Preparation of organic/inorganic hybrid silica using methyltriethoxysilane and tetraethoxysilane as co-precursors

The preparation of a clear, organic/inorganic hybrid silica sol using methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) as co-precursors under alkaline conditions is reported. Two types of alkaline catalysts-ammonia and tetra-methyl-ammonium hydroxide (TMAH)-were examined for use in the preparation of colloidal sols of < 100 nm in diameter, which are suitable for fabrication of nanoporous hydrophobic membranes. Factors that might influence sol preparation were investigated. When ammonia was used as the catalyst, the hydrolysis-polymerization reaction ratio decreased with both an increase in the molar ratio of MTES/TEOS, and a reduction in the water molar ratio. However, when TMAH was used as the catalyst, the water molar ratio had no effect on the hybrid sol preparation reactions. Even systems that employed higher molar ratios of MTES/TEOS or a lower water molar ratio relative to those of the original reactants, allowed for successful preparation of clear sols with a mean sol particle size of < 40 nm.