Interfacial infiltration-driven structure-property relationships in PCL/graphene nanoplatelet nanocomposite coatings on anodized TiO2 nanotubes

This study examines the structure-property relationships of polycaprolactone (PCL)/graphene nanoplatelet (GNP) nanocomposite coatings infiltrated into anodized TiO2 nanotubes formed on Ti-6Al-4V ELI alloy. Anodization produced a homogeneous nanotubular oxide layer with an average diameter of 72.98 ± 5.6 nm and a length of 1.13 ± 0.03 μm, which served as a porous scaffold for polymer infiltration. The PCL concentration was optimized in the range of 4-7 wt.%, and 7 wt.% was selected as the matrix composition for nanocomposite design. GNPs were incorporated at 0.3-1.0 wt.% to evaluate nanofiller-induced structural and functional changes. Among the investigated formulations, the coating containing 0.5 wt.% GNP exhibited the most pronounced structural modification, indicating enhanced polymer-filler interaction. Cross-sectional analyses confirmed that both PCL and PCL/GNP phases penetrated the nanotubular architecture rather than forming only superficial overlayers. The PCL/GNP nanocomposite coating exhibited improved corrosion and tribocorrosion performance while preserving hydrophilicity and promoting hydroxyapatite formation. Overall, the results demonstrate that surface performance is governed predominantly by interfacial infiltration and nanocomposite organization rather than coating composition alone.