Experimental and theoretical assessments of an innovative star-shaped polyamine surfactant designed for X-65 steel corrosion mitigation in acidic environment

The extant study introduces newly fabricated star-shaped polyamine surfactant (PAS) as a highly effective corrosion inhibitor for carbon steel (X-65) in 1.0 M HCl environment. The PAS was synthesized by reaction of dodecyl amine with maleic anhydride via ring-opening reaction forming a monomaleate amide that was esterified with triethanolamine to yield a star-shaped structure, followed by Michael addition reaction using diethylenetriamine. The chemical structures of PAS were confirmed by FT-IR and ¹HNMR. Surface tension measurements were employed to quantify the key surface properties of PAS. The inhibition performance was comprehensively evaluated through electrochemical techniques, surface characterization, and theoretical computations. Electrochemical impedance spectroscopy (EIS) revealed an exceptional inhibition efficiency of ~ 96% at an optimal concentration of 1000 µM, with the charge transfer resistance increasing significantly to 348.56 Ω cm². Potentiodynamic polarization (PDP) measurements demonstrated that PAS operated as a mixed-type inhibitor through suppressing both anodic and cathodic reactions. The inhibition mechanism was governed by the spontaneous adsorption of PAS molecules onto the X-65 surface, which follows the Langmuir adsorption isotherm suggesting a combination of physical and chemical adsorption. Surface morphology analysis utilizing scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM) provided direct evidence of the protective adsorbed film of PAS. Furthermore, theoretical assessments using density functional theory (DFT), and Monte Carlo simulations (MCs) successfully predicted the PAS active sites and its strong adsorption affinity onto the Fe surface, corroborating the experimental findings.