Alkanethiol Self-assembled Film Corrosion Protection Performance Of Electrochemical Research

Self-assembled monolayers (SAMs) are highly ordered, and close-packed molecular films, which form through spontaneous chemisorption of active molecules onto solid surface. SAMs are similar somewhat to a kind of ultrathin hydrophobic coatings, but the advantages of SAMs over common organic coatings are: (i) the ultrathin film forms through a quite simple chemisorption process and strongly adheres to the metal surfaces and (ii) the film thickness can be controlled at the nanometer level by selecting adsorbates and (iii) the presence of the film will not significantly alter the appearance or most other characteristics of substrate except hydrophilicity of metal surfaces. Therefore, SAMs provide a great possibility to protect the metal substrate from corrosion under different corrosive environments.Copper is a metal widely used in chemical and electronics industries, and it is therefore of both theoretical and practical importance to study the protection ability of alkanethiol SAMs to the underlying copper substrate in corrosive solutions.The self-assembled monolayers (SAMs) of three n-alkanethiols, 1-octadecanethiol (C18SH), 1-dodecanethiol (C12SH), and 1-hexanethiol (C6SH), were formed on fresh, oxide-free copper surfaces pretreated by nitric acid etch. The surface properties of the alkanethiol modified copper electrode in chloride-containing solutions were electrochemically characterized. The polarization measurements have shown that alkanethiol SAMs onto copper were able to protect effectively the underlying copper against corrosion. The cyclic voltammetric results, together with FTIR measurements, showed alkanethiol SAMs had quite good anodic inhibition at the lower anodic potentials, but this inhibition action gradually lost because of removal of SAMs from the copper substrate with the increase of anodic potentials.The corrosion protection ability of three alkanethiol SAMs was evaluated in 0.2 mol dm^-3 NaCl, 0.2 mol dm^-3 HCl and 0.2 mol dm^-3 H₂SO₄ solutions by using electrochemical impedance spectroscopy (EIS) method. The SAMs act as the hydrophobic barrier layer, which effectively prevents the copper substrate from contacting corrosive ions, thereby inhibiting the copper corrosion to a considerable...