Prevention of passive film breakdown on iron by coverage with one-dimensional polymer films of a carboxylate ion self-assembled monolayer modified with alkyltriethoxysilanes

A film composed of a one-dimensional polymer was fabricated by modification of a 16-hydroxyhexadecanoate ion HO(CH₂) ₁₅CO₂^- self-assembled monolayer (SAM) adsorbed on a passivated iron electrode with octadecyltriethoxysilane C ₁₈H₃₇Si(OC₂H₅)₃. The pitting potential, E_pit of the passivated electrode coated with this film was measured by anodic polarization in a borate buffer solution containing 0. 1 M of Cl^-. The E_pit value of the electrode coated with the film was markedly shifted from the value of the bare electrode in the positive direction, indicating prevention of passive film breakdown. No breakdown occurred over the potential range of passive region in some cases. Structure of the modified SAM was discussed by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement of the electrode surface covered with the film. Suppression of Cl^- accumulation at a defect of the passive film was revealed by electron-probe microanalyses of the surfaces uncoated and coated with the SAM modified with octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃ after anodic polarization in the borate buffer containing Cl^-.