Qualitative evaluation of sol–gel SiO2 as a protective layer for soft surfaces

In this paper, it is shown that SiO2 sol–gel coatings deposited on glass and acrylic substrates (polymethyl methacrylate) considerably improved the mechanical resistance of the surface of these materials. We have used new methods to test the mechanical resistance and to measure the damage produced to the surface of the coated and bare substrates. The qualitative method employed to evaluate the mechanical resistance of the bare and coated surfaces consists of exposing the samples to the constant impacts and friction of zirconia balls. For that, the samples were fixed to the inner wall of a ball mill containing the zirconia balls. It is observed that during the mechanical treatment, the bare acrylic substrates lose their transparency, due to a large amount of surface defects created by the mechanical treatment. The presence of the defects is monitored measuring the transmitted light from a laser beam. Long exposure times to the mechanical test show that small amounts of materials are removed from the surface of the coating.