Study of organic coating/metal behavior at microscopic level

Organic coatings have been recognized as efficient corrosion protective layers for carbon steel substrates [1, 2]. During recent years, extensive experimental efforts demonstrated the potential applications of organic anti-corrosive files based on epoxy resins [3-5]. Here, molecular dynamics (MD) simulations were applied [6] to computationally study the ability of aminoamide-cured bisphenol A epoxy resin (Figure 1 (a)), to form coating layers above carbon steel (represented by FeO and Fe3O4 iron oxides, (Figure 1 (b) and (c)). By comparing the initial and final structures (visualized in Figure 2) for cured epoxy resin over each iron oxide substrate, it is seen that all epoxy resin adsorbate molecules moved toward the crystallographic plane (100) in both FeO and Fe3O4 adsorbents, and become localized in vicinity of surface. These observations quantitatively indicate the fact that aminoamide-modified epoxy resins have strong intermolecular interactions with the iron oxide. The adsorption affinity of epoxy coating strongly attached to surfaces of FeO and Fe3O4 was quantitatively investigated using binding energy parameter (ΔEbinding). The binding energies of epoxy resin with FeO and Fe3O4 were -843.10 and -2539.02 kcal/mol, respectively. These negative values quantitatively confirm the interfacial interactions exist between epoxy adsorbate and oxide surface (100) in considered iron oxides. Adsorption behavior of aminoamide conjugated epoxy resin was further examined through atomic concentration profiles above surfaces before and after MD simulations. As shown in panel (iv) in Figure 2, the final time-averaged concentration profiles for oxygen and nitrogen atoms (Of and Nf) occurred at lower distances from surfaces as compared to initial concentrations (Oi and Ni), which again quantitatively describes that modified epoxy resin positioned neighboring iron oxide surfaces. All these insights firmly prove the capability of poly (aminoamide) cured epoxy resin materials to serve as effective coatings on carbon steel surfaces when exposed to corrosive electrolytes.