First-Principles Calculation on the Adsorption of Ethylene-Acrylic Acid Molecules on Chromium Oxide Surfaces

Currently, hybrid materials composed of metals and polymers are used in various fields, including aerospace and biomedicine. Specifically, laminated strips composed of chrome-plated steel and ethylene-acrylic acid (EAA), which are the focus of this study, are used as protective materials for fiber-optic cables. Understanding the bonding mechanism between these materials is essential for enhancing the cables' long-term stability. Previously reported experimental studies have suggested that, at the adsorption interface between chrome-plated steel and EAA molecules, two different types of coordination bonds are formed in addition to hydrogen bonding: (O)-C-O-Cr, which is monodentate, and -C-(O-Cr)₂, which is bidentate. Therefore, in the present study, we used density functional theory (DFT) to evaluate the energies associated with the adsorption of EAA molecules onto Cr₂O₃ (001) and (012) surfaces with a thin layer of chromium hydroxide, as well as those associated with the adsorption of EAA molecules onto pure Cr₂O₃ (001) and (012) surfaces without the hydroxide layer. The DFT calculations confirmed the bonding mechanisms at the adsorption interfaces suggested by previous experiments, including hydrogen bonding, monodentate coordination, and bidentate coordination. Structural optimizations revealed that adsorption structures involving coordination bonds were energetically more stable than those involving only hydrogen bonding. On the (012) surface with the hydroxide layer, however, DFT results showed that no coordination bonds were formed between the EAA molecules and the surface, which was attributed to the coordination saturation of surface Cr atoms by hydroxide groups. The findings provide a foundation for developing more robust protective materials for fiber-optic cables.