Skip to main content Accessibility help
×
Home

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

  • Kenneth G. Sharp (a1)

Abstract

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.

Copyright

References

Hide All
1. Rabinovich, E. M., Wood, D. L., Materials Research Soc. Better Ceramics through Chemistry II 73, 251 (1986).
2. Schmidt, H., J. Non Cryst. Solids 73, 681–91 (1985).
3. Schmidt, H., Scholze, H., Kaiser, A., J. Non-Cryst. Solids 63, 111 (1984).
4. Delattre, L., Babonneau, F., Mater. Res. Soc. Symp. Proc. 346, 365–70 (1994).
5. Perfluoro alcohols such as CF3OH are unstable, decomposing into HF and a perfluoroaldehyde or -ketone; the perfluoroalkyl groups must be separated from the oxygen by at least one methylene group.
6. Hrubesh, L. W., Tillotson, T. M., Poco, J. F., Mater. Res. Soc. Symp. Proc. 180, 315–19 (1990).
7. Tillotson, T. M., Hrubesh, L. W., J. Non-Cryst. Solids 145, 4450 (1992).
8. Woignier, T., Phalippou, J., J. Non-Cryst. Solids 93, 1721 (1987).
9. Scherer, G. W., J. Non-Cryst. Solids 142, 1835 (1992).
10. Scherer, G. W., Faraday Discuss. 101, 225234 (1995).
11. Brinker, C. J., Scherer, G. W. Sol-gel Science; Academic Press: San Diego, CA, 1990.
12. Brinker, C. J., J. Non-Cryst. Solids 100, 3150 (1988).
13. Colby, M. W., Osaka, A., Mackenzie, J. D., J. Non-Cryst. Solids 99, 129–39 (1988).
14. Gottardi, V., Guglielmi, M., Bertoluzza, A., Fagnano, C., Morelli, M. A., J. NonCryst. Solids 63, 7180 (1984).
15. Eaborn, C. Organosilicon Compounds; Butterworth Scientific: London, 1960.
16. Scherer, G. W., J. Non-Cryst. Solids 108, 1827 (1989).
17. Jones, W. M., Fischbach, D. B., J. Non-cryst. Solids 101, 123 (1988).
18. Acker, E. G., J. Colloid Interface Sci. 32, 4154 (1970).
19. Kozuka, H., Sakka, S., Chem. Mater. 1, 398404 (1989).
20. Coltrain, B. K., Melpolder, S. M., Salva, J. M.. “Effect of hydrogen ion concentration on gelation of tetrafunctional silicate sol-gel systems”; Ultrastruct. Process. Adv. Mater., 1992, Int. Conf. Ultrastruct. Process. Ceram., Glasses Compos.
21. Woignier, T., Phalippou, J., Vacher, R., Mater. Res. Soc. Symp. Proc. 121, 697702 (1988).
22. Fricke, J., Gross, J., Mater. Eng. (N. Y.) 8, 311–36 (1994).
23. Kelts, L. W., Armstrong, N. J., Mater. Res. Soc. Symp. Proc. 121, 519–22 (1988).
24. Silanol-bearing species might not, however, elute from the gas chromatograph.
25. Teflon (polytetrafluoroethylene) itself is virtually insoluble due to its extremely high molecular weight and crystallinity.
26. Sharp, K. G., J. Sol-Gel Sci. Technol. 2, 3541 (1994).
27. Michalczyk, M. J., Sharp, K. G. and Stewart, C. W., U.S. Patent 5,726,247, issued to the DuPont Co.
28. Haskell Laboratories, DuPont Co.

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed