Composition-dependent cooperative adsorption of benzimidazole films on copper surfaces: Linking interfacial organization to chloride corrosion protection

Designing molecular films with controlled interfacial organization is a promising strategy for improving the durability of metallic materials in chloride-containing environments. In this work, two benzimidazole derivatives, 5-bromo-4,6-dinitro-2-(trifluoromethyl)-1H-benzo[ d ]imidazole (AB13) and 5-bromo-2-ethyl-4,6-dinitro-1H-benzo[ d ]imidazole (AB14), were investigated individually and as mixed formulations for copper protection in 3.0 wt% NaCl. Electrochemical impedance spectroscopy and potentiodynamic polarization showed that both molecules reduce copper corrosion, with AB14 exhibiting superior individual performance. The AB14-rich P5 mixture achieved the highest inhibition efficiency, exceeding 95%, owing to improved interfacial coverage and film compactness. SEM and AFM analyses confirmed that the inhibited surfaces were smoother and more homogeneous, with the P5 system producing the most protective surface state. Adsorption and thermodynamic analyses indicated spontaneous interaction of both inhibitors with the copper surface. DFT calculations identified heteroatoms and π-electron-rich regions as the main adsorption centers, while Monte Carlo and molecular dynamics simulations on Cu(111) revealed stable, nearly parallel adsorption configurations. RDF and MSD analyses further showed stronger Cu-O interactions and reduced molecular mobility for AB14, explaining its dominant role in the mixed film. Synergistic parameter analysis indicated that the AB13/AB14 system does not follow classical synergism, but rather a composition-dependent cooperative adsorption mechanism, where AB14 governs primary surface anchoring and AB13 contributes to residual surface coverage and interfacial organization. This study provides surface-level insight into the rational design of mixed inhibitor films for copper protection in chloride media.