Propriedades ópticas em filmes de opalas sintéticas
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Data
2007-02-02
Autores
Papacídero, Andréa Taveira [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho foi estudado um sistema para preparação de materiais com estrutura tridimensional organizada: esferas monodispersas de sílica e seu empacotamento. A preparação de esferas monodispersas baseou-se na modificação de metodologias de síntese já existentes na literatura a fim de se obter um maior controle no tamanho final e na distribuição de diâmetro das esferas. Esferas monodispersas de sílica (350<j<520 nm) foram produzidas através de uma adaptação à metodologia de Stober. As esferas de sílica preparadas, foram ordenadas na forma de filmes em substratos de vidro, a partir da adaptação de um método de cristalização coloidal baseado na evaporação do solvente. Neste método, substratos de vidro são inicialmente inseridos verticalmente no centro de um vial contendo uma dispersão coloidal de esferas de sílica (2,5 v/v em etanol). Este vial é mantido sob temperatura constante de 70° C l 0,05, de modo que as esferas sejam depositadas, com a evaporação do solvente, de maneira organizada na região do menisco. Através deste procedimento, as amostras preparadas apresentam um elevado grau de organização quando comparada aos resultados da literatura. Esta qualidade das amostras foi verificada pelo aspecto iridiscente bem como pelos espectros de reflectância especular com ângulo variável e Microscopia Eletrônica de Varredura. As esferas de sílica também foram dopadas com o íon Eu3+ hidratado e com o composto [Eu(tta)3(H2O)2] onde tta é o ligante tenoiltrifluorobetadicetona. O estudo espectroscópico levou a caracterização do processo de adsorção destas espécies sobre as esferas. A emissão de banda larga característica de defeitos na superfície das esferas também foi estudada em função da temperatura. A supressão desta emissão ocorre para tratamentos térmicos a temperatura acima de 600oC.
In the present work the preparation of monodisperse silica spheres and the colloidal crystalization leading to a three-dimensional structure were explored. Monodisperse spheres were prepared based in methodologies adapted from the literature in order to get a better control in the final size and diameter distribution of the spheres. Monodisperse silica spheres (350<j<520 nm) were produced using a modified Stober method. The colloidal crystal films of silica spheres were obtained by a controlled- solvent evaporation method. In this method, a glass substrate was vertically centered in a vial, the temperature was kept at 70° C l 0,0,5 and the silica particles were forced into an ordered arrangement on the surface of a vertical glass substrates, because the meniscus was swept downwards by evaporation of the solvent. Through this procedure, the samples obtained showed a good 3D arrangement when compared with results from literature. This quality of the sample was confirmed by the iridescent aspect, variable angle specular reflectance and Scanning Electron Microscopy. Silica spheres were doped with hydrated Eu3+ ions and also with the compound [Eu(tta)3(H2O)2] where tta stands for the thenoyltrifluorobetadiketone ligand. The adsorption processes could be probed by spectroscopic measurements. The characteristic broad emission band of amorphous silica was also studied as a function of the temperature. A complete quenching was observed for heat treatments above 600°C.
In the present work the preparation of monodisperse silica spheres and the colloidal crystalization leading to a three-dimensional structure were explored. Monodisperse spheres were prepared based in methodologies adapted from the literature in order to get a better control in the final size and diameter distribution of the spheres. Monodisperse silica spheres (350<j<520 nm) were produced using a modified Stober method. The colloidal crystal films of silica spheres were obtained by a controlled- solvent evaporation method. In this method, a glass substrate was vertically centered in a vial, the temperature was kept at 70° C l 0,0,5 and the silica particles were forced into an ordered arrangement on the surface of a vertical glass substrates, because the meniscus was swept downwards by evaporation of the solvent. Through this procedure, the samples obtained showed a good 3D arrangement when compared with results from literature. This quality of the sample was confirmed by the iridescent aspect, variable angle specular reflectance and Scanning Electron Microscopy. Silica spheres were doped with hydrated Eu3+ ions and also with the compound [Eu(tta)3(H2O)2] where tta stands for the thenoyltrifluorobetadiketone ligand. The adsorption processes could be probed by spectroscopic measurements. The characteristic broad emission band of amorphous silica was also studied as a function of the temperature. A complete quenching was observed for heat treatments above 600°C.
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Cristais (Química) -, Europio
Como citar
PAPACÍDERO, Andréa Taveira. Propriedades ópticas em filmes de opalas sintéticas. 2007. 59 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Química, 2007.