Nanoindentation testing of SiO₂-PMMA hybrid films on acrylic substrates with variable coupling agent content

In this work we report the influence of the molar composition of the coupling agent, as well as the curing conditions on the mechanical properties of SiO₂-PMMA (polymethyl methacrylate) hybrid films deposited on organic acrylic substrates. The SiO₂-PMMA hybrid films were deposited by the sol–gel method from hybrid precursor solutions with fixed molar ratio of 1:0.25 for TEOS/MMA (Tetraethyl-orthosilicate/Methylmethacrylate) and TEOS/TMSPM (3-trimethoxysilyl propyl methacrylate) molar ratios ranging from 1:0.05 to 1:0.2. The organic compound TMSPM was used as coupling agent to enhance the bond between the organic and inorganic molecules. The wear resistance, hardness and elastic modulus of the hybrid films were determined by nanoindentation techniques and compared to the substrate mechanical behaviour. The chemical bonding in the hybrid films was analyzed by Fourier Transform Infrared spectroscopy and their transparency by optical transmission and reflection spectroscopy. The friction coefficient and sliding life of the hybrid films were also measured with a pin-on-disc tribometer. The surface morphology and roughness were determined from atomic force microscopy images. The hybrid films with lowest content of coupling agent showed the best mechanical performance in terms of hardness, friction coefficient and wear resistance keeping high optical transparency.