Poly(3,4-ethylenedioxythiophene) on self-assembled alkanethiol monolayers for corrosion protection

Self-assembled monolayers (SAMs) of octanethiol and dodecanethiol were used to modify the stainless steel substrates for electrodepositing poly(3,4-ethyledioxythiophene) (PEDOT), a well known polythiophene derivative. Although the influence of the alkanethiol monolayers on the morphology and topology of micrometric (thickness: 2.25-2.35 mu m) PEDOT films is practically negligible, they increase significantly the ability to store charge and the adherence. In contrast, treated substrates not only enhance the electrochemical properties of ultra-thin PEDOT films (thickness: 150-350 nm) but also affect significantly the thickness, roughness, porosity, morphology and topology. Such changes depend on both the length of the alkyl chain in the alkanethiol and the incubation period used for the preparation of the SAMs. Finally, the protection against corrosion imparted by PEDOT films deposited on treated substrates has been examined and compared with that obtained using PEDOT deposited on bare stainless steel electrodes. Inhibition of the corrosion in a 3.5% NaCl solution was found to be considerably higher when PEDOT is deposited on treated electrodes, which has been attributed, in addition to the barrier effect produced by the SAMs, to the structural changes induced at the first stages of the electropolymerization.