Interfacial mechanisms and performance of a diimine schiff base inhibitor for carbon steel in 1M HCl: Advanced modelling coupled with experimental characterization

This work establishes processing–properties–performance relationships for a diimine Schiff-base inhibitor, 4,4′-bis[4-diethylaminosalicylaldehyde]diimino diphenylmethane (LNEt), protecting XC48 carbon steel in 1 M HCl by coupling advanced modelling with electrochemical and surface characterization. Density functional theory (DFT) resolves electronic structure and reactivity indices, indicating enhanced electron-transfer propensity upon protonation in acid. Complementary molecular dynamics (MD) simulations highlighted preferential horizontal adsorption patterns and high surface affinity, suggesting robust and uniform molecular coverage on the metal substrate. Experimentally, weight loss analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) confirmed these computational insights, demonstrating a maximum inhibition efficiency of approximately 89 % at an optimal inhibitor concentration (10⁻⁴ M) at room temperature. The inhibitor exhibited mixed-type behavior with substantial cathodic reaction suppression. Surface characterization techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements, corroborated the formation of a uniform, compact, and hydrophobic protective film. These findings, aligning closely with the Langmuir adsorption isotherm, reinforced the dominant role of chemisorptive interactions. By integrating advanced characterization with DFT/COSMO-RS/MD analyses, the study provides a mechanistic bridge from molecular descriptors to interfacial film properties and corrosion performance, informing interphase-engineering strategies for steels in aggressive acidic processing environments. • DFT calculations reveal crucial frontier orbitals governing Schiff base reactivity. • COSMO-RS and σ-profiles clarify solvation effects enhancing inhibitor adsorption. • MD simulations confirm stable parallel adsorption orientation onto Fe(110) surface. • Correlation established between theoretical predictions and inhibition performance. • Surface analyses (SEM, AFM, contact angle) support electrochemical results.