Understanding the relationship between the structural properties of three corrosion inhibitors and their surface protectiveness ability in different environments

Abstract

All-atom molecular simulations and chemical quantum calculations were used to understand the effect of the environment on the surface adsorption of corrosion inhibitor (CI) molecules. Three CIs abbreviated: TEPA, iTEPA and HC-iTEPA studied in this work, were selected to systematically investigate the influence of the alkyl tail, N-pendant group, imidazoline and benzene rings, on the CIs adsorption behavior. A relationship is provided between their structural properties and their surface protectiveness ability in different environments. Chemical quantum calculations revealed the electron distribution in inhibitors structures, indicating their ability to accept/donate charges from the Fe atoms in vacuum and in water solvation. The quantum molecular parameters in water solvation anticipated higher electron transfer ability of iTEPA in aqueous conditions compared to TEPA and iTEPA, thus, leading to stronger adsorption on iron surface, corroborated by the molecular dynamics (MD) classical simulations. MD simulations showed that nearly 53%, 39%, 59% reduction in adsorption energies was detected for single inhibitor molecule of TEPA, iTEPA, and HC-iTEPA shifting from water to CO2-saline media, respectively. The formation of water double adsorption layer contributed to decreasing the CIs adsorption energies by the larger surface separation distances spotted in the density profiles. Nevertheless, the multi-inhibitors study revealed strong adsorption of TEPA and iTEPA on the iron surface, while HC-iTEPA neglected cooperative adsorption and aggregated as a spherical-like micelle with lower surface coverage propensity. Radial distribution functions g(r) explored the preferential interactions of inhibitor-H2O and inhibitor-CO2 that guided the CIs adsorption conformation. Self-diffusivity coefficients of competing adsorbates with the three CIs were found to be one to two orders of magnitude lower near the interface than in the bulk.