Spectroscopic studies of sol-gel-derived organically modified silicates

FT-Raman, near infrared (NIR) and YV-visible spectroscopies have been used to investigate organically modified silicates (ormosils) prepared by the sol-gel process. The materials were characterised in relation to their chemical structures, optical properties and molecular interactions between organic components and inorganic matrices. The organic components of ormosils heavily influence the formation of the inorganic network structure. In general, the incorporation of non-reactive organic groups in the inorganic network creates more interrupted or open structures in comparison with the corresponding non-modified system. The interactions between organic and inorganic components are throughout the entire sol-gel matrix which can be both intermolecular and intramolecular. This distinguishes the ormosils from the other type of organic/inorganic sol-gel composite prepared by the in situ polymerisation method in which such interactions are confined to the boundary between the organic and inorganic phases. These materials are hydrophobic to various extents due partially to the presence of hydrophobic organic groups on the surface and partially to the reduction of the accessible pore surface where adsorption of atmospheric water predominantly occurs. In general, organically modified optical composites are best used in the near UV and visible region, and their application in the near IR is restricted to some extent due to the overtone and combination vibrational energy absorptions by both the organic and inorganic species present in the materials.