"Sol-gel derived hybrid thin films: the chemistry behind processing". A. A. Letailleur, F. Ribot, C. Boissière, J. Teisseire, E. Barthel, B. Desmazières, N. Chemin, C. Sanchez. CHEMISTRY OF MATERIALS 23, 5082 (2011). DOI: dx.doi.org/10.1021/cm202755g
Despite their apparent simple preparation by sol-gel process, silsesquioxanes
based materials are quite complex and rich systems. Accordingly, a clear
understanding of their elaboration chemistry and its relations to process and properties
are important matter. In the particular case of thin film preparation, vitrification must be
controlled to ensure high throughput and reliability. Using methylsilsesquioxane based
films as a relevant model and a combination of IR spectroscopy, mass spectrometry, and
solution 29Si NMR, a meaningful description of the film structure was obtained.
Furthermore, vitrification, observed by dynamic mechanical analysis, was shown to
depend strongly on the amounts of cages and extended structures present in the films.
More interestingly, the proportion of these species can be tuned through a careful
control of the elaboration chemistry. On one hand, long aging and high dilution yield a
larger amount of cages, which results in a delay of the vitrification. On the other hand,
pH appears as the convenient parameter to finely adjust the time span during which high
quality films can be prepared from the sols, while preserving the film composition and final properties.
based materials are quite complex and rich systems. Accordingly, a clear
understanding of their elaboration chemistry and its relations to process and properties
are important matter. In the particular case of thin film preparation, vitrification must be
controlled to ensure high throughput and reliability. Using methylsilsesquioxane based
films as a relevant model and a combination of IR spectroscopy, mass spectrometry, and
solution 29Si NMR, a meaningful description of the film structure was obtained.
Furthermore, vitrification, observed by dynamic mechanical analysis, was shown to
depend strongly on the amounts of cages and extended structures present in the films.
More interestingly, the proportion of these species can be tuned through a careful
control of the elaboration chemistry. On one hand, long aging and high dilution yield a
larger amount of cages, which results in a delay of the vitrification. On the other hand,
pH appears as the convenient parameter to finely adjust the time span during which high
quality films can be prepared from the sols, while preserving the film composition and final properties.
A pesar de lo sencillo de su preparación mediante el proceso sol-gel, los materiales basados en silsesquioxanos son sistemas sumamente ricos y complejos. En consecuencia, es importante entender claramente su química de elaboración y sus relaciones con el proceso y con sus propiedades. En el caso particular de la preparación de películas delgadas, la vitrificación debe ser controlada para asegurar una alta calidad y reproducibilidad. Utilizando como modelo relevante a las películas hechas de metilsilsesquioxano, además de una combinación de espectroscopias IR, de masa y 29SiNMR, se obtiene una descripción, con sentido, de la estructura de la película. Es más, se muestra que la vitrificación, observada por medio de análisis mecánicos dinámicos, depende fuertemente de las cantidades de celdas y de estructuras extendidas dentro de las películas. Más interesante aún, la proporción existente entre estas especies puede ser modificada a través de un control cuidadoso de la química de elaboración. Por un lado, un envejecimiento largo y una alta disolución inducen una mayor cantidad de celdas, lo cual resulta en un retraso en la vitrificación. Por otro lado, el pH resulta ser un parámetro conveniente para ajustar finamente el intervalo de tiempo durante el cual se pueden preparar películas de alta calidad a partir de los soles, siempre preservando la composición de la película y sus propiedades finales.
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