Experimental and Theoretical Studies of Action Mechanism of an Octadecylamine-based Molecular Assembly on Mild Steel

A supramolecular complex CDDA was prepared based on beta-cyclodextrin (beta-CyD) and octadecylamine (ODA) . Four possible configurations of CDDA might coexist in the supramolecular system based on molecular dynamics simulation (MD) . The corrosion inhibition effect and mechanism of CDDA for Q235 steel in the condensate water was evaluated via dynamic weight loss potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), coupling with scanning electron microscopy (SEM), atomic force microscopy, contact angles, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared spectroscopy (ATR-FTIR) . The inhibition efficiency for mild steel in the condensate water could reach 94.1% with 1 mmol/L CDDA at 35 degrees C. The corrosion mechanism of mild steel in the condensate water was not altered in the presence of CDDA; however, both the anodic and cathodic processes were inhibited along with the elevated polarization resistance. CDDA could be treated as a mixed-type inhibitor with predominantly anodic dominant. The results of XPS and ATR-FTIR indicated that ODA could be released from CDDA at on the metal/solution interface and form a protective monolayer film. The adsorption process could be well fitted by the Langmuir adsorption isotherm. Molecular dynamics simulations provided the visual evidence of the assembly mechanism of CDDA on the mild steel surface. The release of ODA from CDDA and assembly mechanism on the steel/solution interface were verified by MD and quantum chemical calculations based on density functional theory.