Effect of filler size and surface condition of nano-sized silica particles in polysiloxane coatings

Silica nanoparticles with different sizes (from 14 to 60 nm) and different surface modifications (hydrophobic treatment, core–shell structures) are synthesized as colloids and introduced at different concentrations in polysiloxane type coatings in order to perform indentation and scratch experiments. The adding of fillers increases the Young's modulus of the coatings but decreases the 200-μm scratch resistance. The weakness of matrix–filler interactions has no significant effect on the Young's Modulus, but also alter the 200-μm scratch resistance. Core–shell fillers, i.e. silica particles coated with a low modulus polymeric shell, can be equivalent to non modified silica particles as far as the 200-μm scratch test is concerned, but they weakly improve the Young's modulus of the Glymo films, suggesting a poor resistance of filled coatings to small scratches.