A new type of sol-gel-based transparent inorganic-organic nano composites
has been developed by increasing the inorganic phase dimension to values
just below the point, where scattering can be neglected. For this purpose,
nanosized boehmite particles ≤ 50 nm are homogeneously incorporated in a sol
based on tetraethoxysilane and an epoxysilane. The nano-scale boehmite
particles act as catalysts for the polymerization of the epoxy silane to
polyethylene oxide, as proved by 13C NMR, and are linked to the
matrix by Si-O-Al bridges, as proven by 27Al-NMR spectroscopy.
The synthesized sols can be applied by standard coating techniques on
transparent polymers and are cured thermally. The mechanical properties
(scratch resistance, hardness) have been substantially improved compared to
systems with molecular dimensions of the inorganic phase. The effect is
attributed to the special structure of flexibly suspended nano-scale
boehmite particles in an inorganic-organic network by a tailored
interface.