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Structural Evolution During the Sol to Gel Transition of Silicon-Alkoxide Based Sols Observed by Cryogenic Transmission Electron Microscopy (CRYO-TEM)

  • Joseph K. Bailey (a1) and Martha L. Mecartney (a1)

Abstract

The gelation reaction for tetraethoxysilane in both acid and base catalyzed environments was studied using cryogenic transmission electron microscopy. The evolution of the gel structure was observed in wet samples by the technique of fast-freeze vitrification, in which the three dimensional gel structure is preserved in vitreous solvent. The sample is then observed in the electron microscope using a cold stage. Samples were prepared and allowed to react until a specific point of gelation was reached, then were vitrified at that point. Results from this technique show a coarse network structure for base catalyzed gels. This network is composed of silica clusters ≈40Å in size. The acid catalyzed gels show an extremely fine texture (<10Å) at end point of gelation. The structures at intermediate stages of gelation were also determined.

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