Nanoscale Structures of Sol-Gel Materials

With the development of more sophisticated, mostly multi-precursor sol-gel materials, the structure of the building blocks and their mutual arrangement on a nanoscopic scale is getting more and more important. The question how the structure of oxometallate clusters as primary hydrolysis products is influenced by bidentate organic ligands is discussed for a series of methacrylate-substituted oxozirconium clusters with different metal: methacrylate ratio. On a larger scale, assembly of the molcular building blocks to form a gel network was investigated for gels prepared by base-catalyzed reaction of Si(OR)4/R'Si(OMe)3 mixtures. When the functional organic group R' has no strongly basic properties, the gel network is formed in two stages. The R'Si═ units condense to a gel network formed by the faster reaction of Si(OR)4. When R' contains a strongly basic substituent such as amino groups, both R'Si(OMe)3 and Si(OR)4 are involved in the built-up of the gel network, possibly by extensive hydrogen bonding between the amino groups and silanol groups.