Surface chemical and physical properties of TEOS-TBOT-PDMS hybrid materials

The application of nitrogen adsorption, mercury porosimetry and inverse gas chromatography (IGC) for the examination of surface physical and chemical properties of hybrid materials is discussed. Hybrid materials were prepared from tetraethoxysilane (TEOS), tetrabutyl orthotitanate (TBOT), and hydroxyl terminated polydimethyl siloxane (PDMS) for different TBOT concentrations. It was found that TBOT affects specifie surface areas, pore volumes and pore sizes, but does not affect pore morphology. Surface chemical properties were analyzed by IGC. It was found that the dispersive surface energy was a function of the material pore size. Values between 36 and 42 mJ·m^-2 were obtained for the dispersive surface energy which are consistent with those of hybrid materials. On the other hand, the acid-base (k_A, k _B)urface constants showed good correlation with the TBOT concentration. These materials can be considered as anphoteric ones, and it was found that k_A increases from 1.07 to 1.47, and k_B increases from 0.76 to 1.73 when the TBOT concentration increases from 0 to 7%. Such increase is assigned to the formation of Si-O-Ti bonds as it was deduced from an IR band appearing at 930 cm^-1 in the FT-IR spectra.