Asymmetric Gemini surfactants as corrosion inhibitors for carbon steel in acidic medium: Experimental and theoretical studies

Asymmetric Gemini surfactants are a kind of novel surfactants with corrosion resistance ability, which are expected to be widely used in metal anti-corrosion during the pickling treatment. In this work, two asymmetric Gemini surfactants, N¹-(3-dodecanamidopropyl)-N³-dodecyl-2-hydroxy-N¹,N¹,N³,N³-tetramethylpropane-1,3-diammonium (surfactant Ⅰ) and N¹-(3-dodecanamidopropyl)-N³-tetradecyl-2-hydroxy-N¹,N¹,N³,N³-tetramethylpropane-1,3-diammonium (surfactant Ⅱ), were utilized as the corrosion inhibitor for A3 carbon steel in acidic medium. Weight-loss measurements indicated that the inhibition efficiency (η_w%) increased with increasing asymmetry degree, and the maximum values of η_w% for surfactants Ⅰ and Ⅱ reached 98.37% and 97.21% at 85 °C, respectively. The adsorption of these surfactants obeyed the Langmuir adsorption isotherm. The electrochemical measurements suggested that the two surfactants would serve as mixed-type inhibitors. The results obtained from scanning electron microscope (SEM), atomic Force Microscope (AFM) and X-ray diffraction characterizations (XRD) were in accordance with the experimental results that surfactants Ⅰ and Ⅱ are effective inhibitors for the metal in acidic medium. The quantum chemical study and Molecular dynamics (MD) simulation further supported the experimental results and provided insight into a deeper understanding of the inhibition mechanism of asymmetric Gemini surfactants.