Adhesion-Diffusional-Based Corrosion Protection Mechanisms of Polyaniline-Primed Fluoropolymer Coatings

Abstract

In this study, we developed a series of dual-coating systems composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and electrodeposited polyaniline (PANI) as the primary coating and primer, respectively, for stainless steel (SS). Prior to the PVDF-HFP topcoat application, PANI (in either a doped emeraldine salt (ES) or dedoped base (EB) form) was electrodeposited potentiodynamically on either an etched or unetched SS substrate using H 2 C 2 O 4 as the supporting electrolyte. Tape tests showed improved PVDF-HFP adhesion on EB-PANI-primed substrates than on ES-primed samples. Impedance analysis and potentiodynamic chemistry were used to quantitatively investigate the electrochemical behavior and corrosion kinetics of the coated samples, respectively, in a 3.5 wt % NaCl corrosive solution. Electrochemical results revealed that the PVDF-HFP/EB-PANI dual-coating system exhibited superior corrosion resistance (low-frequency impedance modulus, |Z| 0.1Hz ∼ 10 6 Ω cm 2 ) compared to either the dual PVDF-HFP/ES-PANI or pristine PVDF-HFP coating (|Z| 0.1Hz ∼ 10 4 Ω cm 2 ). Based on the correlation between electrochemical data and water uptake, high water diffusivity for ES-PANI-primed PVDF-HFP coating (diffusivity, D ∼ 10.0 × 10 −10 mm 2 s −1 ) was obtained due to the ionic solvation of counterions, while relatively lower diffusivity for the EB-PANI-primed counterpart (D ∼ 5.0 × 10 −10 mm 2 s −1 ) was observed due to the effective impingement of water ingress by the insulating hydrophobic EB-PANI undercoat. Overall, we investigated the impact of the electronic state of an electroconductive polymer primer on the corrosion resistance of a two-coat system with a fluoropolymer topcoat and explored nuanced effects on adhesion and electrolyte diffusion, providing comprehensive insights and laying the foundation for tailored design strategies to enhance corrosion resistance, filling a critical gap in the current understanding and guiding future research in coating science innovation.

Superhydrophobic, Highly Adhesive, and Corrosion-Protective Fluoropolymer-Modified Polythiophene Coatings

“…However, when both silane pretreatment and top coating with fluoropolymer were employed (i.e., 5PH/PTH/SS mod ), the impedance increased to almost ∼7.2 MΩ cm 2 , indicating a synergistic effect that significantly boosts the corrosion resistance of the coated substrate. In our previous work employing PANI as an electroconductive primer to PVDF–HFP, we achieved a | Z | 0.1 Hz of approximately 1 MΩ cm 2 (coating thickness about 13 μm) . This result is comparable to our current findings, which also reached roughly the same magnitude using PTH as the electroconductive layer.…”

“…The chemical composition of a surface also primarily influences its surface energy. ,, For instance, Zisman et al demonstrated that the surface energy decreases with increasing fluorine content in a polymer, following the sequence: CH 2 > CH 3 > CF 2 > CF 3 . , Fluoropolymers exemplify this principle such that the presence of highly polarized and inert C–F bonds promotes material stability and offers a multifaceted defense mechanism against environmental degradation. − This attribute renders them invaluable for designing insulating layers that promote ionic permeability and prevent electron transfer between the metal and corrosive medium, thereby averting the oxidation process. − Polyvinylidene fluoride (PVDF) and its CF 3 -containing copolymer, PVDF- co -hexafluoropropylene (PVDF–HFP), represent two exemplary fluoropolymers extensively employed in the coating manufacturing industry. Renowned for their exceptional inertness, these polymers offer remarkable corrosion and wear resistance, alongside mechanical integrity, film-forming characteristics, low surface energy, and thermal stability. , The synergy between PVDF’s durability and chemical resistance and HFP’s inclusion promoting ease of processability yields coatings that boast mechanical flexibility, outstanding protective properties, and lower surface energy. , Despite their inherently low surface energy, these fluoropolymers alone cannot achieve superhydrophobicity. , Customizing rough surfaces using materials with low surface energy or generating a rough surface on hydrophobic materials is typically employed to achieve superhydrophobicity.…”

Two-Dimensional Zinc Silicate/Polyaniline Nanocomposites Enhance the Anticorrosion Properties of Epoxy Resin Coatings

“…When external potential changes or the material faces corrosion attacks, the stored charges can quickly move to the area that needs protection, forming an electrochemical protective layer that effectively blocks the invasion of corrosive media. This protective layer can not only buffer the attack of corrosive media but also suppress the progress of corrosion reactions by regulating the potential of the metal surface, thus forming effective protection for the metal substrate. − Chen et al successfully synthesized pentadecafluorooctanoic acid/polyaniline (PFOA/PANI) composite, creating hydrophobic coatings and improving the anticorrosion performance of epoxy resins. Dong et al successfully synthesized PANI with microcapsule structures and loaded MBT as a corrosion inhibitor, providing dual corrosion protection for carbon steel.…”