Engineering Advanced Environmentally Friendly Corrosion Inhibitors, Their Mechanisms, and Biological Effects in Live Zebrafish Embryos

Carbon steel is one of the most used construction materials and makes up the bulk of steel production in the world. However, this alloy is vulnerable to corrosion, which reduces its safety and costs trillions of dollars worldwide in terms of corrosion protection and infrastructure maintenance. Corrosion inhibitors are among the cheapest and most effective methods to minimize corrosion and maximize the shelf life of this ubiquitous alloy; however, they are often harmful to the environment. Currently there are no reports in terms of engineering design methodology to develop highly effective, advanced corrosion inhibitors. The possible synergistic behavior of a surface-active quaternary ammonium with a tailored carboxylate compound provides a rational molecular design toward delivering corrosion inhibitors to a metal surface through controlled speciation in solution. Here we show how entrapment and delivery of the anion inhibitor through speciation and micellar formation can lead to high inhibition efficiency, as determined by potentiodynamic polarization and electrochemical impedance spectroscopy. In particular, we demonstrate how NMR spectroscopy, pfg NMR diffusion measurements, and Cryo-TEM, taken together with molecular dynamic simulations, can reveal the micellar formation and its concentration dependence, with wormlike micelles evident at higher concentrations correlating with a dramatic increase in viscosity. This new organic corrosion inhibitor, cetrimonium 4-ethoxy cinnamate, provides significantly higher corrosion inhibition efficiency compared with the 4-hydroxy cinnamate analogue and with reduced toxic impact in the zebrafish embryo compared to the surface active CTAB often used as an antimicrobial.