Hard UV-curable organo-mineral coatings for optical applications

Organically-modified silicate incorporating various amounts of zirconium precursor was synthesized via a sol–gel route. The material was deposited as thin films on PMMA substrates and densified by UV-curing. Mechanical properties were measured by nanoindentation and data were recorded continuously as a function of the penetration depth during the loading–unloading cycles. Values of hardness and Young modulus were found in the range 340–440 MPa and 4–6 GPa, respectively. It was shown that these values could be tailored by varying the relative amount of zirconium in the layer. The material exhibited a very elastic behaviour that was related to its high degree of cross-linking assessed by infrared spectroscopy. Results were compared with measurements published by various groups on related materials. The mechanical and optical properties of the samples made this class of materials promising as hard coatings for optical applications.