Hybrid sol-gel coatings produced from TEOS and γ-MPS

Hybrids sols from tetraetoxysilane (TEOS) and 3-(methacryloxypropyl) trimethoxysilane (gamma-MPS) were prepared in acid medium for different TEOS/gamma-MPS ratios and were modified by the addition of a colloidal silica suspension. The stability of the different sols was evaluated by viscosity measurements; the sols showed a Newtonian behaviour and the ageing effect was negligible even after two months from their preparation. Coatings were obtained by dipping at different withdrawal rates and heat-treated between 150 and 250degreesC. Transparent coatings with thickness higher than 4 mum were reached for most of the studied compositions. The surface microhardness of coatings for each composition and thermal treatment was evaluated by the pencil hardness test. The thermal stability was followed by simultaneous thermogravimetric and differential thermal analysis (TGA-DTA) determining the limit temperatures at which the coatings can be treated without losing its hybrid character. A structural analysis was made by deconvolution of Fourier transformed infrared spectra (FTIR) of self-supported films observing the influence of the organic groups on the silica network.