Carbon chain length effect on salt-free imidazoline corrosion and aggregation

A series of salt-free imidazoline surfactants with different carbon chains was synthesized. The products were characterized by Fourier transform infrared spectrum (FTIR), nuclear magnetic resonance hydrogen spectrum (¹H NMR), and nuclear magnetic resonance carbon spectrum (¹³C NMR). The corrosion inhibition effect of salt-free imidazoline inhibitors with different carbon chains was evaluated by the static weight loss method, the electrochemical method, and scanning electron microscope observation. The corrosion inhibition mechanism was analyzed by adsorption mode, and an energy-dispersive spectrometer was used to study the adsorption of corrosion inhibitors on the steel surface. Transmission electron microscope and dynamic light scattering were used to analyze the aggregation of surfactants. It was found that with the increase of the carbon chain, the corrosion inhibition efficiency of imidazoline increased first and then decreased, and the corrosion inhibitor aggregate increased. There are two explanations for the decrease of corrosion inhibition efficiency after the chain length is too long: when the carbon chain is too long, the bending of the carbon chain will lead to the adsorption layer of the surfactant on the steel surface is not close, and the adsorption capacity of the corrosion inhibitor on the surface of the steel sheet is weak when the carbon chain is too long. The long hydrophobic tail chain is entangled with each other, resulting in a larger aggregation of surfactant.