pH-Sensitive Polydopamine-La (III) Complex Decorated on Carbon Nanofiber toward On-Demand Release Functioning of Epoxy Anti-Corrosion Coating

Abstract

The high aspect ratio and unique thermal and electrical characteristics of carbon nanofiber (CNF) made it an ideal physical barrier against the penetration of corrosive ions. However, the poor compatibility of the CNF with the polymer matrix and the lack of active corrosion inhibitors are the key limitations of this nanomaterial, resulting in short-term anti-corrosion resistance. An intelligent self-healing epoxy (EP) coating, including CNF modified with a polydopamine (PDA)-La³⁺ complex, was successfully fabricated to overcome these issues. Electrochemical impedance spectroscopy (EIS) evaluation implied that mild steel (MS) submerged in a 3.5 wt % NaCl solution containing the CNF-PDA-La extract had a total corrosion resistance (R_T) of 3107 Ω cm² after 24 h, which is much greater than the MS immersed in the blank solution (1378 Ω cm²). Furthermore, the potentiodynamic polarization analysis indicated a 50% reduction in the corrosion rate (CR) of the MS soaked in the solution containing released PDA and La³⁺ inhibitors compared to the blank solution. EIS and salt spray analysis were used to assess the self-healing capabilities of epoxy coatings incorporating modified CNFs. EIS assessment of scratched coatings revealed a 117% improvement in R_T of the CNF-PDA-La/EP coating compared to the Blank/EP after 10 h of immersion in the saline solution. This enhancement is due to the intelligent release of PDA and La³⁺ inhibitors at the scratch sites, which can mitigate MS corrosion by forming a PDA-Fe complex and the deposition of La(OH)₃ on the MS surface. The salt spray test results also exhibited the CNF-PDA-La/EP coating's superior anti-corrosion capabilities after 20 days. Hence, this research presents a logical approach for developing anti-corrosion coatings with improved nanofiller compatibility and self-healing characteristics.