Corrosion-resistant omniphobic coating for low-carbon steel substrates using silica layers enhanced with ethylenediamine tetraacedic acid

The present work develops a highly liquid repellent, <i>i.e.</i> omniphobic, coating designed specifically for metallic substrates like low carbon steels and evaluates its potential as a barrier to corrosion. Polydimethylsiloxane (PDMS) chains are grafted to an intermediary silica layer <i>via</i> the hydrolysis and polycondensation of a difunctional chlorosilane monomer, resulting in a contact angle hysteresis of ∼3° when deposited on unpolished low carbon steel substrates. However, the use of chlorosilanes to fabricate the omniphobic PDMS can corrode steel. To circumvent this, the coating uses a phosphate buffer solution to partially neutralize the silica precursor solution, and ethylenediamine tetraacedic acid (EDTA) to passivate any released Fe ions. The inhibition of corrosion is evidenced visually and by unchanging surface metrology parameters even after two months following coating deposition. Potentiodynamic polarization data indicate that the omniphobic layer provides a barrier to water ingress, as evidenced by a current density of ∼10^-6 A cm^-2, two orders of magnitude lower than the steel coated with the silica but without the PDMS chains. Electrochemical impedance spectroscopy data indicates the absence of an inductive loop (<i>i.e.</i> no ongoing corrosion) and a high polarization resistance of 40 000 Ω cm² for the omniphobic coating. This work not only indicates that omniphobic grafted polymer chains like PDMS exhibit anti-corrosion properties, but also provides a method for depositing such coatings onto metals without corroding the substrate, even when using chlorosilane precursors that evolve hydrochloric acid.