ρ-Substituted imine cationic surfactants as carbon steel corrosion inhibitors: Experimental and theoretical (DFT and MCs) approaches

In this study, we synthesized cationic surfactants based on ρ-substituted Schiff base compounds—S-12 (E)-N-dodecyl-N,N-dimethyl1-4-((P-olylimino)methy)benzene aminiumchloride) and SO-12 (E)-N-dodecyl-4-(((4-methoxyphenyl)imino)methyl)-N,N-dimethyl benzeneaminiumchloride. Their chemical structures were confirmed via FTIR and ¹HNMR spectroscopies. SO-12 decreased the surface tension of 1 M HCl (61 mN.m⁻¹) to 24.4 mN.m⁻¹. Weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements were employed to investigate carbon steel (CS) corrosion reactions in blank HCl and HCl containing the synthesized surfactants. The CS corrosion suppression actions of S-12 and SO-12 increased with increasing concentrations until they reached approximately 97 %. Adsorption of S-12 and SO-12 delayed the CS corrosion rate. The adsorption process fitted the Langmuir adsorption isotherm. The thermodynamic properties of the CS reaction are also discussed. The surface morphology and elemental analysis of the outer surface layer of CS were studied at the optimal concentration of SO-12 using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Theoretical results of S-12 and SO-12 agree with experimental data, confirming the effectiveness of S-12 and SO-12 as corrosion inhibitors. Moreover, S-12 and SO-12 have superior performance compared with previously reported cationic surfactants under the same test conditions.