Nanoscale Electrochemical Mapping Reveals the Mechanistic Basis of Corrosion Inhibition in Functional Polymeric Coatings

Designer polyimide‐based functional coatings have been developed and applied to cold‐rolled closed‐annealed (CRCA) steel to impart anti‐corrosion properties. These polyimide coatings were synthesized from a single dianhydride, 4,4′‐(4,4′‐Isopropylidenediphenoxy) bis (phthalic anhydride) (BPADA), combined with either a single diamine or a blend of two diamines. The structural and morphological characteristics of these polyimide coatings were investigated using Fourier‐transform infrared, scanning electron microscopy, and atomic force microscopy. Among the synthesized coatings, the BPADA + ODA (0.7 equivalent) + Jeff D‐230 (0.3 equivalent), denoted as BO 7 J 3 , exhibited the highest corrosion resistance during prolonged immersion, followed by BO (BPADA + ODA) and other coating systems. Both electrochemical impedance spectroscopy (EIS) and salt spray test (SST) analyses consistently demonstrated that the BO 7 J 3 coating possessed superior corrosion resistance among all evaluated systems. Time‐dependent EIS analysis further indicated that BO 7 J 3 and BO coatings are impermeable to corrosive ions, revealing a single capacitive loop up to 50 h, which signifies high barrier resistance to corrosive ions. The high corrosion resistance of BO 7 J 3 and BO coatings was also corroborated by frequency‐modulated Kelvin probe force microscopy, attributing this performance to their high surface nobility. Additionally, their lower tendency to corrode in an aqueous sodium chloride electrolyte solution was confirmed through open‐circuit potential studies.