Wear-resistant and transparent acrylate-based coating with highly filled nanosilica particles

Hybrid nanocoatings are one of the most attractive topics in nanomaterials which have achieved the transition from fundamental researches to practical applications. In the present study, a urethane–acrylate oligomer was mixed with varied concentrations of nanosilica particle sol, spin-coated onto polycarbonate substrate and finally cured by ultraviolet (UV) rays. The morphology, mechanical properties and wear resistance of the resultant hybrid coatings were systematically investigated. Infrared spectroscopy (IR) analysis was performed to determine the eventual curing extent of the mixtures studied. The transmission electron microscopy (TEM) micrographs revealed almost perfect dispersion of the nanosilica particles within organic matrices, which ensured the excellent transparence of the hybrid coatings. Nanoindentation was further conducted to determine the mechanical properties, i.e. hardness, elastic modulus and their nanoparticle loading dependence. The short-term wear resistance was characterized by a pencil hardness tester. Moreover a universal micro-tribotester (UMT) was applied to investigate the long-term performance. As a result, about 20% decrease in coefficient of friction (COF) was achieved by the coating filled with 40 wt% nanosilica particles, compared to that of the unfilled coating. Under the same fretting test conditions, the wear rate in terms of wear volume of the hybrid coating containing 40 wt% nanoparticles was about 70 times lower than that of the neat coating, confirming the wear-reduction capability of the nanoparticles. The related wear mechanisms were discussed based on worn-surface observations.