Zwitterionic polymers as high-performance corrosion inhibitors: Ab-Initio quantum insights and experimental validation for iron-containing surfaces

A polymeric-zwitterionic corrosion inhibitor (PZCI) to reduce the corrosion rate of pristine or initially degraded iron surfaces exposed to an HCl acidic aqueous medium is proposed, and its performance was both quantum-theoretically and experimentally investigated. The adsorption of HCl on iron-containing surfaces such as pyrite, hematite, siderite and pure iron was studied through Density Functional Theory (DFT) and compared with that of PZCI. DFT predicts that the quaternary-amine and carboxylate functional groups of PZCI prevent HCl from reaching the surfaces by capturing it beforehand. Likewise, the PZCI's carboxylate oxygens bind to the degraded surfaces' exposed Fe atoms, completing the octahedral chalcogen coordination of the latter and shielding them through repulsion of approaching chlorine anions. The PZCI surface adsorption is moreover strengthened because the alkyl tail's carbon double bonds C=C are also linked by surface Fe atoms. Consequently, it is predicted that PZCI must efficiently protect surfaces at initial degradation stages against subsequent corrosion. This prediction was experimentally verified on a steel coupon immersed in HCl aqueous solutions with and without lab-synthesized PZCI, and it was found that the corrosion rate was reduced when PZCI was used.