Les propriétés viscoélastiques des fluides déterminent leur écoulement. L’étude de ces propriétés a de nombreuses applications industrielles et académiques qui concernent la matière dite « molle » (polymères, colloïdes, tensioactifs, protéines, ...). L’approche proposée permet d'étudier ces propriétés sur une gamme de fréquence allant de 1 à 100 kHz. La méthode utilise la mesure de la vibration d’une microstructure actionnée électromagnétiquement et immergée dans le fluide à caractériser. La réponse en fréquence du système mécanique, mesurée optiquement ou électriquement, est caractéristique du milieu dans lequel la structure est immergée. Une méthode analytique dédiée aux micropoutres, pour l’extraction des propriétés rhéologiques du milieu, a été améliorée tout au long de la thèse.La méthode analytique développée, pour être appliquée, nécessite la précision d’un système optique complexe pour mesurer sans artefact les propriétés mécaniques de l’interaction micropoutre-liquide. Ainsi les liquides opaques ne peuvent être caractérisés avec cette approche. De plus la mesure peut difficilement être intégrée dans un dispositif portable tout-électronique. Afin de pallier ces difficultés et de proposer une mesure de la viscoélasticité en milieu opaque, la stratégie de mesure du capteur jusqu’au traitement des signaux ont été réévalués : (1) des microstructures en « U » ont été fabriquées, (2) une méthode de mesure intégrée a été mise en place et (3) une méthode de traitement à fréquence unique a été utilisée. Finalement, un liquide opaque viscoélastique, le yaourt, a pu être caractérisé in-situ tout au long de la fermentation lactique permettant de démontrer la validité et l’applicabilité de la méthode mise en œuvre pour le suivi en temps réel de la viscoélasticité. / The study of viscoelastic properties has many industrial and academic applications related to "soft matter" like polymers, colloids, surfactants or proteins. The present approach measures these properties in a frequency range from 1 to 100 kHz. The method uses the measurement of the vibration of a microstructure actuated electromagnetically and immersed in the fluid that has to be characterized. The frequency response of the mechanical system, which is measured optically or electrically, is characteristic of the environment in which the structure is immersed in. An analytical method dedicated to microcantilevers for the extraction of the rheological properties has been improved during this PhD thesis.The analytical method developed requires the accuracy of a complex optical system for measuring without artifact the mechanical properties of microcantilever-liquid interaction. Thus opaque liquids cannot be characterized with this sytem. In addition, the measurement cannot easily be integrated. To overcome these difficulties and provide the measurement of viscoelasticity into opaque medium, some strategy was reassessed: (1) “U” shaped microstructures were fabricated; (2) an integrated measurement method was developed and (3) a single frequency method was used to calculate the viscoelasticity.Finally, a viscoelastic and opaque liquid, such as yogurt, has been characterized in situ during the lactic fermentation to demonstrate the validity and the applicability of the method for the real-time monitoring of viscoelasticity.

Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-10-10T13:21:42Z No. of bitstreams: 1 TeseAM.pdf: 7680112 bytes, checksum: c8ecf6ee83f4312fa3be9569904c7b2f (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-20T19:45:26Z (GMT) No. of bitstreams: 1 TeseAM.pdf: 7680112 bytes, checksum: c8ecf6ee83f4312fa3be9569904c7b2f (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-20T19:45:32Z (GMT) No. of bitstreams: 1 TeseAM.pdf: 7680112 bytes, checksum: c8ecf6ee83f4312fa3be9569904c7b2f (MD5) / Made available in DSpace on 2016-10-20T19:45:37Z (GMT). No. of bitstreams: 1 TeseAM.pdf: 7680112 bytes, checksum: c8ecf6ee83f4312fa3be9569904c7b2f (MD5) Previous issue date: 2016-07-11 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / This study presents the development of a biosensor using a microcantilever stem and its detecting response through dynamic mode of atomic force microscopy (AFM). Responses of different methods for immobilization of alcohol dehydrogenase enzyme were investigated in order to accomplish a selective detection of ethanol, methanol and isopropanol, using as arrays: self-assembly monolayer (SAM) and others arrangements formed on Si and Si3N4 microcantilevers surface. In addition, we aimed to evaluate the influence of the biological element immobilization process in the analytical performance of the biosensor. The process to development of a biosensor began with the activation of its surface by means of thiols and silanes with different carbon length chains, however with the same amine terminal groups (NH2). The microcantilevers activation is only possible with the oxidation of its surface and to check this process, the "High-resolution Xray Photoelectron Spectroscopy (XPS)" technique was used. Activation of the surface was obtained using different methods for coating of microcantilevers made only with Si (100) and Si3N4. Subsequently to the oxidation process, the binding of the biomolecule to the surface activated was performed using the bifunctional agent glutaraldehyde. Microcantilevers with both sides coated by biomolecules were investigated and a tension effect of surface was observed at a 0,3 mL/L of the target analyte. By analyzing the performance of the biosensor for the determination of the target analyte, it was realized that APTES activation methodology for biosensors steam and self-assembled monolayers were the most suitable techniques for immobilizing the recognition biomolecule. With this preparation, the biosensor it showed less susceptible to humidity and the temperature variations, presenting a high quality factor, a faster response time, selectivity, sensitivity and durability. / Este trabalho apresenta o desenvolvimento de um biossensor, utilizando a haste de microcantilever e a detecção de sua resposta por intermédio do modo dinâmico da microscopia de força atômica (AFM). Foram investigadas as respostas de diferentes métodos para imobilização da enzima Álcool Desidrogenase, a fim de realizar a detecção seletiva de etanol, metanol e isopropanol, empregando como matrizes monocamadas auto-organizadas (SAM – Self Assembed Monolayer) e outros arranjos formados sobre a superfície de microcantilevers de Si e Si3N4. Além disso, objetivou-se a avaliação da influência do processo de imobilização do elemento biológico no desempenho analítico do biossensor. O processo de desenvolvimento do biossensor iniciou-se com a ativação de sua superfície por meio de deposição de tióis e silanos com diferentes comprimentos de cadeias carbônicas, mas com os mesmos grupos terminais amina (NH2). A ativação de microcantilevers somente é possível com a oxidação de sua superfície e para verificação desse processo foi empregada a técnica “High-resolution Xray Photoelectron Spectroscopy (XPS)”. A ativação da superfície foi obtida utilizando metodologias diferentes para o recobrimento dos microcantilevers construídos somente com Si (100) e Si3N4. Posteriormente ao processo de oxidação, segue-se a ligação da biomolécula à superfície ativada pela utilização do agente bifuncional Glutaraldeído. Foram investigados microcantilevers em que ambos os lados foram revestidos com as biomoléculas e, foi constatado o efeito da tensão superficial a partir de 0,3 mL/L do analito alvo. Ao analisar o desempenho do biossensor para a determinação do analito alvo, verificou-se que nos biossensores a metodologia de ativação por vapor de (3-Aminopropyl)triethoxysilane (APTES) e com montagem em monocamadas auto-organizada foi a mais adequada para a imobilização da biomolécula de reconhecimento, com esta preparação o biossensor foi menos susceptível a umidade relativa e variações de temperatura apresentando elevado fator de qualidade, menor período de tempo de resposta, seletividade, durabilidade e sensibilidade.

Ces travaux de thèse sont le fruit d’un constat : le développement des matériaux organiques dans les MEMS ne cesse de croître. Cela est dû à leurs procédés de fabrication à moindre coût et à leurs propriétés qui diffèrent de celles des matériaux inorganiques. D’un point de vue biologique,les propriétés physiques et chimiques des matériaux organiques sont également plus proches des propriétés de l’environnement extra-cellulaire. Les MEMS sont des systèmes très polyvalents permettant de mesurer de nombreuses grandeurs physiques. Leur utilisation dans le domaine biologique n’est donc pas étonnante et il est intéressant de combiner les MEMS avec des matériaux organique pour l’étude de cellules. L’objectif de ces travaux est de fabriquer et d’utiliser des résonateurs MEMS organiques piézoélectriques dans le but d’étudier la biomécanique et l’adhésion de cellules. En effet,la biomécanique des cellules est un domaine d’étude qui renseigne sur de nombreux processus opérés par les cellules, comme l’adhésion cellulaire, ainsi que sur leur bien être. Dans un premier temps, le procédé de fabrication des résonateurs a été établi et optimisé afin d’obtenir une efficacité d’actionnement piézoélectrique maximale. Dans un deuxième temps, un système d’actionnement et de mesure électrique a été réalisé, comportant une carte électronique ainsi qu’une enceinte étanche. L’influence de la température, de la densité et de la viscosité du milieu sur la résonance des MEMS a également été étudiée. Finalement, les résonateurs créés ont été utilisés dans le suivi en temps réel de l’adhésion de cellules souches mésenchymateuses. D’autres applications ont été réalisées avec les résonateurs piézoélectriques comme l’étude de la position d’une masse sur les résonateurs, la détermination de la rigidité d’un matériau ainsi que de la viscosité d’un liquide. / This PhD thesis is the result of an assessment : the use of organic materials in MEMSis in a constant increase. Organic materials are attractive because of their low-cost fabrication processand their properties that are different from the inorganic ones. From a biological point of view, theirphysical and chemical properties are closer to the properties of extracellular environment. MEMS arevery versatile systems that are able to measure a lot of physical quantities. Therefore, it is not surprisingto use them in biology, and combining MEMS with organic materials is really promising tostudy biological cells behavior. The objective of this work is to fabricate and use piezoelectric organicMEMS resonators to study cell biomechanics and adhesion. In fact, the study of cell biomechanicsgives information on a lot of cellular processes, like the cellular adhesion, as well as on their well-being.Firstly, the resonators fabrication process has been developed and optimized in order to maximize thepiezoelectric actuation. Secondly, an electronic actuation and measurement system has been realized,including an electronic card and a watertight enclosure. The influence of the temperature, mass densityand viscosity of the environment on the dynamic response of the resonators has also been evaluated.Finally, real time measurements of the adhesion of mesenchymal stem cells have been carried out usingthe resonators. The resonators have also been used to study the influence of the position of a mass onthe resonators, to determine the rigidity of a deposited material as well as the viscosity of liquid media.

La lutte contre le terrorisme et le trafic de narcotiques sont devenus des enjeux sociétaux majeurs. Par exemple, l’identification rapide des colis piégés est aujourd’hui indispensable dans les lieux publics, motivant le développement de systèmes de détection de types nez électroniques. Ce travail de recherche, porte sur l’étude des transducteurs MEMS de type microleviers et SAW (surface acoustic wave), choisis parmi les différentes familles de biocapteurs existants pour leurs nombreux avantages tels que leur grande sensibilité à détecter tous types de molécules. Cette thèse est axée sur l’étude de ces deux types de MEMS en diamant combinés à des biorécepteurs olfactifs spécifiquement impliqués dans la perception et la reconnaissance des odeurs. Les propriétés physiques et chimiques exceptionnelles du diamant déposé sur leur surface ont permis le développement de détecteurs à la fois miniaturisés, robustes et sensibles. La chimie unique du diamant a permis en particulier d’immobiliser sur la surface de ces transducteurs différents types de biorécepteurs de type OBP (Odorant Binding Protein), MUP (Major Urinary Protein) et OR (récepteurs olfactifs) comme couche sensible. L’immobilisation de ces LBP sur les MEMS en diamant a été caractérisée par diverses techniques telles que la spectroscopie électrochimique d’impédance (EIS), la spectroscopie de fluorescence ou encore la spectroscopie XPS. Les performances des capteurs ont été suivies par vibrométrie laser dans le cas des microleviers et à l’aide d’un système d’acquisition commercial dans le cas des SAW, en mesurant les déplacements de fréquence de résonance lors d’exposition aux composés cibles. Une comparaison entre les différents types de LBP provenant de différentes espèces (mammifères, insectes) a été effectuée en termes de sensibilité lors d’exposition à des drogues et des composés explosifs. Les limites de détections (LOD) obtenues dans nos conditions de mesures se situent dans la gamme d’1µg jusqu’à 35 ng par exemple pour l’héroïne, en fonction des espèces cibles testées. La LOD du TNT est d’environ 100 ng. / Over the last decade, the need for resources devoted to counter terrorism as well as narcotic trafficking has grown. Thus the effective fight against those scourges requires the development of advanced physical and chemical detection systems and sensor systems such as electronic noses able to detect drugs and explosives compounds. In this context, ligand binding proteins (LBP) combined to diamond MEMS such as resonant microcantilevers and surface acoustic wave (SAW) sensors are foreseen as highly promising transducers for the design of label free biosensors in particular for the detection of small organic molecules. LBP are small proteins involved in the perception and recognition of odorant molecules. In this study, OBP (Odorant Binding Protein), MUP (Major Urinary Protein) and OR (olfactory receptor) were used to bind selected analytes. The carbon nature of diamond offers wide opportunities for stable grafting of such bioreceptors. The performances of these transducers present a real improvement in terms of speed, miniaturization and sensitivity. Immobilization of LBP on diamond transducers was investigated using fluorescence methods, electrical impedance spectroscopy (EIS) and X-Ray photoelectron spectroscopy (XPS). The sensing performances of the resulting biosensors were assessed by monitoring the frequency shift in real time upon exposure to the target molecules. We compared different kind of LBP, coming from vertebrates, insects, mutant or wild type in terms of sensitivity, selectivity and for their capability to bind odors, explosive and drug compounds. Within our experimental conditions, the detection of a wide variety of drugs and explosives was possible in the concentration range typically from 1 µg to e.g. 35 ng in the case of heroin, depending on the test substances. The limit of detection of TNT compound is about 100 ng.

A miniaturização de elementos mecânicos como pontes e vigas por meio de processos de fabricação antes utilizados exclusivamente em microeletrônica, levou ao desenvolvimento de sensores físicos que hoje são onipresentes no dia-dia. Desses elementos, o cantilever, ou viga engastada, é a estrutura mais simples, porém, quando miniaturizado em escala micrométrica, suas propriedades mecânicas como frequência de ressonância e curvatura são muito sensíveis a eventos que ocorrem em sua superfície. Stresses superficiais mínimos, como aqueles gerados pela adsorção de monocamadas na superfície, causam deflexões em uma escala que é facilmente medida com técnicas relativamente simples. Além disso, a frequência de ressonância que é característica da estrutura, é proporcional à mudanças relativas de massa do dispositivo, sendo possível assim, a medida de massa em baixíssimas escalas. Nesse trabalho, estudou-se a utilização do microcantilever como uma plataforma para estudo de materiais, mais especificamente, materiais poliméricos. Depositando-se uma quantidade muito pequena de polímero na superfície de um microcantilever de silício, essa estrutura se curvará devido à diferenças nos coeficientes de expansão térmico entre os materiais. Medindo-se essa curvatura em função da temperatura, é possível detectar eventos térmicos que esse polímero venha sofrer. Esse efeito foi utilizado para estudar como a absorção de água afeta o evento térmico de transição vítrea do polímero PLGA. Observou-se que essa caracterização é muito mais rápida utilizando microcantilever se comparado às técnicas convencionais, além de ser também, muito sensível às variações de quantidade de água. Para a realização desses estudos, foi desenvolvido um sistema de medidas que utiliza pick-up de CDROM, retirada de um leitor comum, para medir a deflexão dos dispositivos. Esse tipo de arranjo é capaz de medir diferenças de nanômetros de deslocamento com um custo mínimo. Explorou-se a capacidade de controle de temperatura e leitura de deslocamento aplicando-se a técnica de modulação de temperatura nos estudos de eventos térmicos do PLGA. Observou-se que a modulação de temperatura é aplicável a esse tipo de medida e resultados muito semelhantes àqueles obtidos com técnicas convencionais são obtidos com uma quantidade muito menor de material. Como essas medidas foram realizadas utilizando sensores comerciais, realizamos a construção de matrizes de cantileveres no laboratório para demonstrar completo desenvolvimento desse tipo de plataforma de sensor. Empregando um polímero fotossensível relativamente novo para o desenvolvimento dessas matrizes, às utilizamos para caracterizações das propriedades mecânicas desse material. / The miniaturization of mechanical elements such as bridges or beams employing fabrication process previously used exclusively in microelectronics, resulted in the development of ubiquous physical sensors used today. The cantilever, or single supported beam is the most simple of these structures, but, when miniaturizated in the micrometer scale, the properties of the structure are highly dependent on events that takes place in its surface. Minimal superficial stresses like the ones generated by the adsorption of monolayers causes deflection of the structure in a scale that are easily measured by simple techniques. Moreover, the resonant frequency is highly dependent on relative mass changes of the device, making it a very sensitive microbalance. In this work, it was studied the application of microcantilevers as a platform for the study of materials properties, more specifically thermal analysis of polymeric material. When a very small quanitity of polymer is deposited in the surface of a silicon microcantilever, the structure will bend due to the mismatch of thermal expansion between the materials. Measuring the beam curvature in function of temperature enables the detection of thermal events suffered by the polymer. This effect was used to measure how the water absorption by the polymer affect the glass transition thermal event of the PLGA polymer. It was observed that this technique is faster if compared to traditional thermal chracterization techniques. To enable those characterizations, it was developed a measurement systems based on CDROM pick-up that can read the nanometer scale cantilever deflection with a minimum cost. The full capabilities of this system was then used to apply temperature modulation to the thermal studies of PLGA, we observed similar responses if compared to traditional approaches but with much less material use. Comercial sensors were used on these characterization, but, to present complet domain of cantilever sensor platform, we developed a fabrication process of polymeric cantilever array at the lab. These arrays were then used to extract mechanical information about the polymer used in its construction.

A miniaturização de elementos mecânicos como pontes e vigas por meio de processos de fabricação antes utilizados exclusivamente em microeletrônica, levou ao desenvolvimento de sensores físicos que hoje são onipresentes no dia-dia. Desses elementos, o cantilever, ou viga engastada, é a estrutura mais simples, porém, quando miniaturizado em escala micrométrica, suas propriedades mecânicas como frequência de ressonância e curvatura são muito sensíveis a eventos que ocorrem em sua superfície. Stresses superficiais mínimos, como aqueles gerados pela adsorção de monocamadas na superfície, causam deflexões em uma escala que é facilmente medida com técnicas relativamente simples. Além disso, a frequência de ressonância que é característica da estrutura, é proporcional à mudanças relativas de massa do dispositivo, sendo possível assim, a medida de massa em baixíssimas escalas. Nesse trabalho, estudou-se a utilização do microcantilever como uma plataforma para estudo de materiais, mais especificamente, materiais poliméricos. Depositando-se uma quantidade muito pequena de polímero na superfície de um microcantilever de silício, essa estrutura se curvará devido à diferenças nos coeficientes de expansão térmico entre os materiais. Medindo-se essa curvatura em função da temperatura, é possível detectar eventos térmicos que esse polímero venha sofrer. Esse efeito foi utilizado para estudar como a absorção de água afeta o evento térmico de transição vítrea do polímero PLGA. Observou-se que essa caracterização é muito mais rápida utilizando microcantilever se comparado às técnicas convencionais, além de ser também, muito sensível às variações de quantidade de água. Para a realização desses estudos, foi desenvolvido um sistema de medidas que utiliza pick-up de CDROM, retirada de um leitor comum, para medir a deflexão dos dispositivos. Esse tipo de arranjo é capaz de medir diferenças de nanômetros de deslocamento com um custo mínimo. Explorou-se a capacidade de controle de temperatura e leitura de deslocamento aplicando-se a técnica de modulação de temperatura nos estudos de eventos térmicos do PLGA. Observou-se que a modulação de temperatura é aplicável a esse tipo de medida e resultados muito semelhantes àqueles obtidos com técnicas convencionais são obtidos com uma quantidade muito menor de material. Como essas medidas foram realizadas utilizando sensores comerciais, realizamos a construção de matrizes de cantileveres no laboratório para demonstrar completo desenvolvimento desse tipo de plataforma de sensor. Empregando um polímero fotossensível relativamente novo para o desenvolvimento dessas matrizes, às utilizamos para caracterizações das propriedades mecânicas desse material. / The miniaturization of mechanical elements such as bridges or beams employing fabrication process previously used exclusively in microelectronics, resulted in the development of ubiquous physical sensors used today. The cantilever, or single supported beam is the most simple of these structures, but, when miniaturizated in the micrometer scale, the properties of the structure are highly dependent on events that takes place in its surface. Minimal superficial stresses like the ones generated by the adsorption of monolayers causes deflection of the structure in a scale that are easily measured by simple techniques. Moreover, the resonant frequency is highly dependent on relative mass changes of the device, making it a very sensitive microbalance. In this work, it was studied the application of microcantilevers as a platform for the study of materials properties, more specifically thermal analysis of polymeric material. When a very small quanitity of polymer is deposited in the surface of a silicon microcantilever, the structure will bend due to the mismatch of thermal expansion between the materials. Measuring the beam curvature in function of temperature enables the detection of thermal events suffered by the polymer. This effect was used to measure how the water absorption by the polymer affect the glass transition thermal event of the PLGA polymer. It was observed that this technique is faster if compared to traditional thermal chracterization techniques. To enable those characterizations, it was developed a measurement systems based on CDROM pick-up that can read the nanometer scale cantilever deflection with a minimum cost. The full capabilities of this system was then used to apply temperature modulation to the thermal studies of PLGA, we observed similar responses if compared to traditional approaches but with much less material use. Comercial sensors were used on these characterization, but, to present complet domain of cantilever sensor platform, we developed a fabrication process of polymeric cantilever array at the lab. These arrays were then used to extract mechanical information about the polymer used in its construction.

The work elucidates the novel physical and thermal properties of thin and ultra-thin films of crosslinked polymer and organized microstructures with a special emphasis on surface and interfacial effects and the structure-property relationships. Two major crosslinked polymer coatings have been thoroughly investigated: polymer microstructures fabricated by multi-laser interference lithography (IL), and plasma polymer coatings. We unveiled intriguing thermal properties of plasma polymer films originating from their physical state and exploiting the same for the design of ultrasensitve chemical sensors. A novel paradigm of surface coatings, single and bi-component periodic, porous crosslinked polymeric structures, has been introduced and thoroughly studied. Surface, interfacial, and mechanical properties of these novel class crosslinked polymer coatings clearly demonstrate the enormous potential of the IL microstructures as organized multicomponent polymer systems. When subjected to external or internal stresses the periodic porous structures can exhibit a sudden and dramatic pattern transformation resulting in remarkable change in the photonic, phononic and mechanical properties of these structures. Furthermore, the confinement of these instabilities to localized regions results in complex hierarchical structures. The two polymer coatings (plasma polymers and IL microstructures) with complementary attributes (such as periodic structure, vertical stratification, residual internal stresses, and high surface and interface tunability) enabled us to understand and design novel multifunctional polymer coatings.

Made available in DSpace on 2016-06-02T19:02:41Z (GMT). No. of bitstreams: 1 4784.pdf: 6177335 bytes, checksum: d4efe41cda16378eef382581c4b2c468 (MD5) Previous issue date: 2012-05-31 / Universidade Federal de Minas Gerais / The great interest to develop microcantilevers sensors is due to several desirable properties, in particular the ability to adjust the size and structure, thus increasing the perspectives for the construction of new sensor systems. In this work, we developed functionalized microcantilever sensors with conducting polymers to detect relative humidity, volatile organic compounds and insect pheromones. The development was based on a systematic investigation, since the polymer synthesis and the film formation until the sensing step. For this purpose, we studied two treatments to clean the microcantilevers surfaces (plasma and piranha solution). Also, appropriate ways for the sensors functionalization were evaluated, using spin-coating and thermoelastic probe techniques. The polyaniline solutions were obtained by the in-situ and interfacial synthesis. This way, the doping, morphology and the polymer structure have been investigated by the AFM, UV-Vis, FTIR, diffraction and FE-SEM techniques, and likewise the film properties. It allowed us to optimize the preparation conditions of the polyaniline films on the surface of the microcantilevers sensors to detect relative humidity and volatiles. Also, it was possible to develop sensors with polyaniline thin films, capable to detect 1 ppmv of relative humidity, and this shows that they can be used to measure large limits of detection. Moreover, the functionalized microcantilevers sensors showed a fast response time, repeatability over several cycles and exhibited lifetime longer than 6 months. The coated microcantilevers sensors showed an excellent response to the volatile organic compounds (VOCs), indicating that the sensitive layer was xiv appropriate for detection of these volatiles. The sensitivity of these sensors at VOCs increased with the polarity, thus the methanol compound showed the greatest sensitivity. It was possible to detect and evaluate different concentrations of the pheromone 2-heptanone, at different temperatures. The microcantilever sensors response not only showed an excellent sensitivity, but also a fast response time. It was observed an excellent response to deflection of the microcantilever sensors when exposed to volatile during the banana ripeness. / O grande interesse em desenvolver sensores de microcantilevers é devido às várias propriedades desejáveis, em particular a capacidade de adaptar o tamanho e a estrutura, aumentando, dessa forma, as perspectivas para a construção de novos sistemas de sensoriamento. Neste trabalho foram desenvolvidos nanossensores de microcantilever funcionalizados com polianilina, no estado de oxidação esmeraldina, para detecção de umidade relativa, de compostos orgânicos voláteis e, potenciais aplicações para detecção de feromônios de insetos e no amadurecimento de frutas. Para isso, o desenvolvimento se baseou em uma investigação sistemática, desde a síntese do polímero e a formação de filmes até a etapa de sensoriamento. Para tal, foram estudados dois tratamentos de limpeza das superfícies dos microcantilevers, o plasma e a solução piranha . Também foram avaliadas maneiras adequadas para a funcionalização dos sensores, empregando as técnicas de spin-coating, in-situ e sonda termoelástica à partir de soluções de polianilina obtidas pelas sínteses interfacial e in-situ, para a deposição de um filme fino em somente um lado da superfície do microcantilever. Dessa forma, a dopagem, cristalinidade e estrutura do polímero foram investigadas por meio das técnicas de UV-Vis, FTIR, difratometria e FE-MEV e, por conseguinte, as propriedades dos filmes. Estes estudos permitiram aperfeiçoar as condições de preparação dos filmes de polianilina sobre a superfície dos sensores de microcantilevers, para detecção de umidade relativa (%) e compostos orgânicos voláteis (COVs). Foi possível desenvolver sensores com filmes finos de polianilina, capazes de detectar umidade relativa até 1 ppmv, indicando, portanto, que os sensores xii desenvolvidos podem ser usados para medir grandes limites de detecção. Além disso, os sensores de microcantilevers funcionalizados apresentaram um tempo de resposta rápido, foram repetitivos a vários ciclos e apresentaram uma durabilidade maior que 6 meses. Os sensores de microcantilevers funcionalizados apresentaram uma excelente reposta aos COVs, indicando que a camada sensitiva foi adequada para detecção desses voláteis. A sensitividade dos sensores de microcantilever funcionalizados aos COVs aumentou com o aumento da polaridade do volátil, assim o composto que apresentou maior sensitividade foi o metanol. Foi possível avaliar e detectar diferentes concentrações do feromônio 2- heptanona em diferentes temperaturas. Os sensores mostraram uma excelente sensitividade e um tempo de resposta rápido. Foi observada uma excelente resposta de deflexão dos sensores de microcantilever quando expostos aos voláteis, durante o amadurecimento da banana.

No description available.

This thesis aims to measure the mechanical properties of ceramics on the microscale using microcantilever beams. Focussed Ion Beam milled triangular cross-sectional beams (approximately 3 x 5 x 20µm) were fractured using a nanoindenter to measure the Young’s modulus, fracture strength, and fracture toughness. By developing the technique with a sapphire bicrystal, it was found that the mechanical properties could be successfully ascertained if correction factors were used. Experiments and theoretical work showed that sapphire and polycrystalline alumina beams undergo moisture assisted sub-critical crack growth when tested in air. Whilst corrections for the Young’s modulus have been previously reported, this is the first reported attempt to correct for the notch tip residual stress and the first to consider sub-critical crack growth. Once these factors were characterised using the sapphire bicrystal, the technique was applied to a range of different ceramics, such as polycrystalline α-alumina and silicon nitride. These are the first reported direct measurements the grain boundary toughness of these ceramics using microcantilever beams. The grain boundary toughness was correlated with the macroscopic fracture properties and the characteristics of the ceramic (grain boundary composition, impurities, and fracture mode). Two grades of α-alumina were used and the macro- and micro-scale properties extensively compared. The damage evolution during uniaxial compression of alumina was investigated in depth, and compared to a previous reported microcrack evolution model using the measured grain boundary toughness. Investigation of whether deformation twins formed during loading was undertaken and the phenomenon was shown to not occur.