Book Description

To protect aluminum alloys including AA2024-T3 from corrosion, dual-pH sensitive smart coatings have been developed based on the encapsulation of inhibitor-loaded micro/nano-carriers. Previously reported pH-responsive coatings could only respond to either a pH increase or decrease during the corrosion process but not to both. To address this issue, a polyelectrolyte coacervate made from polyethylenimine and polyacrylic acid was developed. The obtained polyelectrolyte coacervate was found to degrade in the presence of either acidic or alkaline pH conditions. For the proof of concept, SrCrO4 as a model inhibitor was enclosed within the polyelectrolyte coacervate, and its release profile at different pH conditions was monitored by UV-vis spectroscopy. The entrapped SrCrO4 was released from the polyelectrolyte coacervate at a faster rate at both pH 2.5 and 10 compared to pH 7, and the released SrCrO4 inhibits the corrosion of AA2024-T3. Therefore, the developed polyelectrolyte coacervate is dual-pH sensitive and can be used to create a dual-pH responsive release system for corrosion protection of AA2024-T3. Dual-pH sensitive microspheres containing the corrosion inhibitor Ce(NO3)3 were fabricated with the polyelectrolyte coacervate as the shell material. Traditional preparation methods such as the layer-by-layer technique are time-consuming and require additional templates during the preparation process, so a simple and template-free coaxial electrospray method was developed to create Ce(NO3)3-loaded microspheres. The as-fabricated Ce(NO3)3-loaded microspheres have a core-shell structure and can release inhibitors when pH shifts to both acidic and alkaline regions. After introducing such microspheres into a polyvinyl butyral coating, the resulting coating system can improve the corrosion resistance of AA2024-T3. A microsphere-based smart coating might have limited corrosion inhibition applications due to the discrete distribution of microspheres within the coating and a negative impact on the integrity of the coating matrix. Thus, to address this issue, nanofibers containing a corrosion inhibitor were also developed. The nanofibers were prepared by the coaxial electrospinning technique with the chitosan/polyacrylic acid polyelectrolyte coacervate and Ce(NO3)3 as shell and core materials, respectively. The rendered nanofibers are also dual-pH sensitive and capable of releasing Ce(NO3)3 at both low and high pH conditions. A smart coating with embedded nanofibers can provide corrosion protection to AA2024-T3, and the nanofibers do not have a detrimental effect on the barrier property of the coating matrix. Furthermore, the nanofibers can facilitate the migration of Ce(NO3)3, leading to a continuous release of corrosion inhibitors at the same damaged site for repeated self-healing performance.