Morphology-Dependent\nCorrosion Inhibition and Self-Healing\nProperties of Polypyrrole and Indigo Carmine Composites on Carbon\nSteel 1018 in a Saline Environment

The aim of this research is to explore the effectiveness\nof epoxy-resin@polypyrole\ncomposites as a corrosion inhibitor when applied as a coating on carbon\nsteel 1018 in a 3.5 wt % sodium chloride electrolyte solution. The\nanticorrosion properties of these composite coatings can be optimized\nby manipulating their morphology. To investigate how modifications\nin the structure of epoxy resin coatings impact their ability to inhibit\ncorrosion, three distinct forms of polypyrrole nanoparticles/indigo\ncarmine structures, including granular, rod-shaped, and spiral rods,\nwere synthesized and incorporated into epoxy resin coatings for analysis.\nVarious characterization techniques, including X-ray diffraction (XRD),\nX-ray photoelectron spectroscopy (XPS), field emission scanning electron\nmicroscopy (FESEM), Brunauer–Emmett–Teller (BET), Fourier\ntransform infrared spectroscopy (FT-IR), and vibrating-sample magnetometer\n(VSM) analysis, were utilized to examine the structures of polymer\nnanoparticles. The FESEM images displayed that the indigo carmine\nconcentration changes during micellar polymerization led to morphological\nchanges in the polymer nanoparticles. Furthermore, electrochemical\nassessment methods such as Tafel analysis and electrochemical impedance\nspectroscopy (EIS) verified a reduction in corrosion current and enhancement\nin resistance due to the transformation of polymer nanoparticles from\ngranular to spiral rods, leading to 99.99% corrosion inhibition. The\ncorrosion rate of polymer nanoparticles varies significantly with\ntheir structure, exhibiting a rate of 1.9 × 10<sup>–6</sup> for granular forms, 4.08 × 10<sup>–7</sup> for rod-shaped\nstructures, and 3.45 × 10<sup>–10</sup> for spiral rods.\nIn the next step, the self-healing properties of the scratched coating\nloaded by the spiral rod polymer nanoparticles were investigated by\nFESEM, UV–vis microscope images, energy-dispersive X-ray spectroscopy\n(EDX), EIS, and Tafel tests. The ability of polypyrrole and indigo\ncarmine to inhibit corrosion, physically adhere to the metal surface,\nand create iron-indigo carmine complexes allows for the creation of\na protective coating on carbon steel surfaces.