Microstructure and optical properties of PMMA/gel silica glass composites

Abstract

FT-Raman and near infrared (NIR) spectroscopies have been used to investigate PMMA/gel silica composites prepared by the post-doping method. The changes of the vibrational features of silanols on the silica surface and ester carbonyls from PMMA indicate that the two phases in the organic-inorganic hybrids interact with each other through hydrogen-bonding. Unlike unmodified gel silica, the as-prepared composites are hydrophobic due to the elimination of the accessible adsorbing sites provided by the surface silanols. Residual water inherited from the preparation process is not evenly distributed in the composites but locally enriched on the silica surface by hydrogen-bonding to limited surface silanols. The conversion efficiency of MMA-to-PMMA depends not only on the polymerisation conditions applied, but also on the initial structure of the sol-gel substrate used. The composites show high optical transmittance in the near UV and visible region due to a reduction of scattering from an originally porous structure. However, their application in the near IR is restricted due to the combined vibrational energy absorptions by different silanol and water species, and in particular by C-H functional groups from organic modifiers.