Strengthening silica prepared by sol-gel chemistry by inclusion of a polyamidoamine dendrimer

Silica prepared from tetramethyl orthosilicate by an acid-catalyzed sol-gel process is strengthened by inclusion of a generation-zero polyamidoamine (G0-PAMAM) dendrimer in the precursor sol. Evidence is provided by impact test and rupture strength measurements. Impact mean failure energies are 17 and 30 mJ for undoped and doped silica, respectively. The corresponding rupture strengths are 32.9 and 41.6 MPa. Also measured is the Knoop Hardness Number (KHN) for the undoped and PAMAM-doped silica. The KHN values are indistinguishable among the undoped and doped sol-gels and are within 15% of that reported for borosilicate glass. Doping with generation-4 PAMAM does not strength the gels. A model is proposed whereby the G0-PAMAM crosslinks the silica and G4-PAMAM serves as a templating agent that leads to larger colloidal particles. Atomic force microscopy of the surface features of the silica supports the hypothesis.