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Schnell Gel: Rapid Formation of Low Density Gels from a Tetra(Fluoroalkoxy)Silane

  • Kenneth G. Sharp (a1)


A new family of simple precursors to silica gel has been developed. The gel precursors are tetra(polyfluoroalkoxy)silanes, the prototype being Si(OCH2CF3)4. Formation of transparent monolithic gels with no added catalyst can be six orders of magnitude faster than comparable reactions of Si(OCH2CH3)4[TEOS]. Extremely low density gels can be generated in minutes at concentrations at which TEOS does not gel at all. Pore sizes in the wet gels were estimated from hydrodynamic relaxation in a beam-bending experiment on cylindrical logs. In a gel at 1% solids, the pore size was approximately 100 nm. Monolithic gels can be created at concentrations at least as low as 0.1% solids and have higher moduli than predicted. NMR and GC/IR evidence indicates extremely facile hydrolysis and condensation pathways and very few silanol or cyclic intermediates in the sol. The chemistry can also be conducted in perfluorinated solvents, enabling synthesis of silica/fluoropolymer nanocomposites.



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