Conducting polymer composite coatings for corrosion protection

Due to unique electrical conductivity and redox properties of conducting polymers, they have been explored for active corrosion protection of metals, exploiting redox phenomena to enable the self-healing of polymer coatings. While self-sealing has been extensively studied, proving the effect of redox action has been a challenge. We have combined electrochemical techniques and in-situ atomic force microscopy (AFM) to study corrosion protection mechanism of carbon steel with polymer composite coatings containing polyaniline (PANI). The results revealed reversible oxidation and reduction of PANI with a corresponding volume change in the coating. As an example, the corrosion protection mechanism of a solvent-borne alkyd coating containing 1 wt.% PANI on carbon steel in 3 wt.% NaCl solution was investigated by cyclic voltammetry (CV) and electrochemical AFM measurements under different applied potentials. The CV curves (Figure 1) and electrochemical AFM images (Figure 2) demonstrated a reversible conversion between the oxidized emeraldine salt and reduced leuco-emeraldine base of PANI.

OCP and electrochemical impedance spectroscopy measurements during long-term exposure gave rise to an enhanced stability of corrosion protection by the composite coating, which can be attributed to redox conversion and self-healing effect of the PANI.