Surface changes during pyrolytic conversion of hybrid materials to oxycarbide glasses

Hybrid materials from TEOS-TBOT-PDMS have been prepared and pyrolyzed between 400 and 1,000 °C. The surface characteristics of this type of materials have been studied by nitrogen adsorption, mercury intrusion porosimetry, and inverse gas chromatography at infinite dilution (IGC). IGC has been used for obtaining the dispersive and acid-base surface energies of the different materials. The specific surface areas and pore volumes of the studied samples have resulted to increase the pyrolysis temperatures ranging between 400 and 600 °C and decrease for higher temperatures. On the other hand, surface energies increase when the materials are pyrolyzed between 400 and 800 °C and then decrease after pyrolysis at 1,000 °C. When the material is pyrolyzed at the highest temperature, the surface energies are close to that of typical glasses. It has been observed that pyrolyzing at 800 °C the material has the highest values of both components of the surface free energy (dispersive and specific). The surface energy-pyrolysis temperature variation does not correspond to the formation of micropores in the material during the pyrolysis process. Therefore, it has been assumed that high energy active sites must be formed on the surface when the materials are pyrolyzed at 800 °C.