Molecular-Level Investigation of TiO2/HALS Hybrid Nanocomposites for UV-Resistant Fusion-Bonded Epoxy Coatings: Correlating Interfacial Interactions with Surface Protection and Mechanical Durability

The primary objective of this study is to develop highly UV-stable fusion-bonded epoxy (FBE) coatings through the incorporation of TiO2/hindered amine light stabilizer (HALS) hybrid nanocomposites at different filler loadings. The resulting coatings were comprehensively characterized to establish the relationship between interfacial interactions and their protective performance. X-ray photoelectron spectroscopy (XPS) confirmed the successful immobilization of HALS on the TiO2 surface through Ti–O–C coordination and hydrogen-bond-assisted interactions, demonstrating the formation of a stable organic–inorganic interface. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements conducted during 30 days of immersion in 3.5 wt % NaCl solution revealed a significant improvement in the corrosion resistance of the hybrid FBE coatings. Accelerated weathering for 1000 h further demonstrated effective UV durability, while interfacial adhesion, instrumented indentation, and scratch resistance tests confirmed enhanced coating adhesion, hardness, modulus retention, and resistance to surface damage after UV exposure. Furthermore, molecular dynamics (MD) simulations revealed stronger interfacial interactions between the TiO2/HALS hybrid nanocomposite and the FBE matrix, accompanied by reduced fractional free volume and improved interfacial compatibility, providing atomistic insight into the synergistic enhancement of UV stability, mechanical durability, and corrosion protection. These findings demonstrate that the TiO2/HALS hybrid nanocomposite is an effective multifunctional reinforcement for developing durable FBE coatings for long-term atmospheric and marine steel protection.