Corrosion inhibitors: design, performance, and computer simulations

The development of a methodology to predict the performance of a corrosion inhibitor (CI) using specific types of modeled and experimental surfaces and their subsequent estimation is presented. For previously reported imidazoline CIs, the theoretical partition coefficients and molecular volumes were calculated, providing a guide for molecular engineering of new imidazolines. The new CIs, N-[2-(2-alkyl-4,5-dihydroimidazol-1-yl)ethyl]alkylamides and N-[2-(2-alkyloylaminoethylamino)ethyl]alkylamides, were designed, prepared, and their theoretical partition coefficients and molecular volumes calculated. These indexes were correlated between tested and prototype CIs to select the best ones for the corrosion inhibition tests. The inhibition efficiencies were measured through potentiodynamic polarization curves (PPC), linear polarization resistance (LPR), and weight loss measurements (WLM) for SAE-1010 and SAE-1018 steels. The leading molecules were 1-(2-decylaminoethyl)-2-decylimidazoline and 1-(2-dodecylaminoethyl)-2-dodecylimidazoline with WLM efficiencies (steel 1010), of 62.8 and 78.9%, respectively. The efficiencies for the PPC/LPR tests (steel 1018) were 97 and 94%. To understand the mechanism of action of CIs, a simple model is suggested for the growth of self-assembled monolayers of CIs on a crystalline substrate. This model takes into account the amphiphilic nature of the inhibitor molecule on the adsorption process. Despite the simplicity of the model, the Monte Carlo simulations reproduce qualitatively many of the experimentally observed features involved in the formation of monolayers and provide a tentative explanation for the mechanism of corrosion inhibition.