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 te st and rupture strength measurements. Impact mean failure energies are 17 a nd 30 mJ for undoped and doped silica, respectively. The corresponding rupt ure strengths are 32.9 and 41.6 MPa. Also measured is the Knoop Hardness Nu mber (KHN) for the undoped and PAMAM-doped silica. The KHN values are indis tinguishable among the undoped and doped sol-gels and are within 15% of tha t 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 collo idal particles. Atomic force microscopy of the surface features of the sili ca supports the hypothesis.