Effect of Alkyl Chain Length on the Surface Properties and Corrosion Inhibition Performance of Imidazoline Gemini Compounds

Four imidazoline gemini compounds (GI-C₁₁, GI-C₁₃, GI-C₁₅, GI-C₁₇) were synthesized by reacting imidazoline quaternization intermediates with four different alkyl chain length fatty acids (dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid), diethylenetriamine and dimethyl carbonate as raw materials. The surface properties of four gemini compounds were studied using hanging drop method and water separation method. The corrosion inhibition performance was evaluated using electrochemical testing, SEM-EDS, and the adsorption behavior was studied. The results indicate that the series of twin compounds had good surface performance and corrosion inhibition properties, and the surface and corrosion inhibition properties increased with decreasing chain length. Among them, GI-C₁₁ had the best performance, with the lowest surface tension of its aqueous solution (24.55 mN · m^-1) at the critical micelle concentration (0.266 mmol · L^-1). The corrosion inhibition rate of 50 mg·L^-1 GI-C₁₁ on N80 steel (50 ℃, 5% HCl, corrosion for 4 hours) was 97.46%. The four types of corrosion inhibitors are all mixed corrosion inhibitors that mainly inhibit the anode, and the corrosion inhibition effect increases with the increase of corrosion inhibitor dosage. Its adsorption on the surface of N80 steel is a mixed adsorption involving chemical and physical adsorption which follows the Langmuir adsorption isotherm.