Synthesis and evaluation of nonionic surfactants based on dimethylaminoethylamine: Electrochemical investigation and theoretical modeling as inhibitors during electropolishing in-ortho-phosphoric acid

Three non-ionic surfactants had synthesized through one simple direct reaction between N, N-dimethylethylenediamine and three fatty acids: octanoic, palmitic and oleic acid. The chemical structures of the synthesized non-ionic surfactants had been confirmed by FTIR & ¹HNMR spectroscopy. The surface and thermodynamic behavior of the surfactant were determined at different temperatures based on surface tension (γ) measurments. The critical micelle concentration (CMC) is dependent on both of the hydrophobic chain length and solution temperature. The change in free energy of micellization (∆G°_mic) and adsorption (∆G°_ads) referring that the synthesized surfactants favor adsorption at interfaces than constructing a micelle. The performance of the synthesized surfactants on the dissolution behavior of carbon steel in 8 M H₃PO₄ acid have been investigated at temperature range 15 to 45 °C via weight loss and polarization measurements. The dissolution rate (limiting current I_L) decreases with increasing the surfactants concentrations confirming a mass transport-controlled process and a salt-film mechanism. Polarization curves showed that the prepared surfactants are good anodic inhibitors and the adsorption on the carbon steel surface obeys the Langmuir isotherm. The examining the surface morphology, topography and brightness of the carbon steel in a 8 M H₃PO₄ containing the synthesized surfactants using scanning electron microscope (SEM), atomic force microscope (AFM) and gloss meter, disclosed the adsorption of the prepared inhibitors surfactant on the steel surface. The data obtained from theoretical calculations support empirical results.