A New Type of a Sol-Gel-Derived Inorganic-Organic Nanocomposite

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Abstract
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.