Stimuli-responsive nanocapsules, which can respond to various environmental stimuli and release their encapsulated payload on demand, have attracted wide interest in different fields in recent years. In this work, a novel kind of polypyrrole (PPy) nanocapsules is fabricated and loaded with zinc salt corrosion inhibitors. The synthesized PPy nanocapsules respond to two different external stimuli (pH- and redox-responsive) and can control the release of their encapsulated corrosion inhibitors. The nanocapsules can detect the micro-environmental pH or surface-potential changes associated with the corrosion initiation of the metal substrate. When introduced into a protective epoxy coating, the fabricated PPy nanocapsules inhibit the anodic and cathodic corrosion reactions. The superior corrosion resistance and active corrosion protection effects of the epoxy-PPy-Zn coatings are further demonstrated via electrochemical and long-term immersion tests. The low-frequency impedance, coating resistance, and oxide film resistance increase after about 400 h of exposure in a 3.5 wt % NaCl solution, reflecting the enhanced corrosion protection properties and excellent repairing performance of the coating. Furthermore, the epoxy-PPy-Zn coating can avoid the pitting corrosion of 304 stainless steel. Overall, we have fabricated double stimuli-responsive PPy nanocapsules via a simple and effective strategy and incorporated them into a corrosion-resistant epoxy coating for protecting Fe-based metal substrates.
Keywords: active corrosion protection; coatings; conducting polymers; double stimuli-responsive nanocapsules; stainless steels.