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

The structural perturbations induced by polytetrahydrofuran (PTHF) on sol-g el hybrid films were identified by Fourier-transform infrared (FTIR) spectr oscopy. The films were prepared by spin-coating, from aged solutions contai ning tetraethylorthosilicate (TEOS) as the inorganic precursor and differen t 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 vib ration of 4-fold siloxane rings, whose intensity grows as the polymer conte nt 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 longitudin al (LO) and transverse optical (TO) modes of that vibration in 4-fold silox ane 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 th e band at similar to 950 cm(-1)) increase. These conjugated observations le ad to the conclusion that the polymer hinders the condensation reactions, b eing responsible for a more porous structure, with retention of a larger pr oportion of 4-fold siloxane rings. For high concentrations of high molecula r weight PTHF, the defect structure of the films indicates that a partial s egregation of the polymer occurs. (C) 2001 Elsevier Science B.V. All rights reserved.