Effect of various terminal groups on long-term protective properties of aromatic SAMs on copper in acidic environment

Abstract

The effect of several p-substituent groups (–F, –CH3, –OH, –COOH, –NHCOCH3) on the performances and the stability of aromatic monolayers on copper has been studied. All the results agreed indicating that such aromatic films are very stable and effective as corrosion inhibitors even in harsh conditions (aerated H2SO4 0.5M). Nevertheless, while XP spectroscopy showed an excellent chemical stability for all the layers regardless the terminal groups, EIS measurements highlighted notably different protective properties and durability for the various SAMs. Such passivation depends not only on the hydrophobicity of the terminal group but, surprisingly, also on the electronic effect of the substituent on the ring as well. In particular, molecules having an electron-withdrawing substituent showed good passivity at first, a steep increase of their protective properties following the exposure to the electrolyte but a relatively poor stability. The presence of an electron-donating substituent, on the other hand, led to relatively poor initial protection, a slow reorganization but an exceptionally long durability.