Effects of Oil Viscosity on the Anti-Corrosion and Self-Healing Properties of Oil-Impregnated Nanoporous Anodic Aluminum Oxide

Abstract

Oil-impregnated nanoporous metal oxide surfaces such as anodic aluminum oxide showed significantly enhanced corrosion resistance and durability compared to hydrophilic or hydrophobic/superhydrophobic surfaces with no oil impregnation. Especially, the efficacy and durability of the oil-impregnated porous surfaces depend on the stability and retentivity of oil within the nanopores, where nanopores serve as reservoirs to hold the water-repelling and corrosion-protective oil in liquid phase. Previously, we demonstrated that the shape of nanopores should be an important factor to influence the stability and retention of oil. For example, it was demonstrated that the bottle-shaped nanopore featured with a smaller pore diameter at the upper layer than at the lower layer could immobilize the oil in the nanopores more stably than simply vertical nanopores, showing the greater corrosion resistance and robustness. In this study, we further report the effects of the oil viscosity on corrosion behaviors by testing bottle-shaped nanoporous anodic aluminum oxide surfaces impregnated with perfluorinated oils having various viscosities. Potentiodynamic polarization, salt fog and salt-water immersion tests show that the bottle-shaped nanoporous anodic aluminum oxide surfaces impregnated with more viscous oils result in the greater corrosion resistance and durability due to the enhanced oil retentivity. Despite the increased viscosity, the liquid oil still maintains the fluidity so that it fills physically damaged areas and allows the oil-impregnated surfaces to keep the self-healing capability. The result suggests that the anti-corrosion efficacy and durability of oil-impregnated porous surfaces can be optimized by modulating not only the pore geometry but also the oil viscosity.