Study of organic coating/metal behavior at microscopic level

Organic coatings have been recognized as efficient corrosion protective layers for carbon steelsubstrates [1, 2]. During recent years, extensive experimental efforts demonstrated the potentialapplications 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-curedbisphenol A epoxy resin (Figure 1 (a)), to form coating layers above carbon steel (represented byFeO 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 allepoxy resin adsorbate molecules moved toward the crystallographic plane (100) in both FeO andFe3O4 adsorbents, and become localized in vicinity of surface. These observations quantitativelyindicate the fact that aminoamide-modified epoxy resins have strong intermolecular interactionswith the iron oxide. The adsorption affinity of epoxy coating strongly attached to surfaces of FeOand Fe3O4 was quantitatively investigated using binding energy parameter (ΔEbinding). The bindingenergies 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 epoxyadsorbate and oxide surface (100) in considered iron oxides. Adsorption behavior of aminoamideconjugated epoxy resin was further examined through atomic concentration profiles above surfacesbefore and after MD simulations. As shown in panel (iv) in Figure 2, the final time-averagedconcentration profiles for oxygen and nitrogen atoms (Of and Nf) occurred at lower distances fromsurfaces as compared to initial concentrations (Oi and Ni), which again quantitatively describes thatmodified epoxy resin positioned neighboring iron oxide surfaces. All these insights firmly provethe capability of poly (aminoamide) cured epoxy resin materials to serve as effective coatings oncarbon steel surfaces when exposed to corrosive electrolytes.

Keywords:

Organic coating , Metallic substrate , Corrosion , Computation