluated by TXRF analysis. The effluent presented an extremely acidic characteristic (pH = 1) and the incidence of heavy metals above the legislation discharging limits (Fe, Zn and Pb). Due to the structural characteristics and its respective functional groups, each adsorbent material presented different functional groups and different behavior in solution, which led to different removal and neutralization capacities. The CR presented the highest removal capacity of the metallic ions, mainly governed by an ion exchange process. Whilst the FS and DL presented lower removal capacities following complex simultaneous phenomena such as dissolution, complexation, precipitation and adsorption. On spite of that, the FS and DL presented a great neutralization capacity (i.e. pH elevation of the extremely acidic medium), related to the leaching of its alkaline constituents. By considering the generation of chemical sludge as a key factor in the work, aiming its mitigation and the better quality of the treated effluent, it was verified that the sequential application of these materials in hybrid process could be a promising and feasible alternative, by taking advantage of the particular characteristics of each material both in the neutralization and heavy metals’ removal. In this way, the use of DL, FS and CR in combined hybrid processes was evaluated, initially in batch system. Amongst the evaluated ones, the DL-CR hybrid process, in which the dolomite was used for the effluent neutralization up to pH = 5 followed by CR for the metallic ions removal presented better results. Therefore, the DL-CR hybrid process showed the highest percentages of metal removal (99, 73 and 100%, respectively, for Fe, Zn and Pb), as well as the lowest generation of chemical sludge by the end of the processes. In addition, the pre-neutralization (pH = 5 achieved by the DL) provided greater chemical stability of the CR. Subsequently, the DL-RC hybrid process was employed in fixed bed, evaluating the possibility of adsorption-desorption cycles aiming at the resin reuse and recovery of heavy metals. Different affinities of each metal ions by the RC for the multicomponent system (Pb> Fe> Zn) were identified, which were associated with the properties of each species as radius of hydration, valence and electron affinity. The possibility of the RC use in recycle was verified, in which similar removal capacities to the previous cycle and compatible with the levels of disposal of legislation - in terms of concentration of heavy metals as well as pH - was reached. These results demonstrate the potential of the hybrid treatment process, however, the fixed bed operating conditions such as bed height and volumetric flow still can be optimized in order to maximize mass transfer efficiency in the bed. Therefore, considering that the DL-RC hybrid process was able to overcome the treatment drawbacks of such type of effluent, due to its extremely acidic character and the complex multicomponent composition of heavy metals in solution, the process can be considered viable in technical and operational terms. In general, the cooperative use between DL and RC in hybrid process presents a remarkable potential in the neutralization and treatment of heavy metals from the battery recycling industry. / Este trabalho enfocou na caracterização de um efluente de uma indústria de reciclagem-recuperação de baterias automotivas e na avaliação de viabilidade de utilização combinada de diferentes materiais, um biossorvente (escamas de peixe - ES), um mineral (dolomita - DL) e uma material comercial (resina catiônica - RC) na remoção de metais pesados. Os materiais estudados foram caracterizados físico-química e morfologicamente (pHpzc, MEV-EDS, FTIR e DRX) antes e após sua utilização nos processos de remoção visando compreender as modificações ocorridas na sua estrutura. Além disso, a composição elementar das fases líquida e sólida após o processo de tratamento foram avaliadas por análise TXRF. O efluente apresentou caráter extremamente ácido (pH=1) e presença de metais pesados acima dos limites da legislação de descarte (Fe, Zn e Pb). Devido às características estruturais e seus respectivos grupos funcionais, cada material adsorvente apresentou comportamentos distintos em solução, o que levou a diferentes capacidades de remoção e neutralização. A RC apresentou a maior capacidade de remoção dos íons metálicos, governada majoritariamente por um processo de troca iônica. enquanto que a ES e a DL apresentaram menores capacidades de remoção seguindo fenômenos simultâneos complexos como dissolução, complexação, precipitação e adsorção. Por outro lado, a ES e a DL, apresentaram uma grande capacidade de elevação do pH dos meios extremamente ácidos, relacionado à lixiviação dos seus constituintes alcalinos. Ao considerar a geração de lama química como um fator chave no trabalho, visando sua mitigação e o a melhor qualidade do efluente tratado, verificou-se que a aplicação desses materiais de forma sequencial em processo híbrido poderia ser viável e promissora, considerando as características particulares de cada um desses materiais, tanto na neutralização quanto para remoção de metais pesados. Neste sentido, avaliou-se o uso da DL, ES e RC em processos híbridos combinados em sistema batelada, sendo o processo híbrido DL-RC, o qual empregou a dolomita na neutralização do efluente até o pH = 5 seguido pela RC para remoção dos íons metálicos a combinação que apresentou melhores resultados. O processo híbrido DL-RC apresentou as maiores porcentagens de remoção dos metais (99, 73 e 100%, respectivamente, para Fe, Zn e Pb), bem como a menor geração de lama química ao final dos processos. Além disso, a pré-neutralização (pH = 5 alcançado pela DL) proporcionou uma maior estabilidade química da RC. Posteriormente, empregou-se o processo híbrido DL-RC em leito fixo avaliando-se, ainda, a possibilidade de ciclos de adsorção-dessorção visando a reutilização da resina e recuperação dos metais pesados. Identificou-se diferentes afinidades de cada íon metálico com a RC para o sistema multicomponente (Pb > Fe > Zn), associadas às propriedades de cada espécie como raio de hidratação, valência e eletroafinidade. Verificou-se a possibilidade do uso da RC em reciclo, atingindo-se capacidades de remoção similares ao ciclo anterior e compatíveis com os níveis de descarte de legislação em termos de concentração de metais pesados bem como de pH. Tais resultados evidenciam o potencial do processo híbrido de tratamento, no entanto, as condições operacionais do leito fixo como a altura do leito e vazão volumétrica ainda podem ser otimizadas visando a maximização da eficiência de transferência de massa no leito. Desta forma, considerando-se que o processo híbrido DL-RC foi capaz de contornar a problemática do tratamento de tais efluentes dado seu caráter extremamente ácido e a complexa composição multicomponente de metais pesados em solução o processo pode ser considerado viável em termos técnico-operacionais. No geral, o uso cooperativo entre DL e RC em processo híbrido apresenta notável potencial na neutralização e tratamento de metais pesados provenientes da indústria de reciclagem de baterias.

<div>Despite the abundant current applications for ionic hydrogels, much about the stimuli-responsive behavior of these materials remains poorly understood. Due to the soft nature of these materials, the number of traditional characterization methods which can be applied to these systems is limited. Many studies have been conducted to characterize bulk property responses of these materials, and experimental studies have been produced examining the distribution of free ions around single polyelectrolyte chains. However, little experimental work has been published in which molecular-scale interactions are elucidated in confined polyelectrolyte networks. Furthermore, the way in which responsive properties, other than bulk swelling capacity, scale with ionic fraction in mixed polyelectrolyte-non-polyelectrolyte hydrogel systems has not been thoroughly investigated.</div><div>The distribution and strength of polymer-counter-ion bonds has a remarkable effect on hydrogel properties such as absorption capacity, mechanical strength, and size and chemical selectivity. In order to tailor these properties for targeted applications in ionic environments, it is imperative that we thoroughly understand the character of these polymer-ion interactions and their arrangement within the bulk hydrogel. In order to do so, however, non-traditional methods of analysis must be employed.</div><div>This dissertation focuses on a model part-ionic hydrogel system, poly(sodium acrylate-co-acrylamide), in order to assess not only the polymer-counter-ion interactions but also the impact of gel ionic fraction on these interactions and the responses which they induce in gel performance properties. A model alkali (NaCl), alkaline earth (CaCl2), and transition (CuSO4) metal salt are employed to investigate changes in polymer properties from the macroscale to the nanoscale. The aim of this dissertation is to lay the foundation for the development of fundamental structure-property relationships by which we may fully understand the ionically-induced performance properties of polyelectrolyte networks.</div>

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / A espectroscopia fotoacústica (PAS) é uma técnica não destrutiva e muito utilizada na caracterização óptica e térmica de materiais. Ela é baseada no efeito fotoacústico que consiste, basicamente, na absorção de onda eletromagnética modulada e na geração de calor no interior do material em estudo (amostra), via processo de desexcitação não-radiativa. Dentre as muitas aplicações relacionadas à caracterização de materiais, recentemente, a técnica PAS vem sendo desenvolvida para estudos de transição de fase de segunda ordem. Entretanto, poucos trabalhos são encontrados na literatura com relação à aplicação da técnica PAS ao estudo da transição vítrea. Neste contexto, o objetivo deste trabalho é o de aplicar a técnica PAS na determinação da temperatura de transição vítrea de materiais poliméricos, de uma maneira inovadora com relação à célula fotoacústica e ao sistema de aquecimento. Para isso foi projetada e construída uma célula fotoacústica que possibilita a variação de temperatura da amostra, sem afetar a curva de resposta do microfone. Foi desenvolvido um sistema de aquecimento baseado no efeito Peltier, possibilitando fazer rampas de subida de temperatura, com várias velocidades, da temperatura ambiente até 130 C, de forma linear. Todo o aparato experimental foi testado e aplicado em várias amostras poliméricas: poliamida 6.0 (Nylon); poliestireno (PS-n1921 e PS-n2380); e poli(tereftalato de etileno) (PET). Os resultados obtidos foram: para o Nylon, ; para o PS-n1921, ; para o PS-n2380, ; e para o PET, . Estes resultados estão de acordo com os respectivos valores da temperatura de transição vítrea encontrados na literatura e mostram a potencialidade da técnica PAS ao estudo da transição vítrea de materiais poliméricos. / Photoacoustic spectroscopy (PAS) is a non-destructive technique and it has been largely applied to the thermal and optical characterization of materials. PAS technique is based on the photoacoustic effect which consist, basically, absorption of a modulated electromagnetic radiation and generation of heat inside of the material studied (sample), by a nonradiative deexcitation processes. Nowadays, among many PAS applications, effort are carried out to apply PAS technique for second-order phase transitions. However, only a few works can be found in the literature about glass transition studies with PAS technique. In this context, the main goal of this work is to apply PAS technique to determine glass transition temperature of the polymeric materials, based on the new photoacoustic cell configuration and on the new heating system. In this way, a photoacoustic cell was builted up for monitoring temperature variation of the sample, where the performance of the microphone was not affected. A heating system was developed based on the Peltier effect, in such way that it is possible to scan the temperature from the environment one up to 130 C, linearly at several speeds. The experimental apparatus was tested and applied to some polymeric materials: polyamide 6.0 (Nylon); polystyrene (PS-n1921 e PS-n2380); and poli(tereftalato de etileno) (PET). The results obtained were: Nylon, ; PS-n1921, ; PS-n2380, ; and PET, . These results are in a good agreement with the respective values of glass transition temperature found in the literature and show the PAS technique potentiality for glass transition studies in polymeric materials.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / A espectroscopia fotoacústica (PAS) é uma técnica não destrutiva e muito utilizada na caracterização óptica e térmica de materiais. Ela é baseada no efeito fotoacústico que consiste, basicamente, na absorção de onda eletromagnética modulada e na geração de calor no interior do material em estudo (amostra), via processo de desexcitação não-radiativa. Dentre as muitas aplicações relacionadas à caracterização de materiais, recentemente, a técnica PAS vem sendo desenvolvida para estudos de transição de fase de segunda ordem. Entretanto, poucos trabalhos são encontrados na literatura com relação à aplicação da técnica PAS ao estudo da transição vítrea. Neste contexto, o objetivo deste trabalho é o de aplicar a técnica PAS na determinação da temperatura de transição vítrea de materiais poliméricos, de uma maneira inovadora com relação à célula fotoacústica e ao sistema de aquecimento. Para isso foi projetada e construída uma célula fotoacústica que possibilita a variação de temperatura da amostra, sem afetar a curva de resposta do microfone. Foi desenvolvido um sistema de aquecimento baseado no efeito Peltier, possibilitando fazer rampas de subida de temperatura, com várias velocidades, da temperatura ambiente até 130 C, de forma linear. Todo o aparato experimental foi testado e aplicado em várias amostras poliméricas: poliamida 6.0 (Nylon); poliestireno (PS-n1921 e PS-n2380); e poli(tereftalato de etileno) (PET). Os resultados obtidos foram: para o Nylon, ; para o PS-n1921, ; para o PS-n2380, ; e para o PET, . Estes resultados estão de acordo com os respectivos valores da temperatura de transição vítrea encontrados na literatura e mostram a potencialidade da técnica PAS ao estudo da transição vítrea de materiais poliméricos. / Photoacoustic spectroscopy (PAS) is a non-destructive technique and it has been largely applied to the thermal and optical characterization of materials. PAS technique is based on the photoacoustic effect which consist, basically, absorption of a modulated electromagnetic radiation and generation of heat inside of the material studied (sample), by a nonradiative deexcitation processes. Nowadays, among many PAS applications, effort are carried out to apply PAS technique for second-order phase transitions. However, only a few works can be found in the literature about glass transition studies with PAS technique. In this context, the main goal of this work is to apply PAS technique to determine glass transition temperature of the polymeric materials, based on the new photoacoustic cell configuration and on the new heating system. In this way, a photoacoustic cell was builted up for monitoring temperature variation of the sample, where the performance of the microphone was not affected. A heating system was developed based on the Peltier effect, in such way that it is possible to scan the temperature from the environment one up to 130 C, linearly at several speeds. The experimental apparatus was tested and applied to some polymeric materials: polyamide 6.0 (Nylon); polystyrene (PS-n1921 e PS-n2380); and poli(tereftalato de etileno) (PET). The results obtained were: Nylon, ; PS-n1921, ; PS-n2380, ; and PET, . These results are in a good agreement with the respective values of glass transition temperature found in the literature and show the PAS technique potentiality for glass transition studies in polymeric materials.