Nanoindentation and adhesion of sol-gel-derived hard coatings on polyester

We investigated sol-gel-derived silica-based hard coatings on modified poly ester substrates. The silica network was modified by incorporating an organ ic component and adding transition metal oxides. These modifications result ed in tailored thermal, optical, and mechanical properties of the coatings. Various low-temperature densification techniques were studied including so l-preparation procedure, enhanced solvent evaporation, ultraviolet irradiat ion, and low-temperature heating (below 150 degrees C). Oxygen plasma etchi ng was applied to improve the adhesion of the sol-gel coatings on the plast ic surface. Nanoindentation analysis revealed that the coatings have a surf ace hardness up to 2.5 +/- 0.27 GPa and an elastic modulus up to 13.6 +/- 0 .4 GPa, approximately an order of magnitude higher than that of the plastic surface.