Morphology-Dependent Corrosion Inhibition and Self-Healing Properties of Polypyrrole and Indigo Carmine Composites on Carbon Steel 1018 in a Saline Environment

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