The defect structure of sol-gel-derived silica/polytetrahydrofuran hybrid films by FTIR

The structural perturbations induced by polytetrahydrofuran (PTHF) on sol-gel hybrid films were identified by Fourier-transform infrared (FTIR) spectroscopy. The films were prepared by spin-coating, from aged solutions containing tetraethylorthosilicate (TEOS) as the inorganic precursor and different concentrations of PTHF. All the spectra reveal a set of bands that may be associated with structural defects of the silica network. The hybrid films show an additional 'defect' band at 560 cm(-1), assigned to a skeletal vibration of 4-fold siloxane rings, whose intensity grows as the polymer content or molecular weight increases. The relative intensity of two components of the v(as)Si-O-Si mode (resolved by deconvolution of the band at similar to 1080 cm(-1)) grow accordingly. They were thus assigned to the longitudinal (LO) and transverse optical (TO) modes of that vibration in 4-fold siloxane rings. Simultaneously, the bands assigned to the vSi-O- mode and to the vSi-O(H) mode of unreacted silanol groups (obtained by deconvolution of the band at similar to 950 cm(-1)) increase. These conjugated observations lead to the conclusion that the polymer hinders the condensation reactions, being responsible for a more porous structure, with retention of a larger proportion of 4-fold siloxane rings. For high concentrations of high molecular weight PTHF, the defect structure of the films indicates that a partial segregation of the polymer occurs. (C) 2001 Elsevier Science B.V. All rights reserved.