Experimental and Theoretical Studies of the Corrosion Inhibition Performance of Fatty Acid-based Ionic Liquids for Mild Steel in 1 M HCl: Effects of the Varied Alkyl Chain Length in the Anionic Group

Abstract

Five fatty acid-based ionic liquids (FAILs) with various anionic alkyl chain lengths are synthesized, namely methyltrioctylammonium butyrate ([N8881][C4:0]), methyltrioctylammonium caproate ([N8881][C6:0]), methyltrioctylammonium octanoate ([N8881][C8:0]), methyltrioctylammonium laurate ([N8881][C12:0]), and methyltrioctylammonium palmitate ([N8881][C16:0]), to investigate the potential effects of anionic alkyl chains on their corrosion inhibition property for mild steel in 1 M HCl solution via X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, contact angle measurements, electrochemical measurements, and weight loss measurements. The results reflect that the FAIL inhibitor can adsorb on the surface of mild steel to form a protective film and effectively inhibit the corrosion. [N8881][C8:0] exhibits the optimal inhibition efficiency (96.94%) in comparison to [N8881][C4:0] (80.73%), [N8881][C6:0] (89.34%), [N8881][C12:0] (90.69%), and [N8881][C16:0] (74.42%). It is speculated that the varied anionic alkyl chain length may change the intensity of the protective film to affect the inhibition efficiency. The in-depth analysis by molecular dynamic simulation confirms that [N8881][C8:0] with the same anionic and cationic alkyl chain lengths shows the most ordered and compact film on the mild steel surface. The present study focuses on the effects of the anionic alkyl chain on the corrosion inhibition performance and provides novel insights into the design and development of effective and eco-friendly ionic liquids as corrosion inhibitors.