Comparative study on the optical, surface mechanical and wear resistant properties of transparent coatings filled with pyrogenic and colloidal silica nanoparticles

We applied two kinds of silica nanoparticles, i.e. colloidal and pyrogenic ones, to improve the performance of transparent coatings on polymer substrates. The urethane–acrylate oligomer was mixed with varied concentrations of silica nanoparticles, spin-coated onto polycarbonate substrate and finally cured by ultraviolet rays. The resultant thickness of the coatings can be controlled in the range of 20–30 μm. The transmission electron microscopy revealed that both silica nanoparticles presented different dispersion states, i.e. mono-dispersion for the colloidal nanoparticles and floc-like dispersion for the pyrogenic ones. In comparison with the colloidal nanoparticles filled coatings, the pyrogenic ones exhibited much improved modulus, hardness and wear resistance, but slightly decreased optical properties such as transmittance, haze and gloss. The nanoparticle morphology, amorphous structure, dispersion state and particle–matrix interfacial bonding relating to these properties were discussed in the present study.