Este trabalho apresenta a modelagem comportamental desenvolvida para diferentes componentes necessários para a construção de uma microválvula eletromagneticamente atuável, associada ao uso de uma membrana flexível. Foram desenvolvidos modelos teóricos para a descrição do fluxo de fluidos em microcanais, especialmente canais com secções transversais retangulares, utilizadas na construção da maioria dos microcanais usados em microfluídica. O modelo para descrição da deformação experimentada por uma microponte de PDMS foi desenvolvido, permitindo estimar a rigidez elástica para diversas membranas desenvolvidas neste trabalho. Além disso um modelo teórico foi desenvolvido com o intuito de estudar as forças produzidas por uma microbobina com enrolamentos em formato espiral quadrado, sobre um imã permanente de NdFeB localizado em posições genéricas em relação à bobina. Utilizando o primeiro modelamento, estudo de microcanais, foi possível estimar a resistência hidráulica oferecida por microcanais com dimensões sub-milimétricas, permitindo avaliar a relação entre pressão de entrada e vazão de saída correspondente. Foi possível verificar analiticamente que para a faixa de trabalho especificada (vazões na faixa de 0,2 a 6 mL/min utilizando pressões na faixa de 0 a 30 kPa), canais com 1 cm de comprimento e 200 ?m de altura, devem possuir a largura variando na faixa de 300 µm a 500 µm de modo a operar na faixa de interesse estabelecida neste trabalho. Utilizando um canal com 2 cm de comprimento e 300 µm, o valor da altura pode estar entre 200 µm a 400 µm, permitindo miniaturizar o dispositivo final, garantindo a faixa de operação desejada. A partir da modelagem realizada com a finalidade de descrever o comportamento da membrana de PDMS, foi possível estimar teoricamente que uma membrana com 2 cm de comprimento, 2 mm de largura e a espessura variando na faixa de 1,6 a 2 mm, exige a realização de uma força na faixa de 10,5 mN a 13 mN (faixa para a força de atuação necessária), de modo a obter a deflexão de interesse neste trabalho (250 µm). Avaliando as microbobinas com base no modelo teórico desenvolvido neste trabalho, foi possível verificar que uma bobina contendo 36 enrolamentos, espaçamento de 80 µm, a uma distância de 1 mm do centro do imã, aplicando-se 10V (considerando uma resistência total de 100 Ohm), utilizando 10 camadas sobrepostas, é possível produzir uma força sobre um imã de NdFeB de até 0,18 N nas regiões de 3 mm a 10 mm afastadas em relação ao eixo x do imã, ainda a uma altura de 1 mm em relação ao plano xOy do imã. Após a fabricação dos componentes mencionados acima, foram propostos arranjos experimentais para a caracterização das respostas associadas a cada componente separadamente. As simulações apresentaram resultados similares aos obtidos experimentalmente, conforme pode ser avaliado visualizando os erros obtidos relacionando os resultados teóricos e experimentais, especialmente para os microcanais. Dispositivos microfluídicos foram fabricados obtendo canais com as seguintes dimensões: comprimento na faixa de 1 a 4 cm, largura na faixa de 100 a 400 µm e alturas na faixa de 200 a 600 µm, correspondentes à construção de 9 dispositivos com diferentes tamanhos, em que os 6 primeiros foram submetidos às análises experimentais sob as mesmas condições, repetidamente. Foi observado que tais microcanais foram capazes de fornecer até 1,41 mL/min a 0,8 kPa. O valor de vazão está dentro da faixa de desempenho do dispositivo (0,2 a 6 mL/min) com foco em sua aplicação na realização de análises químicas, onde as pressões fornecidas podem chegar até 60 kPa, fornecendo flexibilidade na produção de propulsão dos líquidos transportados através dos canais fabricados. Em relação aos resultados obtidos utilizando o modelo teórico para descrição do comportamento fluídico em microcanais, erros menores que 5% relativos aos resultados experimentais foram obtidos, indicando a validação do modelo teórico apresentado. Foram fabricados dispositivos com características comutadoras, normalmente abertas e normalmente fechadas, dependendo do método de fixação da membrana de PDMS ao substrato cerâmico. O projeto para o desenvolvimento de um chanfro na base do substrato cerâmico, na região de contato com a membrana de PDMS, foi desenvolvido com a finalidade de melhorar a selagem do canal com a válvula no estado fechado. Observou-se que para uma pressão de 5 kPa aplicada à entrada da válvula, não houve vazamento para os dispositivos normalmente fechados, e utilizando uma força em torno de 1 N é possível atingir taxas de fluxo de líquido da ordem de 0,45 mL/min, sendo esta superior às vazões necessárias para a aplicação em foco, qual seja, a automatização de microlaboratórios autônomos. Dois processos de montagem dos componentes para confecção das microválvulas foram desenvolvidos. Um deles visou a montagem da membrana de PDMS após a sinterização do sistema microfluídico junto à microbobina, e o outro visou a fixação da membrana antes da união entre o sistema e a bobina, necessitando de uma etapa de soldagem entre estes componentes após a fabricação das membranas junto ao substrato de LTCC. Microbobinas foram fabricadas com o intuito de realizar a atuação das microválvulas, a partir da atração/repulsão relacionada a um imã permanente de NdFeB (neodímio-ferro-boro) fixado à membrana flexível em contato com o canal. As bobinas foram fabricadas utilizando dimensões da ordem de 1 cm x 1 cm x 0,2 mm, apresentando de 15 a 44 enrolamentos, com gaps variando na faixa de 80 a 150 µm e as larguras dos fios condutores presente nos enrolamentos variando na faixa de 60 a 90 µm. Os resultados experimentais preliminares realizados demonstraram que uma bobina plana (uma camada, 36 enrolamentos, gap igual a 80 ?m, seção transversal de 1 cm x 1 cm), submetida a uma diferença de potencial de 1 V, é capaz de produzir uma força de 0,02 N sobre o imã permanente (localizado no centro a uma distância (no eixo z) de 1 mm da bobina). Este valor indica que para uma tensão de 10 V, devido a relação linear entre corrente e força magnética, utilizando até 10 camadas de bobinas sobrepostas, é possível obter esforços da ordem de 1 a 2 N (considerando a espessura do LTCC), permitindo que os dispositivos microfluídicos fabricados sejam acionados. / This work presents the physical modeling and implementation developed for different components necessary for the construction of electromagnetically actuating microvalves using a flexible membrane. Theoretical models were developed for describing the flow of fluids in microchannels, especially channels with rectangular transverse sections, routinely used as microchannels microfluidics. The model for the description of the deformation experienced by a PDMS microbridge was developed, allowing to estimate the elastic stiffness for various membranes developed in this work. In addition, a theoretical model was developed to study the forces produced by a microcoil with planar windings in squared spiral format, on a permanent magnet of NdFeB. Using the microchannel modeling, it was possible to estimate the hydraulic resistance offered by microchannels with micrometric dimensions, allowing to evaluate the relationship between inlet pressure and flow rate. It was possible to verify analytically that for the working range specified (flow rates of 0.2 to 6 mL/min for pressures from 0 to 30 kPa), channels with 1 cm in length and 200 ?m height should have a width varying in the range of 300 ?m to 500 µm in order to operate in the range of interest established in this study. Concerning the PDMS membrane, it was possible to estimate theoretically that a membrane with 2 cm in length, width of 2 mm and a thickness varying in the range of 1.6 to 2 mm, requires the implementation of a force in the range of 10.5 mN to 13 mN (range for the strength of action required) to obtain full deflection (250 µm). Evaluating Furthermore, using the theoretical model developed for the microcoils, it was possible to verify that a coil containing 36 windings, spacing of 80 µm, at a distance of 1 mm from the center of the magnet, and composed of 10 overlapping layers, it is possible to produce a force on a magnet of NdFeB up to 0.18 N in the regions from 3 mm to 10 mm away from the x-axis of the magnet, even at a height of 1 mm in relation to the plane xOy of magnet. The characterization of the responses associated with each component was made separately. The simulations showed similar results to those obtained experimentally, as evidenced from the errors obtained by relating the results of theoretical and experimental studies, especially for the microchannels. Microfluidic channels were manufactured with the following dimensions: length in the range of 1 to 4 cm, width in the range of 100 to 400 µm and heights in the range of 200 to 600 µm, 9 different devices were fabricated. It was observed that such microchannels were able to provide up to 1.41 mL/min to 0.8 kPa. The value of flow rate is within the expected range (0.2 to 6 mL/min) considering their application in chemical analysis, where the pressures provided can reach up to 60 kPa. Errors smaller than 5% for hydraulic resistance were obtained, indicating the validation of the theoretical model presented. Devices for fluidic switching with normally open and normally closed operation were fabricated and characterized with PDMS membranes and LTCC layers. Particularly a chamfer on the base of the ceramic substrates was proposed , in the region of contact with the membrane of PDMS, to better sealing the channel with the valve in a closed state. It has been observed that for a pressure of 5 kPa applied at the inlet of the valve, there was no leakage for the normally closed devices, and using a force around 1 N it is possible to achieve rates of liquid flow in the order of 0.45 mL/min, this being higher than the flow required for the intended application. Two assembling processes were developed for the microfluidic switching devices, one through the assembly of the PDMS membrane after LTCC sintering with the microcoil, and the other before the union between the switching device and the microcoil, requiring a step of welding between these components after the fabrication of membranes. Microcoils were manufactured and integrated with a NdFeB permanent magnet attached to a flexible membrane in contact with the channel. The coils were manufactured using dimensions of approximately 1 cm x 1 cm x 0.2 mm, containing 15 to 44 windings, with gaps ranging from 80 to 150 µm and the widths of the conductive wires in the range from 60 to 90 µm. The preliminary experimental results demonstrated that a planar coil (one layer, 36 windings, gap equal to 80 µm, cross section of 1 cm x 1 cm), subject to a potential difference of 1 Volt, is capable of producing a force of 0.02 N on the permanent magnet (located in the center at a z distance of 1 mm of the coil). This value indicates that at a voltage of 10 V it is possible to obtain a force of approximately 1 to 2 N for a coil with 10 layers, allowing for actuation of the microvalves developed.

Este trabalho apresenta a modelagem comportamental desenvolvida para diferentes componentes necessários para a construção de uma microválvula eletromagneticamente atuável, associada ao uso de uma membrana flexível. Foram desenvolvidos modelos teóricos para a descrição do fluxo de fluidos em microcanais, especialmente canais com secções transversais retangulares, utilizadas na construção da maioria dos microcanais usados em microfluídica. O modelo para descrição da deformação experimentada por uma microponte de PDMS foi desenvolvido, permitindo estimar a rigidez elástica para diversas membranas desenvolvidas neste trabalho. Além disso um modelo teórico foi desenvolvido com o intuito de estudar as forças produzidas por uma microbobina com enrolamentos em formato espiral quadrado, sobre um imã permanente de NdFeB localizado em posições genéricas em relação à bobina. Utilizando o primeiro modelamento, estudo de microcanais, foi possível estimar a resistência hidráulica oferecida por microcanais com dimensões sub-milimétricas, permitindo avaliar a relação entre pressão de entrada e vazão de saída correspondente. Foi possível verificar analiticamente que para a faixa de trabalho especificada (vazões na faixa de 0,2 a 6 mL/min utilizando pressões na faixa de 0 a 30 kPa), canais com 1 cm de comprimento e 200 ?m de altura, devem possuir a largura variando na faixa de 300 µm a 500 µm de modo a operar na faixa de interesse estabelecida neste trabalho. Utilizando um canal com 2 cm de comprimento e 300 µm, o valor da altura pode estar entre 200 µm a 400 µm, permitindo miniaturizar o dispositivo final, garantindo a faixa de operação desejada. A partir da modelagem realizada com a finalidade de descrever o comportamento da membrana de PDMS, foi possível estimar teoricamente que uma membrana com 2 cm de comprimento, 2 mm de largura e a espessura variando na faixa de 1,6 a 2 mm, exige a realização de uma força na faixa de 10,5 mN a 13 mN (faixa para a força de atuação necessária), de modo a obter a deflexão de interesse neste trabalho (250 µm). Avaliando as microbobinas com base no modelo teórico desenvolvido neste trabalho, foi possível verificar que uma bobina contendo 36 enrolamentos, espaçamento de 80 µm, a uma distância de 1 mm do centro do imã, aplicando-se 10V (considerando uma resistência total de 100 Ohm), utilizando 10 camadas sobrepostas, é possível produzir uma força sobre um imã de NdFeB de até 0,18 N nas regiões de 3 mm a 10 mm afastadas em relação ao eixo x do imã, ainda a uma altura de 1 mm em relação ao plano xOy do imã. Após a fabricação dos componentes mencionados acima, foram propostos arranjos experimentais para a caracterização das respostas associadas a cada componente separadamente. As simulações apresentaram resultados similares aos obtidos experimentalmente, conforme pode ser avaliado visualizando os erros obtidos relacionando os resultados teóricos e experimentais, especialmente para os microcanais. Dispositivos microfluídicos foram fabricados obtendo canais com as seguintes dimensões: comprimento na faixa de 1 a 4 cm, largura na faixa de 100 a 400 µm e alturas na faixa de 200 a 600 µm, correspondentes à construção de 9 dispositivos com diferentes tamanhos, em que os 6 primeiros foram submetidos às análises experimentais sob as mesmas condições, repetidamente. Foi observado que tais microcanais foram capazes de fornecer até 1,41 mL/min a 0,8 kPa. O valor de vazão está dentro da faixa de desempenho do dispositivo (0,2 a 6 mL/min) com foco em sua aplicação na realização de análises químicas, onde as pressões fornecidas podem chegar até 60 kPa, fornecendo flexibilidade na produção de propulsão dos líquidos transportados através dos canais fabricados. Em relação aos resultados obtidos utilizando o modelo teórico para descrição do comportamento fluídico em microcanais, erros menores que 5% relativos aos resultados experimentais foram obtidos, indicando a validação do modelo teórico apresentado. Foram fabricados dispositivos com características comutadoras, normalmente abertas e normalmente fechadas, dependendo do método de fixação da membrana de PDMS ao substrato cerâmico. O projeto para o desenvolvimento de um chanfro na base do substrato cerâmico, na região de contato com a membrana de PDMS, foi desenvolvido com a finalidade de melhorar a selagem do canal com a válvula no estado fechado. Observou-se que para uma pressão de 5 kPa aplicada à entrada da válvula, não houve vazamento para os dispositivos normalmente fechados, e utilizando uma força em torno de 1 N é possível atingir taxas de fluxo de líquido da ordem de 0,45 mL/min, sendo esta superior às vazões necessárias para a aplicação em foco, qual seja, a automatização de microlaboratórios autônomos. Dois processos de montagem dos componentes para confecção das microválvulas foram desenvolvidos. Um deles visou a montagem da membrana de PDMS após a sinterização do sistema microfluídico junto à microbobina, e o outro visou a fixação da membrana antes da união entre o sistema e a bobina, necessitando de uma etapa de soldagem entre estes componentes após a fabricação das membranas junto ao substrato de LTCC. Microbobinas foram fabricadas com o intuito de realizar a atuação das microválvulas, a partir da atração/repulsão relacionada a um imã permanente de NdFeB (neodímio-ferro-boro) fixado à membrana flexível em contato com o canal. As bobinas foram fabricadas utilizando dimensões da ordem de 1 cm x 1 cm x 0,2 mm, apresentando de 15 a 44 enrolamentos, com gaps variando na faixa de 80 a 150 µm e as larguras dos fios condutores presente nos enrolamentos variando na faixa de 60 a 90 µm. Os resultados experimentais preliminares realizados demonstraram que uma bobina plana (uma camada, 36 enrolamentos, gap igual a 80 ?m, seção transversal de 1 cm x 1 cm), submetida a uma diferença de potencial de 1 V, é capaz de produzir uma força de 0,02 N sobre o imã permanente (localizado no centro a uma distância (no eixo z) de 1 mm da bobina). Este valor indica que para uma tensão de 10 V, devido a relação linear entre corrente e força magnética, utilizando até 10 camadas de bobinas sobrepostas, é possível obter esforços da ordem de 1 a 2 N (considerando a espessura do LTCC), permitindo que os dispositivos microfluídicos fabricados sejam acionados. / This work presents the physical modeling and implementation developed for different components necessary for the construction of electromagnetically actuating microvalves using a flexible membrane. Theoretical models were developed for describing the flow of fluids in microchannels, especially channels with rectangular transverse sections, routinely used as microchannels microfluidics. The model for the description of the deformation experienced by a PDMS microbridge was developed, allowing to estimate the elastic stiffness for various membranes developed in this work. In addition, a theoretical model was developed to study the forces produced by a microcoil with planar windings in squared spiral format, on a permanent magnet of NdFeB. Using the microchannel modeling, it was possible to estimate the hydraulic resistance offered by microchannels with micrometric dimensions, allowing to evaluate the relationship between inlet pressure and flow rate. It was possible to verify analytically that for the working range specified (flow rates of 0.2 to 6 mL/min for pressures from 0 to 30 kPa), channels with 1 cm in length and 200 ?m height should have a width varying in the range of 300 ?m to 500 µm in order to operate in the range of interest established in this study. Concerning the PDMS membrane, it was possible to estimate theoretically that a membrane with 2 cm in length, width of 2 mm and a thickness varying in the range of 1.6 to 2 mm, requires the implementation of a force in the range of 10.5 mN to 13 mN (range for the strength of action required) to obtain full deflection (250 µm). Evaluating Furthermore, using the theoretical model developed for the microcoils, it was possible to verify that a coil containing 36 windings, spacing of 80 µm, at a distance of 1 mm from the center of the magnet, and composed of 10 overlapping layers, it is possible to produce a force on a magnet of NdFeB up to 0.18 N in the regions from 3 mm to 10 mm away from the x-axis of the magnet, even at a height of 1 mm in relation to the plane xOy of magnet. The characterization of the responses associated with each component was made separately. The simulations showed similar results to those obtained experimentally, as evidenced from the errors obtained by relating the results of theoretical and experimental studies, especially for the microchannels. Microfluidic channels were manufactured with the following dimensions: length in the range of 1 to 4 cm, width in the range of 100 to 400 µm and heights in the range of 200 to 600 µm, 9 different devices were fabricated. It was observed that such microchannels were able to provide up to 1.41 mL/min to 0.8 kPa. The value of flow rate is within the expected range (0.2 to 6 mL/min) considering their application in chemical analysis, where the pressures provided can reach up to 60 kPa. Errors smaller than 5% for hydraulic resistance were obtained, indicating the validation of the theoretical model presented. Devices for fluidic switching with normally open and normally closed operation were fabricated and characterized with PDMS membranes and LTCC layers. Particularly a chamfer on the base of the ceramic substrates was proposed , in the region of contact with the membrane of PDMS, to better sealing the channel with the valve in a closed state. It has been observed that for a pressure of 5 kPa applied at the inlet of the valve, there was no leakage for the normally closed devices, and using a force around 1 N it is possible to achieve rates of liquid flow in the order of 0.45 mL/min, this being higher than the flow required for the intended application. Two assembling processes were developed for the microfluidic switching devices, one through the assembly of the PDMS membrane after LTCC sintering with the microcoil, and the other before the union between the switching device and the microcoil, requiring a step of welding between these components after the fabrication of membranes. Microcoils were manufactured and integrated with a NdFeB permanent magnet attached to a flexible membrane in contact with the channel. The coils were manufactured using dimensions of approximately 1 cm x 1 cm x 0.2 mm, containing 15 to 44 windings, with gaps ranging from 80 to 150 µm and the widths of the conductive wires in the range from 60 to 90 µm. The preliminary experimental results demonstrated that a planar coil (one layer, 36 windings, gap equal to 80 µm, cross section of 1 cm x 1 cm), subject to a potential difference of 1 Volt, is capable of producing a force of 0.02 N on the permanent magnet (located in the center at a z distance of 1 mm of the coil). This value indicates that at a voltage of 10 V it is possible to obtain a force of approximately 1 to 2 N for a coil with 10 layers, allowing for actuation of the microvalves developed.

No description available.

No description available.

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No description available.

Complex flow structures consisting of branching, multi-scale, hierarchically arranged flow paths can be a beneficial in certain applications by providing lower hydraulic and thermal resistances than conventional flow arrangements. In this study, an experimental approach was used to investigate the hydrodynamic and thermal effects of the complexity, or degree of branching, in microscale complex flow structures. The primary focus of this work was to develop new concepts to advance the current capabilities of complex flow structures through management of complexity. The effects of complexity were determined from experiments performed on a set of microfluidic test sections which were identical except for the complexity of the underlying microchannel configuration. Comparison of the relative hydrodynamic and thermal performance indicates that complexity has a strong effect on both the pressure drop and heat transfer. When the pumping power is taken into account, the results suggest that higher complexity arrangements improve the overall thermal-hydraulic performance. This conclusion was confirmed by the trends observed in the coefficient of performance, a measure of the device thermal efficiency. To address the limitations of conventional fixed-complexity designs, the concept of a variable-complexity flow structure is developed. With a variable-complexity design, the configuration of a branched flow structure can be dynamically controlled to improve performance as operational conditions vary. This concept was successfully demonstrated by developing and testing an active variable-complexity microfluidic device in which pneumatically controlled microvalves were used to create different flow channel configurations. The variable-complexity concept was further refined by developing a microfluidic device with a passive variable-complexity design in which the flow channel configuration changed autonomously based on local temperatures. By using microvalves containing a temperature sensitive polymer, the flow configuration of the device was made thermally adaptive. Experiments were performed to characterize the behavior of the polymer microvalves and the overall device performance. The results showed that the device was capable of tracking changes in external heat sources by adapting and reconfiguring its internal flow structure. The experiments also showed how this variable-complexity design can reduce the pumping power expenditure by automatically directing flow only to areas where it is required. / text

UV-LIGA is a microfabrication process realzed by material deposition through microfabricated molds. UV photolithography is conducted to pattern precise thick micro molds using UV light sensitive materials, mostly SU-8, and electroforming is performed to fabricate micro metallic structures defined by the micro molds. Therefore, UV-LIGA is a bottom-up in situ material-addition process. UV-LIGA has received broad attention recently than LIGA – a micro molding fabrication process using X-ray to pattern the micro molds. LIGA is an expansive and is limited in access. In comparing to LIGA, the UV-LIGA is a cost effective process, and is widely accessible and safe. Therefore, it has been extensively used for the fabrication of metallic micro-electro-mechanical-systems (MEMS). The motivation of this research was to study micro mechanical systems fabricated with nano-structured metallic materials via UV-LIGA process. Various micro mechanical systems with high-aspect-ratio and thick metallic structures have been developed and are presented in this desertation. A novel micro mechanical valve has been developed with nano-structured nickel realized with UV-LIGA fabrication technique. Robust compact valves are crucial for space applications where payload and rubstaness are critically concerned. Two types of large flow rate robust passive micro check valve arrays have been designed, fabricated and tested for robust hydraulic actuators. The first such micro valve developed employs nanostructured nickel as the valve flap and single-crystal silicon as the substrates to house inlet and outlet channels. The Nano-structured nickel valve flap was fabricated using the UV-LIGA process developed and the microchannels were fabricated by deep reactive etching (DRIE) method. The valves were designed to operate under a high pressure (>10MPa), able to operate at high frequencies (>10kHz) in cooperating with the PZT actuator to produce large flow rates (>10 cc/s). The fabricated microvalves weigh 0.2 gram, after packing with a novel designated valve stopper. The tested results showed that the micro valve was able to operate at up to 14kHz. This is a great difference in comparison to traditional mechanical valves whose operations are limited to 500 Hz or less. The advantages of micro machined valves attribute to the scaling laws. The second type of micro mechanical valves developed is a in situ assembled solid metallic (nickel) valves. Both the valve substrates for inlet and outlet channels and the valve flap, as well as the valve stopper were made by nickel through a UV-LIGA fabrication process developed. Continuous multiple micro molds fabrication and molding processes were performed. Final micro mechanical valves were received after removing the micro molds used to define the strutures. There is no any additional machining process, such as cutting or packaging. The alignment for laminated fabrication was realized under microscope, therefore it is a highly precise in situ fabrication process. Testing results show the valve has a forward flow rate of19 cc/s under a pressure difference of 90 psi. The backward flow rate of 0.023 cc/s, which is negligible (0.13%). Nano-structured nickel has also been used to develop laminated (sandwiched) micro cryogenic heater exchanger with the UV-LIGA process. Even though nickel is apparently not a good thermal conductor at room temperature, it is a good conductor at cryogentic temerpature since its thermal conductivity increases to 1250 W/k·m at 77K. Micro patterned SU-8 molds and electroformed nickel have been developed to realize the sandwiched heat exchanger. The SU-8 mold (200mm x 200mm x50mm) array was successfully removed after completing the nickel electroforming. The second layer of patterned SU-8 layer (200mm x 200mm x50mm, as a thermal insulating layer) was patterned and aligned on the top of the electroformed nickel structure to form the laminated (sandwiched) micro heat exchanger. The fabricated sandwiched structure can withstand cryogenic temperature (77K) without any damages (cracks or delaminations). A study on nanocomposite for micro mechanical systems using UV-LIGA compatible electroforming process has been performed. Single-walled carbon nanotubes (SWNTs) have been proven excellent mechanical properties and thermal conductive properties, such as high strength and elastic modulus, negative coefficient of thermal expansion (CTE) and a high thermal conductivity. These properties make SWNT an excellent reinforcement in nanocomposite for various applications. However, there has been a challenge of utilizing SWNTs for engineering applications due to difficulties in quality control and handling – too small (1-2nm in diameter). A novel copper/SWNT nanocomposite has been developed during this dissertational research. The goal of this research was to develop a heat spreader for high power electronics (HPE). Semiconductors for HPE, such as AlGaN/GaN high electron mobility transistors grown on SiC dies have a typical CTE about 4~6x10-6/k while most metallic heat spreaders such as copper have a CTE of more than 10x10-6/k. The SWNTs were successfully dispersed in the copper matrix to form the SWNT/Cu nano composite. The tested composite density is about 7.54 g/cm3, which indicating the SWNT volumetric fraction of 18%. SEM pictures show copper univformly coated on SWNT (worm-shaped structure). The measured CTE of the nanocomposite is 4.7 x 10-6/°C, perfectly matching that of SiC die (3.8 x 10-6/°C). The thermal conductivity derived by Wiedemann-Franz law after measuring composit's electrical conductivity, is 588 W/m-K, which is 40% better than that of pure copper. These properties are extremely important for the heat spreader/exchanger to remove the heat from HPE devices (SiC dies). Meanwhile, the matched CTE will reduce the resulted stress in the interface to prevent delaminations. Therefore, the naocomposite developed will be an excellent replacement material for the CuMo currently used in high power radar, and other HPE devices under developing. The mechanical performance and reliability of micro mechanical devices are critical for their application. In order to validate the design & simulation results, a direct (tensile) test method was developed to test the mechanical properties of the materials involved in this research, including nickel and SU-8. Micro machined specimens were fabricated and tested on a MTS Tytron Micro Force Tester with specially designed gripers. The tested fracture strength of nanostructured nickel is 900±70 MPa and of 50MPa for SU-8, resepctively which are much higher than published values.

A wide variety of nanomaterials ranging from polymer assemblies to organic and inorganic nanostructures (particles, wires, rods etc) have been actively pursued in recent years for various applications. The synthesis route of these nanomaterials had been driven through two fundamental approaches - 'Top down' and 'Bottom up'. The key aspect of their application remained in the ability to make the nanomaterials suitable for targeted location by manipulating their structure and functionalizing with active target groups. Functional nanomaterials like polyelectrolyte based multilayered thin films, nanofibres and graphene based composite materials are highlighted in the current research. Multilayer thin films were fabricated by conventional dip coating and newly developed spray coating techniques. Spray coating technique has an advantage of being applied for large scale production as compared to the dip coating technique. Conformal hydrophobic/hydrophilic and superhydrophobic/hydrophilic thermal switchable surfaces were fabricated with multilayer films of poly(allylaminehydrochloride) (PAH) and silica nanoparticles by the dip coating technique, followed by the functionalization with thermosensitive polymer-poly(N-isopropylacrylamide)(PNIPAAM) and perfluorosilane. The thermally switchable superhydrophobic/ hydrophilic polymer patch was integrated in a microfluidic channel to act as a stop valve. At 70 degree centigrade, the valve was superhydrophobic and stopped the water flow (close status) while at room temperature, the patch became hydrophilic, and allowed the flow (open status). Spray-coated multilayered film of poly(allylaminehydrochloride) (PAH) and silica nanoparticles was fabricated on polycarbonate substrate as an anti-reflection (AR) coating. The adhesion between the substrate and the coating was enhanced by treating the polycarbonate surface with aminopropyltrimethoxylsilane (APTS) and sol-gel. The coating was finally made abrasion-resistant with a further sol-gel treatment on top of AR coating, which formed a hard thin scratch-resistant film on the coating. The resultant AR coating could reduce the reflection from 5 to 0.3% on plastic. Besides multilayered films, the fabrication of polyelectrolyte based electrospun nanofibers was also explored. Ultrathin nanofibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylaminehydrochloride) (PAH) were fabricated using the electrospinning technique and methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. The fiber was also loaded with a real life anti-depressant drug (2,3-tertbutyl-4-methoxyphenol) and fiber surface was made superhydrophobic. The drug loaded superhydrophobic nanofiber mat was immersed under water, phosphate buffer saline and surfactant solutions in three separated experiments. The rate of release of durg was monitored from the fiber surface as a result of wetting with different solutions. Time dependent wetting of the superhydrophobic surface and consequently the release of drug was studied with different concentrations of surfactant solutions. The results provided important information about the underwater superhydrophobicity and retention time of drug in the nanofibers. The nanostructured polymers like nanowires, nanoribbons and nanorods had several other applications too, based on their structure. Different self-assembled structures of semiconducting polymers showed improved properties based on their architectures. Poly(3-hexylthiophene) (P3HT) supramolecular structures were fabricated on P3HT-dispersed reduced graphene oxide (RGO) nanosheets. P3HT was used to disperse RGO in hot anisole/N, N-dimethylformamide solvents, and the polymer formed nanowires on RGO surfaces through a RGO induced crystallization process. The Raman spectroscopy confirmed the interaction between P3HT and RGO, which allowed the manipulation of the composite's electrical properties. Such a bottom-up approach provided interesting information about graphene-based composites and inspired to study the interaction between RGO and the molecular semiconductor-tetrasulphonate salt of copper phthalocyanine (TSCuPc) for nanometer-scale electronics. The reduction of graphene oxide in presence of TSCuPc produced a highly stabilized aqueous composite ink with monodispersed graphene sheets. To demonstrate the potential application of the donor (TSCuPc)'acceptor (graphene) composite, the RGO/TSCuPc suspension was successfully incorporated in a thin film device and the optoelectronic property was measured. The conductivity (dark current) of the composite film decreased compared to that of pure graphene due to the donor molecule incorporation, but the photoconductivity and photoresponsivity increased to an appreciable extent. The property of the composite film overall improved with thermal annealing and optimum loading of TSCuPc molecules.

This thesis presents analysis, design, implementation, and testing of electrostatically actuated MEMS microvalves. The microvalves are specifically designed for lab-on-a-chip applications to achieve leakage ratios below 0.1 at pressure levels in the order of 101 kPa. For this purpose, two different microvalves are presented in the study. In the proposed designs, electrostatic actuation scheme is utilized to operate the microvalves in normally open and normally closed modes. Characterization of normally open microvalves show that, microvalves with radii ranging between 250