Theoretical insights into the structural characteristics and inhibition mechanisms of quaternary ammonium salt and imidazolium-based ionic liquid: DFT and MD simulations

Abstract

Quaternary ammonium and imidazolium-based corrosion inhibitors have attracted extensive research interest due to their effectiveness. However, despite extensive investigations into the correlation between functional groups and inhibitor adsorption modes, the microscopic mechanisms underlying the corrosion inhibition on metal surfaces remain inadequately understood. This study investigates the inhibition performance of an acidic imidazolium ionic liquid (IBIL) and a quaternary ammonium derivative (QAS), each containing a ten-carbon alkyl tail, using quantum chemical calculations and molecular dynamics (MD) simulations to predict their inhibition efficiency and adsorption behavior, based on DFT and MD simulations. The results indicate that the inhibition efficiency follows the order: IBIL > QAS for the Fe(100) surface in CO₂-saturated 1 wt% NaCl solutions, consistent with previous experimental data. Different molecular structures of inhibitors lead to distinct adsorption behaviors on the steel surface. QAS adheres via a direct electron adsorption model, while IBIL adopts a cyclic electron adsorption model, involving electron donation and acceptance from different functional groups. This study not only enhances the understanding of inhibition mechanism but also provides valuable insights for the rational design and industrial application of high-performance inhibitors.