Falcaro, Paolo and Grosso, David and Amenitsch, Heinz and Innocenzi, Plinio (2004) Silica orthorhombic mesostructured films with low refractive index and high thermal stability. The Journal of Physical Chemistry. B, Vol. 108 (30), p. 10942-10948. eISSN 1520-5207. Article.
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Silica mesoporous films have been synthesized via Evaporation Induced Self-Assembling (EISA) using Pluronic F-127 as a templating agent and mesostructures with Fmmm orthorhombic symmetry have been obtained. An optimized thermal process to stabilize the silica walls has been used; the silica films exhibited an excellent thermal stability in a large range of temperatures and the mesostructure remained organized up to 950 °C. Fourier transform infrared spectroscopy has shown that the high thermal stability is correlated with a progressive strengthening of the silica structure during thermally-induced polycondensation reactions and structural rearrangements of 4-fold rings present in the silica walls. The mesostructure after annealing at 850 °C is free of silanols and still maintains a high degree of order. The refractive index, volume porosity, and shrinkage have been studied as a function of the thermal treatment up to 1050 °C. The films have a low refractive index (1.32), upon removal of the organic template via thermal calcination, and show a 30% residual porosity up to 850 °C.
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