Solid freeform fabrication of organic-inorganic hybrid materials

Freeform fabrication methods build materials by the repetitive addition of thin layers. In principle, these methods are very applicable to sol-gel glasses and organic-inorganic hybrids where diffusion and shrinkage during solidification are important. The chemical conversion of metal alkoxides to oxides may require the diffusion of water into the part and does require the diffusion out of the alcohol reaction products. If this conversion can occur in the layers as they form, the diffusion paths are short and so the reaction rate should be much higher. The conversion of alkoxide to oxide also involves a large reduction in volume, which can be accommodated in elastomers but leads to distortion and cracking of thick, rigid parts. Again, conversion layer by layer may eliminate these effects. Here we describe the use of extrusion freeform fabrication to make bars of mineralized gel, of silicate glass and of methacrylate-silica hybrids. Glass parts can only be made if the shrinkage on hydrolysis is minimized by including a large fraction of glass powder. For the hybrids, solid bars crack during the hydrolysis of the alkoxide but open mesh structures can be formed without cracking. Both solid and mesh bars of mineralized gel can be formed. The mesh structures give good mechanical properties in each case, with up to 50 vol.% inorganic phase and bend strengths in the range from 50–100 MPa.