Mechanical properties of hybrid sol-gel derived films as a function of composition and thermal treatment

Sol-gel coatings derived from glycidoxypropyltrimethoxysilane (GLYMO) and/or methyltrimethoxysilane (MTMS) and silica nanoparticle filler were prepared. The mechanical properties of the coatings were measured as a function of coating composition and thermal treatment temperature using nanoindentation. Thermogravimetric analysis was used to determine the material loss rate during heating and the thermal stability of the materials. The coating hardness (H) and reduced modulus (Er) strongly increased with increasing thermal treatment temperatures. The changes in the mechanical properties were found to correlate with the conversion of silanol groups measured by infrared spectroscopy. The partial replacement of MTMS by GLYMO in the coatings initially increased the hardness and modulus but larger proportions of GLYMO reduced H and Er. It was found that both thermal treatment temperature and variation in coating composition could result in large changes in the key material ratio of H3/Er2, that in turn could strongly influence the mechanical response of the coating.