Anticorrosion organic–inorganic hybrid films constructed on iron substrates using self-assembled polyacrylic acid as a functional bottom layer

Abstract

Polyacrylic acid (PAA)–metal complex-based hybrid films with favorable anticorrosion performance were constructed directly on iron substrates. Thus, a high affinity of PAA for oxidized iron surface and its strong complexation ability to metal ions were fully used. The self-assembled PAA layer was first prepared on iron substrates by self-assembled PAA polymer in alcohol–water mixed solution. Despite a relatively poor anticorrosion performance, the as-prepared self-assembled PAA layer could be used as a functional bottom layer to fabricate PAA–metal complex films because PAA can strongly complex metal ions. Here, organic PAA films were further functionalized by directly immersing PAA film-coated iron specimens in aqueous solutions containing Ce3+ or Zn2+ or both metal ions to allow the complexation reaction between PAA and metal ions to proceed spontaneously. The obtained PAA–M (M = Ce, Zn here) hybrid films could more strongly suppress the corrosion of iron substrates in NaCl corrosive solution than organic self-assembled PAA films. PAA–Zn films exhibited the strongest corrosion protection ability, as exemplified by the appearance of only one time constant related to resistance and capacitance of hybrid films in the impedance spectra. In the mixed solution of Ce3+ and Zn2+ ions, the presence of Ce3+ could significantly promote the combination of Zn2+ with PAA polymers. However, as-fabricated PAA–Ce–Zn hybrid films showed impedance behavior quite differently from that of PAA–Zn films. This study is helpful in designing and fabricating environmentally friendly organic–inorganic hybrid conversion coatings with excellent anticorrosion performance.