Surfactant removal and silica condensation during the photochemical calcination of thin film silica mesophases.
J Phys Chem B
; 109(30): 14551-6, 2005 Aug 04.
Article
em En
| MEDLINE
| ID: mdl-16852834
ABSTRACT
The evolution of photochemical surfactant removal and silica condensation from organically templated thin film silica nanocomposites with mesoscopic ordering has been probed using a combined application of Fourier transform infrared (FT-IR) spectroscopy and single wavelength ellipsometry. Thin films of silica nanocomposites were prepared by a previously reported evaporation-induced self-assembly process. Specifically, oxidized silicon and gold substrates were withdrawn at 25 mm/min from a subcritical micelle concentration solution containing an ethylene oxide surfactant as a structure-directing agent and tetraethyl orthosilicate as a silica precursor. Real-time grazing incidence difference FT-IR spectra of the nanocomposite films on gold taken during exposure to short-wavelength ultraviolet light (184-257 nm) show that surfactant removal and silica condensation occur gradually and concomitantly. Surfactant removal and silica reconstructions were found to be nearly complete after 90 min of exposure. Further, a transient feature was observed in the FT-IR spectra around 1713 cm(-1) during the UV exposure process and was assigned to a carbonyl (C=O) stretching mode absorption, reflecting the transient formation of a partially oxidized surfactant intermediate. From these data we propose a stepwise model for surfactant removal from the nanocomposite films. Ellipsometrically determined index of refraction values collected as a function of UV exposure are also shown to support such a stepwise mechanism of surfactant removal from the ordered nanocomposite silica thin film mesophases studied here.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Tensoativos
/
Dióxido de Silício
Idioma:
En
Ano de publicação:
2005
Tipo de documento:
Article