Multi-nuclear liquid state NMR investigation of the effects of pH and addition of polyethyleneglycol on the long-term hydrolysis and condensation of tetraethoxysilane

The long-time behavior of the hydrolysis and condensation reaction of the tetraethoxysilane (TEOS) pre-solution at different pH values with and without addition of polyethyleneglycol (PEG) for various aging times was characterized by liquid 1H, 13C, and 29Si NMR spectroscopy. After aging, the alcohol is released in the TEOS pre-solution without addition of PEG at pH 3 and 9. On the other hand, the hydrolysis and condensation rates of the TEOS pre-solutions with addition of PEG at pH 3 and 9 increase except for the TEOS pre-solution with addition of PEG 2000 at pH 9. However, the hydrolysis and condensation rates of the TEOS pre-solutions with and without addition of PEG at pH 5 and 7 are almost the same before and after aging. The effects of the pH values, polymer size and aging times on the hydrolysis and condensation reaction of the TEOS pre-solutions are discussed.

The long-time behavior (tens and hundreds hours after initiation) of hydrolysis and condensation of TEOS as well as the effects of pH and presence of polymers can be characterized with multi-nuclear NMR spectroscopy. Shown here are the relative concentrations of TEOS for the TEOS pre-solution (a) with and without adding PEG at pH 3, (b) with and without adding PEG at pH 9.Figure optionsDownload high-quality image (70 K)Download as PowerPoint slideResearch highlights
► The long time behavior of sol-gel process of TEOS is investigated with multi-nuclear liquid state NMR spectroscopy.
► After aging, the alcohol is released in the TEOS pre-solution without addition of PEG at pH 3 and 9.
► The hydrolysis and condensation rates of the TEOS pre-solutions are found to depend on pH and the size of polymer molecules added.
► The effects of the pH values, polymer size and aging times on the hydrolysis and condensation reaction of the TEOS pre-solutions are explained.