Fabrication of a Silica–Silica Nanoparticle Monolayer Array Nanocomposite Film on an Anodic Aluminum Oxide Substrate and Its Optical and Tribological Properties

The fabrication and properties of silica nanoparticle monolayer arrays (SNMAs) immobilized on silica films on nanoporous anodic aluminum oxide (AAO) substrates by polymerization of silicic acid and a two-step spin-coating technique are reported. Reflection spectra of the obtained silica–SNMA nanocomposite films on AAO substrates were almost the same as those of the original AAO substrate. The coefficient of friction at an applied load of 0.98 N under dry conditions for a film fabricated under optimal conditions was significantly decreased by 76% with respect to that without a silica–SNMA nanocomposite film on an AAO substrate. The results also showed a lower coefficient of friction than that for MoS2 nanoparticles (commonly used for self-lubricating films) deposited on an AAO substrate. We demonstrate that the silica–SNMA nanocomposite film with an optimal nanoroughness, thickness, and wear resistance can be used as a novel coating film for AAO substrates with both a high color degree of freedom and a low coefficient of friction at a high applied load (ca. 1 N).