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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Copolímeros à base de estireno e anidrido maleico: caracterização e estudo viscosimétrico / Copolymers based on styrene and maleic anhydride: viscosimetric studies an characterization

Alexandre Andrade de Souza Costa 17 January 2014 (has links)
Copolímeros à base de estireno e anidrido maleico (SMA) são materiais sintéticos comercialmente disponíveis, obtidos pela reação dos dois monômeros citados em diferentes proporções, resultando em materiais versáteis, e disponíveis em diferentes graus de massas e porcentagens molares de anidrido maleico. São considerados polímeros funcionais devido à reatividade do grupamento anidrido maleico presente na cadeia polimérica. Por este motivo, esses materiais possuem vasta gama de aplicações, e elevada importância em diversas áreas, principalmente por terem baixa toxicidade, boa resistência térmica e boa estabilidade dimensional. Dessa forma, para melhor aplicação desses copolímeros, é muito importante o conhecimento dos parâmetros relativos ao seu comportamento em solução. A viscosimetria, em especial, é um método simples, útil e apropriado para fornecer essas informações. Os parâmetros viscosimétricos podem ser matematicamente calculados por extrapolação gráfica, entretanto a geração dos dados experimentais é mais demorada. Em contrapartida, é possível que a determinação experimental seja feita de forma mais rápida, por um único ponto, procedimento esse que desperta tanto o interesse acadêmico quanto o industrial. Neste trabalho, foram empregados os dois métodos de cálculo, utilizando solventes puros, misturas de solventes e três amostras de copolímeros à base de SMA. As determinações foram conduzidas a 40C. Os copolímeros utilizados possuiam teores de anidrido maleico de 50%, 45% e 40%, sendo os dois últimos esterificados com butil-metil-éster e sec-butil-metil-éster, respectivamente. Os solventes utilizados foram: N-metil-pirrolidona (NMP), tetrahidrofurano (THF) e suas respectivas misturas 1:1 com metil-etil-cetona (MEK), ou seja, (NMP:MEK) e THF:MEK, sendo a MEK um não solvente para o copolímero não esterificado. As equações utilizadas para extrapolação gráfica foram as de Huggins, Kraemer e Schulz-Blaschke. As equações empregadas em um único ponto foram as de Solomon-Ciuta, Deb-Chanterjee e novamente Schulz-Blaschke. Os resultados obtidos foram comparados e avaliou-se a possibilidade da utilização do método mais rápido, por um único ponto, para os sistemas estudados através dos desvios percentuais tendo como padrão os resultados da equação de Huggins. A equação de Deb-Chanterjee foi a mais adequada aos sistemas em NMP, que foi também o melhor solvente para as amostras. Os resultados obtidos na mistura NMP:MEK sugeriram que a viscosimetria pode ter sido um método sensível às pequenas diferenças estruturais entre os grupos pendentes nas amostras esterificadas. Paralelamente, realizou-se análises de espectroscopia na região do infravermelho (FTIR), análise termogravimétrica (TGA) e ensaios dinâmico-mecânicos (DMA) para a caracterização estrutural e térmica das amostras. Somente os resultados obtidos a partir de DMA indicaram diferenças entre as amostras esterificadas / Styrene maleic anhydride copolymers (SMA) are synthetic materials commercially available, obtained by the reaction of styrene with maleic anhydride, resulting in very versatile products obtained in a wide range of molar masses and maleic anhydride proportions. The copolymers are considered to be functional due to maleic anhydride reactivity, that provides a very large range of applications, and major importance in different areas, mainly for the low toxicity, good thermal resistance and excellent dimensional stability. Thus, for improving the application of these materials, it is necessary and important to understand the behavior of the copolymers in solution. Therefore, viscosimetry can be a simple, helpful and suitable method to provide these informations. The viscosimetric parameters are generally mathematically calculated by graphic extrapolation. However, the experiments take too long. Indeed, it is possible to reduce the time of the execution by employing a single point determination. In this work, both calculation methods were performed, using pure solvents and mixtures and three different copolymers samples, based on SMA. The tests were carried out at 40oC. The copolymers contained 50%, 45% and 40% of maleic anhydride groups and the last two copolymers were esterified with butyl-methyl ester and sec-butyl-methyl ester. N-methyl-pyrrolidone (NMP), tetrahydrofuran (THF), and their mixtures (1:1) with methyl-ethyl-cetone (MEK) were employed as solvents. The latter was a non-solvent for the esterified copolymers. The equations applied for graphic extrapolation were Huggins, Kraemer and Schulz-Blaschke. The equations employed for a single point determination were Solomon-Ciuta, Deb-Chanterjee and again Schulz-Blaschke. The single point determination method values were compared with those obtained from Huggins equation, and the possibility of using the faster method was evaluated by analyzing percentage deviation. Deb-Chanterjee equation was the most adequate to the copolymers in NMP, which was the best solvent for the samples. The results obtained in NMP:MEK mixture suggested that viscosimetry could be a sensitive method to the small structural variations between the pendant groups in the esterified samples. The copolymers were structurally characterized by infrared spectroscopy (FTIR), and thermally by thermogravimetric analysis (TGA) and dynamic-mecanical analysis (DMA). The results obtained from those techniques did not show significant differences between the esterified copolymers, except for DMA
42

Estudo de sondas orgânicas e estratégias de marcação fluorescente de DNA: da fotoquímica básica à microscopia óptica de super-resolução / Study of organic probes and strategies for DNA fluorescent labelling: From basic photochemistry to super-resolution optical microscopy

Milena Helmer Lauer 12 May 2016 (has links)
A microscopia de fluorescência é uma das técnicas mais poderosas disponíveis atualmente, uma vez que proporciona uma combinação excepcional de alta sensibilidade na detecção, alta especificidade, além de ser consideravelmente não invasiva. Avanços recentes permitiram a detecção em resolução de subdifração, o que eleva sua potencialidade de investigação de um maior número de sistemas e, consequentemente, de avanço científico. O estudo de novas sondas fluorescentes é de fundamental importância para a aplicação em métodos avançados de microscopia óptica. Na primeira vertente da pesquisa, Capítulo 2, foi realizado o estudo fotofísico de uma série de compostos bisarilados derivados do anidrido maleico e de maleimidas sintetizados pela reação de Heck-Matsuda. Visando o aprimoramento do design dessas moléculas, foi realizada a ciclização fotoquímica de tais compostos, resultando em moléculas com anéis condensados, nomeados como derivados de fenantreno, as quais proporcionaram maior estabilidade fotoquímica. A dinâmica do estado excitado remete ao efeito push-pull, em que há um deslocamento de carga notável, mas não completo. Para os compostos com a substituição 4-hidroxifenil foi observado um processo de deslocamento de carga combinado com uma transferência de próton no estado excitado assistida por solvente. Ademais, o estudo dos compostos derivados de fenantreno em microscopia confocal demonstrou que as propriedades locais do solvente afetam a dinâmica de relaxação de fluorescência em diferentes meios condensados e que os mesmos são passíveis de serem aplicados a técnicas avançadas de microscopia de fluorescência. A segunda vertente desta tese, Capítulo 3, explora um sistema biológico em nível de uma única molécula. Especificamente, este capítulo concerne à investigação de uma metodologia ótima para a marcação fluorescente de DNA em sequência específica, através de microscopia de fluorescência com super-resolução. As reações foram conduzidas utilizando uma metodologia de marcação de duas etapas, de acordo com o princípio mTAG. Na primeira etapa, grupamentos contendo alquino terminal, azida ou amina primária são transferidos do cofator análogo ao S-adenosil-L-metionina para o DNA através de uma enzima metiltransferase. Foi utilizada a enzima M.TaqI, a qual tem como alvo a sequência 5\'- TGCA -3\' para modificação. Na segunda etapa é realizado o acoplamento do fluoróforo aos sítios funcionais do plasmídeo (pUC19) através de reações químicas bioortogonais, tais como reação click catalisada por cobre (CuAAC), reação click na ausência de cobre (SPAAC) e acoplamento do grupo amina primária com NHS-éster. Também foi desenvolvida uma metodologia direta de uma etapa, na qual o fluoróforo é diretamente transferido do cofator análogo para o DNA em uma única etapa reacional. Para acompanhar o desempenho das reações foi desenvolvido um ensaio single-molecule para a contagem do número de moléculas de corante ligadas a plasmídeos individuais. A topologia dos plasmídeos após a marcação foi investigada por imagens de AFM em alta resolução. A combinação de ambas as análises demonstrou que a reação SPAAC assim como a reação direta de uma etapa promoveram uma marcação fluorescente quase completa e a técnica de AFM confirmou que o acoplamento de fluoróforos não induziu danos à estrutura dos plasmídeos, os quais preservaram sua morfologia nativa, superenrolada. Além disso, os plasmídeos marcados foram aplicados com sucesso a procedimentos de transfecção em células de mamíferos, indicando que o DNA reteve sua capacidade de codificar informação genética, mesmo na presença de fluoróforos ligados. / Fluorescence microscopy is one of the most powerful techniques currently available, since it provides the unique combination of a high sensitivity in detection, a high specificity, and a considerable non-invasiveness. Recent developments have allowed the detection at a sub-diffraction resolution, which elevates its potentiality to investigate several systems and hence to go further in science. The study of new fluorescent probes is crucial for the application in advanced methods in optical microscopy. In the first extent of this research, Chapter 2, a photophysical study of maleic anhydride and maleimide derivatives, synthesized by the Heck-Matsuda reaction, was performed. Aiming at the improvement of the design of these molecules, a photochemical cyclization was carried out, resulting in molecules with condensed rings, termed as phenanthrene derivatives, which promoted more photochemical stability. The excited state dynamics rely on the push-pull effect, in which a notable, but not complete, charge shift takes place. For the compounds with a 4-hydroxyl substituent, a charge shift combined with an excited state solvent-assisted proton transfer was observed. Additionally, the confocal microscopy study of the phenanthrene derivatives showed that the local properties of the solvent modulate the fluorescence relaxation dynamics in condensed media and hence such dyes can be potential candidates for use in advanced fluorescence microscopy techniques. The second extent of this thesis, Chapter 3, explores a biological system at the single-molecule level. Specifically, this chapter concerns to an investigation of an optimal sequence-specific DNA fluorescent labelling, using super-resolution fluorescence microscopy. The reactions were performed using a two-step methodology, according to the mTAG approach. In the first step, moieties containing a terminal alkyne, azide, or primary amine group are transferred from an S-adenosyl-L-methionine analogue cofactor to the DNA by a methyltransferase enzyme. Herein, the enzyme M.TaqI was used, which targets the 5\'- TCGA -3\' sequence for modification. In the second step, a fluorophore is coupled to the functional sites of the plasmid (pUC19) using bio orthogonal reactions, such as the click reaction catalysed by copper (CuAAC), the copper-free click reaction (SPAAC), and the amino-to-NHS-ester coupling reaction. A direct one-step approach in which the fluorophore is directly transferred to the DNA from the analogue cofactor in a single reaction step, was also developed. A single-molecule assay was developed for counting the number of fluorophores associated with the individual plasmids. The topology of the plasmids after labelling was also investigated by high-resolution AFM imaging. Combining both analysis, the SPAAC as well as the direct one-step reactions were found to promote near-complete labelling and the AFM showed that the fluorophore coupling did not damage the structure of the plasmids and that their native, supercoiled, morphology was preserved. Moreover, labelled plasmids were successfully applied for transfection into mammalian cells, implying that the DNA retained its ability to encode genetic information, even while carrying bound fluorophores.
43

Copolímeros à base de estireno e anidrido maleico: caracterização e estudo viscosimétrico / Copolymers based on styrene and maleic anhydride: viscosimetric studies an characterization

Alexandre Andrade de Souza Costa 17 January 2014 (has links)
Copolímeros à base de estireno e anidrido maleico (SMA) são materiais sintéticos comercialmente disponíveis, obtidos pela reação dos dois monômeros citados em diferentes proporções, resultando em materiais versáteis, e disponíveis em diferentes graus de massas e porcentagens molares de anidrido maleico. São considerados polímeros funcionais devido à reatividade do grupamento anidrido maleico presente na cadeia polimérica. Por este motivo, esses materiais possuem vasta gama de aplicações, e elevada importância em diversas áreas, principalmente por terem baixa toxicidade, boa resistência térmica e boa estabilidade dimensional. Dessa forma, para melhor aplicação desses copolímeros, é muito importante o conhecimento dos parâmetros relativos ao seu comportamento em solução. A viscosimetria, em especial, é um método simples, útil e apropriado para fornecer essas informações. Os parâmetros viscosimétricos podem ser matematicamente calculados por extrapolação gráfica, entretanto a geração dos dados experimentais é mais demorada. Em contrapartida, é possível que a determinação experimental seja feita de forma mais rápida, por um único ponto, procedimento esse que desperta tanto o interesse acadêmico quanto o industrial. Neste trabalho, foram empregados os dois métodos de cálculo, utilizando solventes puros, misturas de solventes e três amostras de copolímeros à base de SMA. As determinações foram conduzidas a 40C. Os copolímeros utilizados possuiam teores de anidrido maleico de 50%, 45% e 40%, sendo os dois últimos esterificados com butil-metil-éster e sec-butil-metil-éster, respectivamente. Os solventes utilizados foram: N-metil-pirrolidona (NMP), tetrahidrofurano (THF) e suas respectivas misturas 1:1 com metil-etil-cetona (MEK), ou seja, (NMP:MEK) e THF:MEK, sendo a MEK um não solvente para o copolímero não esterificado. As equações utilizadas para extrapolação gráfica foram as de Huggins, Kraemer e Schulz-Blaschke. As equações empregadas em um único ponto foram as de Solomon-Ciuta, Deb-Chanterjee e novamente Schulz-Blaschke. Os resultados obtidos foram comparados e avaliou-se a possibilidade da utilização do método mais rápido, por um único ponto, para os sistemas estudados através dos desvios percentuais tendo como padrão os resultados da equação de Huggins. A equação de Deb-Chanterjee foi a mais adequada aos sistemas em NMP, que foi também o melhor solvente para as amostras. Os resultados obtidos na mistura NMP:MEK sugeriram que a viscosimetria pode ter sido um método sensível às pequenas diferenças estruturais entre os grupos pendentes nas amostras esterificadas. Paralelamente, realizou-se análises de espectroscopia na região do infravermelho (FTIR), análise termogravimétrica (TGA) e ensaios dinâmico-mecânicos (DMA) para a caracterização estrutural e térmica das amostras. Somente os resultados obtidos a partir de DMA indicaram diferenças entre as amostras esterificadas / Styrene maleic anhydride copolymers (SMA) are synthetic materials commercially available, obtained by the reaction of styrene with maleic anhydride, resulting in very versatile products obtained in a wide range of molar masses and maleic anhydride proportions. The copolymers are considered to be functional due to maleic anhydride reactivity, that provides a very large range of applications, and major importance in different areas, mainly for the low toxicity, good thermal resistance and excellent dimensional stability. Thus, for improving the application of these materials, it is necessary and important to understand the behavior of the copolymers in solution. Therefore, viscosimetry can be a simple, helpful and suitable method to provide these informations. The viscosimetric parameters are generally mathematically calculated by graphic extrapolation. However, the experiments take too long. Indeed, it is possible to reduce the time of the execution by employing a single point determination. In this work, both calculation methods were performed, using pure solvents and mixtures and three different copolymers samples, based on SMA. The tests were carried out at 40oC. The copolymers contained 50%, 45% and 40% of maleic anhydride groups and the last two copolymers were esterified with butyl-methyl ester and sec-butyl-methyl ester. N-methyl-pyrrolidone (NMP), tetrahydrofuran (THF), and their mixtures (1:1) with methyl-ethyl-cetone (MEK) were employed as solvents. The latter was a non-solvent for the esterified copolymers. The equations applied for graphic extrapolation were Huggins, Kraemer and Schulz-Blaschke. The equations employed for a single point determination were Solomon-Ciuta, Deb-Chanterjee and again Schulz-Blaschke. The single point determination method values were compared with those obtained from Huggins equation, and the possibility of using the faster method was evaluated by analyzing percentage deviation. Deb-Chanterjee equation was the most adequate to the copolymers in NMP, which was the best solvent for the samples. The results obtained in NMP:MEK mixture suggested that viscosimetry could be a sensitive method to the small structural variations between the pendant groups in the esterified samples. The copolymers were structurally characterized by infrared spectroscopy (FTIR), and thermally by thermogravimetric analysis (TGA) and dynamic-mecanical analysis (DMA). The results obtained from those techniques did not show significant differences between the esterified copolymers, except for DMA
44

Steric Stabilization of Polylactide particles achieved by Covalent 'grafting-from' with Hydrophilic Polymers

Nugroho, Robertus Wahyu Nayan January 2013 (has links)
Despite numerous advantages of using particles in a wide range of applications, they have one drawback that is their tendency to agglomerate. One way to overcome this problem is to sterically  stabilize the particles by introducing polymeric  chains covalently attached to the surface. Surface modification by covalently attaching polymer chains to the particle surface can be achieved by e.g. a ‘grafting-from’ technique under UV irradiation. In this thesis, polylactide (PLA) particles were surface modified, under UV irradiation, with the hydrophilic monomers: acrylamide (AAm), acrylic acid (AA), and maleic anhydride (MAH). The developed ‘grafting-from’ technique was shown to be nondestructive method for surface modification of PLA particles of two different geometries. The change in surface chemistry of the PLA particles was confirmed by FTIR and XPS, indicating the success of the surface grafting technique. Force interaction between two surface grafted PLA substrates was measured by colloidal probe AFM in different salt concentrations. In order to understand the repulsive force, the AFM force profiles were compared to the DLVO theory and AdG model. Long range repulsive interactions were mainly observed when hydrophilic polymers were covalently attached to the surface of PLA particles, leading to steric interaction. Attractive force dominated the interaction when neat PLA particle was approaching each other, resulting in particle aggregation, even though short range repulsion was observed at small separation distance, i.e. approximately 10 nm. Attractive interaction was also observed when neat PLA was approaching to PAA-grafted PLA substrate. This attractive interaction was much greater than force interaction between two neat PLA substrates.  The surface grafted particles can be used in biomedical application where secondary interactions are important to overcome particle agglomeration such as particle-based drug delivery. / <p>QC 20130529</p>
45

Caracterização vibracional e térmica de compósitos de LLDPES modificados e sílica (OU) Caracterização vibracional e térmica de compósitos de lldpe\'s funcionallzados e sílica de superfície modificada / Vibrational and thermal characterization of functionalized LLDPE composites and surface-modified silica

Santos, Ednardo Moreira 27 April 2006 (has links)
Compósitos de polímeros de polietileno linear de baixa densidade (LLDPE) possuem baixo desempenho mecânico devido principalmente à sua fraca interação, intermolecular, entre a cadeia polimérica e a carga. Uma maneira de minimizar esse baixo desempenho mecânico se faz com a mudança da estrutura química da poliolefina com a inserção de um grupo polar a sua cadeia, ou seja, faz-se a funcionalização das poliolefinas. O sistema de funcionalização adotado foi o processamento reativo, no qual foi utilizado para este sistema de processamento o misturador de dupla rosca acoplado a um reâmetro de torque. Neste trabalho, os grupos polares inseridos à cadeia dos polímeros de LLDPE\'s de copolímeros 1-buteno e 1-octeno (LLDPE-but e LLDPE-oct) foram o anidrido maléico (AM) e o anidrido tetrahidroftálico (ATF). Para a confecção dos compósitos foram utilizadas as cargas de microesferas de sílica modificada, no qual foi inserido compostos silanados em sua superfície (3-aminopropilsilano - APS - e trimetoxiclorosilano TMCISi) para estudo de interação com as poliolefinas funcionalizadas. Neste trabalho foram realizados ensaios de caracterização térmica, vibracional além de análises de torque do polímero fundido, análises do grau de reticulação e ensaios mecânicos de tração por elongação. Na caracterização térmica foram utilizadas as técnicas: termogravimetria (TG) e calorimetria exploratória diferencial (DSC). Na caracterização vibracional utilizou-se a espectroscopia fotoacústica no infravermelho (PAS-IR) e a espectroscopia de espalhamento Raman. Pela técnica PAS-IR foi possível comprovar a inserção dos anidridos à cadeia das poliolefinas assim como foi possível verificar a interação entre o polímero funcionalizado e a carga. Pelas técnicas térmicas de DSC e TG foi possível verificar mudanças das propriedades do compósito frente aos polímeros originais ou funcionalizados. Os ensaios mecânicos comprovaram que os compósitos de polímeros funcionalizados possuem maior elongação e tensão à ruptura comparada aos compósitos dos LLDPE\'s não funcionalizados / Linear low density composites have a weak mechanical behavior due mainly to the weak interactions - intermolecular - between the polymeric back bone and the charge. The anchoring a polar group in polymeric back bone is a strategy to increase the interactions between the polymer and the charge, as mean, the polyolefin is functionalized. The functionalization process used is the reactive process by a Mixer coupled with torque rheometer. In this work the polar groups used to functionalize the LLDPE\'s with comonomer 1-buten and 1-octen are maleic anhydride and tetrahydrophtalic anhydride. The composites were maked adding in to graft LLDPE\'s the charge of modified surface silicate micro-spheres whith 3aminepropylsilane or trimethoxyclorinesilane. This work to composites characterization was used thermal and vibrational characterization, and torque, crystalinity degree and mechanical tests. In thermal characterizations were used: termogravimetry (TG) and differential scanning calorimetry (DSC). In the vibrational characterization, the photoacoustic spectroscopy (PAS-IR) and Raman spectroscopy were used. Using the PAS-IR technique it was possible to prove the anhydride bonding in the polyolefin back bones, and also was possible verify the interactions between the functionalized polymer and the charge. With DSC and TG techniques was possible verify changes in composites properties in comparison to originais or functionalized polymers. The mechanical tests show that the functionalized polymer composites have bigger values of elongation and tensile strength in comparison to non functionalized LLDPE composites.
46

Caracterização vibracional e térmica de compósitos de LLDPES modificados e sílica (OU) Caracterização vibracional e térmica de compósitos de lldpe\'s funcionallzados e sílica de superfície modificada / Vibrational and thermal characterization of functionalized LLDPE composites and surface-modified silica

Ednardo Moreira Santos 27 April 2006 (has links)
Compósitos de polímeros de polietileno linear de baixa densidade (LLDPE) possuem baixo desempenho mecânico devido principalmente à sua fraca interação, intermolecular, entre a cadeia polimérica e a carga. Uma maneira de minimizar esse baixo desempenho mecânico se faz com a mudança da estrutura química da poliolefina com a inserção de um grupo polar a sua cadeia, ou seja, faz-se a funcionalização das poliolefinas. O sistema de funcionalização adotado foi o processamento reativo, no qual foi utilizado para este sistema de processamento o misturador de dupla rosca acoplado a um reâmetro de torque. Neste trabalho, os grupos polares inseridos à cadeia dos polímeros de LLDPE\'s de copolímeros 1-buteno e 1-octeno (LLDPE-but e LLDPE-oct) foram o anidrido maléico (AM) e o anidrido tetrahidroftálico (ATF). Para a confecção dos compósitos foram utilizadas as cargas de microesferas de sílica modificada, no qual foi inserido compostos silanados em sua superfície (3-aminopropilsilano - APS - e trimetoxiclorosilano TMCISi) para estudo de interação com as poliolefinas funcionalizadas. Neste trabalho foram realizados ensaios de caracterização térmica, vibracional além de análises de torque do polímero fundido, análises do grau de reticulação e ensaios mecânicos de tração por elongação. Na caracterização térmica foram utilizadas as técnicas: termogravimetria (TG) e calorimetria exploratória diferencial (DSC). Na caracterização vibracional utilizou-se a espectroscopia fotoacústica no infravermelho (PAS-IR) e a espectroscopia de espalhamento Raman. Pela técnica PAS-IR foi possível comprovar a inserção dos anidridos à cadeia das poliolefinas assim como foi possível verificar a interação entre o polímero funcionalizado e a carga. Pelas técnicas térmicas de DSC e TG foi possível verificar mudanças das propriedades do compósito frente aos polímeros originais ou funcionalizados. Os ensaios mecânicos comprovaram que os compósitos de polímeros funcionalizados possuem maior elongação e tensão à ruptura comparada aos compósitos dos LLDPE\'s não funcionalizados / Linear low density composites have a weak mechanical behavior due mainly to the weak interactions - intermolecular - between the polymeric back bone and the charge. The anchoring a polar group in polymeric back bone is a strategy to increase the interactions between the polymer and the charge, as mean, the polyolefin is functionalized. The functionalization process used is the reactive process by a Mixer coupled with torque rheometer. In this work the polar groups used to functionalize the LLDPE\'s with comonomer 1-buten and 1-octen are maleic anhydride and tetrahydrophtalic anhydride. The composites were maked adding in to graft LLDPE\'s the charge of modified surface silicate micro-spheres whith 3aminepropylsilane or trimethoxyclorinesilane. This work to composites characterization was used thermal and vibrational characterization, and torque, crystalinity degree and mechanical tests. In thermal characterizations were used: termogravimetry (TG) and differential scanning calorimetry (DSC). In the vibrational characterization, the photoacoustic spectroscopy (PAS-IR) and Raman spectroscopy were used. Using the PAS-IR technique it was possible to prove the anhydride bonding in the polyolefin back bones, and also was possible verify the interactions between the functionalized polymer and the charge. With DSC and TG techniques was possible verify changes in composites properties in comparison to originais or functionalized polymers. The mechanical tests show that the functionalized polymer composites have bigger values of elongation and tensile strength in comparison to non functionalized LLDPE composites.
47

Substratinduzierte Differenzierung von Endothelzellen

Herklotz, Manuela 19 August 2008 (has links) (PDF)
Der Erfolg neuer Strategien in der Regenerativen Medizin und im Tissue Engineering hängt maßgeblich von einem gut entwickeltem vaskulären Netzwerk ab, welches die auf den Implantaten wachsenden Zellen und Gewebe versorgen. Oberflächeneigenschaften der Implantate sowie die Präsentation verschiedener Liganden für extrazelluläre Matrixproteine spielen bei der Besiedlung der Implantate, als auch bei der Bildung versorgender Blutgefäße durch die Endothelzellen eine wesentliche Rolle. In dieser Arbeit konnte durch Variation der Anbindungsstärke (kovalent oder physisorptiv) des extrazellulären Matrixproteins Fibronektins an die MSA-Copolymere der Einfluss des Aufbaus der extrazellulären Matrix auf das Differenzierungsverhalten der Endothelzellen gezeigt werden. Auch die initiale Konzentration von Adhäsionsproteinen an der Substratoberfläche zeigte sich bedeutend für das Verhalten der Zellen. Optimal für eine gute Adhäsion, native Entwicklung und Kapillarbildung der Endothelzellen war die stabile (kovalente) Anbindung weniger Adhäsionsproteine (hier Fibronektin) an die Substratoberfläche, so dass die Zellen problemlos adhärieren konnten. Erfolgte die weiter Proteinadsorption an die Oberflächen in einem nativen Zustand (hier auf den hydrophilen Oberflächen) so waren die Endothelzellen in der Lage, die extrazelluläre Matrix zu reorganisieren und ein dem in vivo Zustand ähnlicher Aufbau der extrazellulären Matrix konnte realisiert werden. Dies ermöglichte den Zellen wiederum ein natürliches Verhalten. Die Ausbildung einer moderaten Anzahl von Adhäsionsstellen der Zellen, sowie der in vivo ähnliche Aufbau der Adhäsionspunkte ermöglichte den Zellen einen eher lockeren Kontakt zum Substrat. Daher waren sie sehr flexibel in ihrer Morphologieanpassung. Unter diesen Bedingungen war es möglich, dass die Endothelzellen bei Stimulierung der Angiogenese kapillarähnliche Strukturen ausbildeten. Die Verwendung dreidimensionaler Zellkulturträger zeigte eine Unterstützung der Kapillarbildung der Endothelzellen in Abhängigkeit unter den beschrieben Bedingungen. / The success of tissue engineering strategies using artificial scaffolds crucially depends on a controlled formation of well-developed vascular networks in growing tissues. The presentation of extracellular matrix ligands on scaffolds is often envisioned as an appropriate strategy to support capillary formation. We show that the control of primary coupling mode — covalent versus physisorbed — as well as of secondary interactions of cell-secreted extracellular matrix proteins have a strong impact on endothelial cell development. A set of maleic anhydride copolymer thin films was used as planar model substrates. They exhibit a switchable mode of primary matrix coupling combined with a gradation of secondary matrix–substrate interactions due to a variation of surface hydrophobicity and polarity. We found that the cells adhere in a more native state at a low amount of covalent primary coupled fibronectin ligands in conjunction with weak interactions of secondarily adsorbed adhesion ligands on hydrophilic surfaces. These substrates allow for a formation of capillary-like networks of endothelial cells. High ligand densities and strong secondary hydrophobic interactions inhibit a pronounced capillary formation. The composition and structure of the formed extracellular matrix correlates well with the specific integrin expression pattern. From these results it is concluded that the formation of blood capillaries in artificial scaffolds can be triggered by controlling primary and secondary coupling of cell adhesion ligands to implant materials. 2
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Bioactive coatings to control marine biofouling

Tasso, Mariana Patricia 30 November 2009 (has links) (PDF)
The colonization of immersed surfaces by a myriad of marine organisms is a complex, multi-stage, species-specific process giving rise to economic and environmental costs. This unwanted accumulation of organisms in the marine environment, called biofouling, has been attacked from different fronts, going from the ‘problem-elimination-as-problem-solving’ strategy (essentially through the use of biocides) to more elaborated and environmentally-friendly options based on the principle of ‘non-stick’ or ‘easy foul-release’ surfaces, which do not jeopardize marine life viability. Several marine organisms rely on proteinaceous adhesives to secure a holdfast to surfaces. Proteolytic enzymes have been demonstrated to be effective agents against settlement and settlement consolidation onto surfaces of marine bacteria, algae, and invertebrates, their proposed mode-of-action being the enzymatic degradation of the proteinaceous components of the adhesives. So far, however, the evidence remains inconclusive since most of the published investigations refer to commercial preparations where the enzyme is mixed with other components, like additives, which obviously act as additional experimental variables. This work aims at providing clear, conclusive evidence about the potential of serine proteases to target the adhesives produced by a group of model marine biofoulers. The strategy towards the goal consisted in the preparation and characterization of maleic anhydride copolymer nanocoatings modified by a surface-bound enzyme, Subtilisin A, the active constituent of the commercial preparations reported as effective against biofouling. The enzyme-containing maleic anhydride copolymer films were characterized (enzyme surface concentration, activity, stability, roughness and wettability) and thereafter tested in biological assays with three major biofoulers: spores of the green alga Ulva linza, cells of the pennate diatom Navicula perminuta, and cyprid larvae of the barnacle Balanus amphitrite. The purpose of the biological assays was to elucidate the efficacy of the immobilized catalyst to discourage settlement and/or to facilitate removal of these organisms from the bioactive layers. Results confirmed the initial hypotheses related to the enzymatic degradation of the biological adhesives: the immobilized protease was effective at reducing the adhesion strength of Ulva spores and Navicula diatoms in a manner that correlated with the enzyme activity and surface concentration, and deterred settlement of Balanus amphitrite barnacle cyprids even at the lowest surface activity tested. By facilitating the removal of biofilm-forming diatoms and of spores of the troublesome alga Ulva linza, as well as by interfering with the consolidation of adhesion of the calcareous Balanus amphitrite macrofouler, the enzyme-containing coatings here disclosed are considered to constitute an appealing and promising alternative to control marine biofouling without jeopardizing marine life.
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Sol-gel synthesis of vanadium phosphorous oxides for the partial oxidation of n-butane to maleic anhydride

Salazar, Juan Manuel January 1900 (has links)
Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO[4subscript][dot in middle of line]0.5H[2subscript]O (the precursor) followed by in-situ activation to produce (VO)[2subscript]P[2subscript]O[subscript]7 (the active phase). These catalysts considerably improve their performance when prepared as nanostructured materials and this study discusses an alternative synthesis method based on sol-gel techniques capable of producing nanostructured VPO. Vanadium(V) triisopropoxide oxide was reacted with ortho-phosphoric acid in tetrahydrofuran (THF). This procedure yielded a gel of VOPO[4subscript] with interlayer entrapped molecules. The gels were dried at high pressure in an autoclave with controlled excess and composition of THF-2-propanol mixtures. The surface area of the obtained materials was between 50 and 120 m[2superscript]/g. Alcohol produced by the alkoxide hydrolysis and incorporated along with the excess solvent reduced the vanadium during the drying step. Therefore, after the autoclave drying, the solid VOPO[4subscript] was converted to the precursor; and, non-agglomerated platelets were observed. Use of additional 2-propanol increased the amount of precursor in the powder but reduced its surface area and increased its crystallite size. In general, sol-gel prepared catalysts were significantly more selective than the traditionally prepared materials, and it is suggested that the small crystallite size obtained in the precursor influenced the crystallite size of the active phase increasing their selectivity towards maleic anhydride. The evaluation of these materials as catalysts for the partial oxidation of n-butane at 673 K under mixtures of 1.5% n-butane in air yielded selectivity of 40% at 50% conversion compared to 25% selectivity at similar level of conversion produced by the traditionally prepared catalysts. Variations in the catalytic performance are attributed to observed polymorphism in the activated materials, which is evidenced by remarkable differences in the intrinsic activity. All precursors and catalysts were characterized by IR, XRD, SEM and BET, and the products of the catalytic tests were analyzed by GC.
50

Studies Of Moisture-induced Crosslinking in Some Novel Vinyl Ether-Maleic Anhydride Copolymers and Terpolymers And Synthesis And Characterization Of Hyperbranched Polyketals

Rema, B 03 1900 (has links) (PDF)
No description available.

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