| Metal corrosion is a very common phenomenon in different fields of national economy. The problems induced by corrosion exist at various positions where the materials could be used. The stainless steel is one of the most widely used metals in the daily life, agriculture-industrial production, and so forth. However, the"stainless"is relative. The stainless steel can be rusted at certain conditions, especially in the strong corrosion medium such as seawater. The corrosion of stainless steel could bring serious financial losses to life and production. Hence, the corrosion and protection of stainless steel is a fundamental research subject to be solved in the related fields. Surface modification is a pretty important method to improve the corrosion resistance. It is a meaningful research to prepare strong adhesive and environment friendly films on stainless steel surface.Inspired by the bio-adhesion principle, dopamine was chosen as the research object, which has the same structure functional group of the mussel adhesive proteins secreted by mussels. The polydopamine films were fabricated by dipping the stainless steel substrate into an aqueous alkaline dopamine solution. The possible reaction mechanism and temperature effect were also studied. The membranes were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), surface reflection Fourier transform infrared spectrum (SR-FTIR), UV-visible spectrum. SEM shows similar morphologies of polydopamine films prepared at 24℃and 34℃. They cover the entire surface and form island-like structure in local area. Both EDS analysis and SR-FTIR spectra demonstrate the similarity between the polydopamine films prepared at different temperatures. Meanwhile, the results of UV-visible spectrum imply that the polydopamine film prepared at 34℃is much thicker, which supports well the EDS results. Based on the Gaussian 98 program, the polymerization reactions of dopamine in solution were analyzed by the LUMO energies, simulated infrared spectrum and HOMO-LUMO energy gaps of selected structure models calculation. The calculation results explain well the preferable change from dopamine molecule to indolequinon molecule, following it produce the polymerization reaction and evolve into diindolequinon structure. The line growth is difficult and two-dimensional growth is easy. The possible interfacial reaction mechanism was also discussed based on the molecular orbit analysis of melanin cluster. The unoccupied molecular orbital charge of the selected molecule focuses on the one side including more oxygen atoms. Additionally, the long-term impedance characteristics of polydopamine were investigated in simulated seawater (3.5% NaCl solution) by Electrochemical Impedance Spectroscopy (EIS), implying good durability, strong adhesive force and superior corrosion resistance of polydopamine films on 304 SS. Especially the polydopamine film prepared at 34℃has superior corrosion resistance with the increase of time.In order to improve the protection effect, the composite film was prepared on the 304 SS substrate. To our knowledge, it is the first time that SAMs of 6-aminohexanol were grafted on the 304 SS substrate assisted with the preferential adhesion of polydopamine. Optical microscope, SEM and EDS analysis indicate the successful graft on the substrate. EIS and polarization curves also demonstrate the significant corrosion resistance. The inhibition efficiency of the 6-aminohexanol/polydopamine composite films reaches up to 99%. Accordingly, this study provides an efficient and environmentally friendly method for the functionalization of stainless steel surface for corrosion protection. Furthermore, the exploratory experiment of the further application was probed and ATRP initiator was successfully grafted on the substrate, which serves as a platform for further modification. |
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