Síntese e Caracterização de Materiais Nanohíbridos Orgânicos/Inorgânicos Multifuncionais Obtidos pelo Processo Sol-gel
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2008
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O trabalho de doutoramento envolveu a síntese e caracterização de sistemas híbridos orgânico-inorgânicos de classe II inovadores, pelo processo sol-gel convencional a baixa temperatura, e em condições ácidas hidrolíticas e a temperaturas elevadas. Os materiais híbridos analisados foram englobados em três sub-classes. Na primeira sub-classe encontra-se a rede híbrida di-ureasils, a qual é composta por cadeias de polioxietileno de diferentes comprimentos ligadas covalentemente a uma rede siliciosa através de grupos ureia. Os materiais híbridos di-amidosils e mono-amidosils constituem outra sub-classe, sendo baseados numa rede siliciosa e em cadeias de polietileno de diferentes comprimentos, sendo a ligação entre os dois componentes através de nós de ligação de tipo amida. Por último, investigou-se a
rede híbrida di-poli(ε-caprolactona)(530)/siloxano, baseado numa rede siliciosa e em cadeias de poli(ε-caprolactona), sendo a ligação entre os componentes inorgânico e orgânico efectuada através de nós de ligação de tipo uretano.
Foi possível observar que os materiais di-ureasils dopados apresentam condutividades moderadas a elevadas. O comportamento mais interessante de referir foi detectado no sistema di-ureasil d-U(2000)nKCF3SO3. Este material foi testado com sucesso num dispositivo electrocrómico, apresentando uma boa estabilidade electroquímica e efeito memória, sendo deste modo um candidato promissor para aplicação em “janelas inteligentes”. Para os presentes materiais híbridos dopados foi realizada uma análise espectroscópica profunda com o objectivo de determinar as espécies iónicas responsáveis pelo máximo de condutividade iónica, tendo-se concluído que aniões “livres” e iões fracamente coordenados são os principais responsáveis pela condução. Esta análise permitiu também descrever em detalhe as interacções catião/polímero e catião/ureia. Relativamente aos materiais híbridos amidosils, constatou-se que o comprimento das cadeias metilénicas e as condições experimentais de síntese utilizadas representam factores importantes na organização estrutural dos híbridos. O material híbrido mono-amidosil m-A(14) apresenta uma supraestrutura lamelar bicamada de elevada organização, cuja luminescência exibe um efeito memória termicamente activado, além de apresentar uma natureza nanoscópica totalmente invulgar. Foi possível constatar a possibilidade de funcionalizar esta e de híbrida através da dopagem com catiões, observando-se que a presença de iões K+, Mg2+ e Eu3+ conduz, para além da formação da fase cristalina lamelar formada no m-A(14), ao crescimento de uma nova fase cristalina, também lamelar, de maior grau de ordem e com menor distância interlamelar que esta. Concluiu-se igualmente que, através de alteração das condições experimentais do processo sol-gel, foi possível transformar um material amorfo (m-A(8)) num material hierarquicamente organizado, tal como o híbrido m-A(14). A síntese do sistema híbrido di-poli(ε-caprolactona)(530)/siloxano permitiu desenvolver um material biodegradável com potencial para as áreas de electroquímica do estado sólido.
The present work involved the characterization of innovative class II organic-inorganic hybrid systems, synthesized by the conventional sol-gel process at low temperature, in hydrolytic acid conditions and high temperatures. The hybrid materials investigated belong to three sub-classes. The first sub-class includes the di-ureasils, which are composed of poly(oxyethylene) chains with variable length bonded covalently to a siliceous framework by means of urea cross-links. The di-amidosil and mono-amidosil hybrids which represent another sub-class, are composed of a siliceous framework and polyethylene chains with different length bonded by means of amide cross-links. The last sub-class of hybrids investigated was the dpoly( ε-caprolactone)(530)/siloxano hybrid, based on a siliceous framework and poly(ε-caprolactone) (PCL) chains linked by means of urethane cross-links. The doped-di-ureasils hybrids exhibit moderate to high levels of ionic conductivity. The most interesting behaviour worth referring was detected in the d-U(2000)nKCF3SO3 di-ureasil hybrid. This material was tested with success as electrolyte in an electrochromic device, which exhibits good electrochemical stability, memory effect and may therefore be of interest for application in “smart windows”. For these doped-di-ureasils hybrid materials a FT-IR and FT-Raman spectroscopic study was carried out with the aim of determining the main charge carriers of the sample that corresponds to conductivity maximum. Through this analysis we concluded that “free” anions and weakly coordinated anions, detected in all the samples examined, were the main species responsible for the ionic conductivity. This analysis also allowed us to analysed indepth the following interactions: cation/polymer and cation/urea. In the case of the amidosil hybrid materials, we conclude that the length of the methylene chains and the experimental conditions used in the synthetic procedure represent important factors in the structural organization of the hybrids. The highly organized bilayer mono-amidosil hybrid m-A(14) suprastructure exhibits a thermally-actuated photoluminescence memory effect and presents unique nanoscopic photoluminescence sensitivity. It was possible to functionalize this hybrid network through the incorporation of cations. The presence of K+, Mg2+ and Eu3+ ions in the m-A(14) hybrid material induced the growth of a new crystalline phase, also lamellar, of larger order degree and with smaller interlamelar distance than that of the m-A(14) monoamidosil. Another conclusion worth reporting is the possibility of transforming an amorphous material (m-A(8)) in to a hierarchically-structured organized bilayer as in the case of the hybrid m-A(14), through the alterations of the experimental conditions. The synthesis of the d-poly(ε-caprolactone)(530)/siloxane hybrid material allowed us to develop a biodegradable material with foreseen applications in the domain of solid-state electrochemistry.
The present work involved the characterization of innovative class II organic-inorganic hybrid systems, synthesized by the conventional sol-gel process at low temperature, in hydrolytic acid conditions and high temperatures. The hybrid materials investigated belong to three sub-classes. The first sub-class includes the di-ureasils, which are composed of poly(oxyethylene) chains with variable length bonded covalently to a siliceous framework by means of urea cross-links. The di-amidosil and mono-amidosil hybrids which represent another sub-class, are composed of a siliceous framework and polyethylene chains with different length bonded by means of amide cross-links. The last sub-class of hybrids investigated was the dpoly( ε-caprolactone)(530)/siloxano hybrid, based on a siliceous framework and poly(ε-caprolactone) (PCL) chains linked by means of urethane cross-links. The doped-di-ureasils hybrids exhibit moderate to high levels of ionic conductivity. The most interesting behaviour worth referring was detected in the d-U(2000)nKCF3SO3 di-ureasil hybrid. This material was tested with success as electrolyte in an electrochromic device, which exhibits good electrochemical stability, memory effect and may therefore be of interest for application in “smart windows”. For these doped-di-ureasils hybrid materials a FT-IR and FT-Raman spectroscopic study was carried out with the aim of determining the main charge carriers of the sample that corresponds to conductivity maximum. Through this analysis we concluded that “free” anions and weakly coordinated anions, detected in all the samples examined, were the main species responsible for the ionic conductivity. This analysis also allowed us to analysed indepth the following interactions: cation/polymer and cation/urea. In the case of the amidosil hybrid materials, we conclude that the length of the methylene chains and the experimental conditions used in the synthetic procedure represent important factors in the structural organization of the hybrids. The highly organized bilayer mono-amidosil hybrid m-A(14) suprastructure exhibits a thermally-actuated photoluminescence memory effect and presents unique nanoscopic photoluminescence sensitivity. It was possible to functionalize this hybrid network through the incorporation of cations. The presence of K+, Mg2+ and Eu3+ ions in the m-A(14) hybrid material induced the growth of a new crystalline phase, also lamellar, of larger order degree and with smaller interlamelar distance than that of the m-A(14) monoamidosil. Another conclusion worth reporting is the possibility of transforming an amorphous material (m-A(8)) in to a hierarchically-structured organized bilayer as in the case of the hybrid m-A(14), through the alterations of the experimental conditions. The synthesis of the d-poly(ε-caprolactone)(530)/siloxane hybrid material allowed us to develop a biodegradable material with foreseen applications in the domain of solid-state electrochemistry.
Descrição
Tese de Doutoramento em Ciências e Engenharia de Materiais
Palavras-chave
Química orgânica , Engenharia dos materiais , Materiais nanoestruturados