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Researchers in Japan are developing a self-healing polymer that can protect metals from corrosion and restore the substrate to its passive state.
The key to the coating is an intrinsically conducting polymer film (ICP) called polypyrrole, which could be used as an alternative to toxic chromates, Damian Kowalski, Mikito Ueda and Toshiaki Ohtsuka of Hokkaido University report in Self-healing ion-permselective conducting polymer coating, recently published in the Journal of Materials Chemistry.
The project “demonstrates a new approach to self-healing polymers that have the ability to repair artificial defects and restore the passive state of an underlying metal substrate,” according to the article. The ICP, “with a well-designed function of doped ions, possesses specific permselective properties, restricting incorporation of aggressive chlorides from corrosive electrolyte.”
(ICPs are, in effect 'synthetic metals', capable of conducting electrical currents or ions, Jon Watson of Highlights in Chemical Science notes in summarizing the research.)
Heading Off Damage
The permselective membrane “controls the release of healing ions to the defect zone when artificial defects are formed, efficiently inhibiting corrosion of the underlying metal substrate,” the researchers explain. The ions also react with the steel to form an insoluble iron molybdate salt in the defect zone.
This stops the healing ions from reacting with the metal before the coating is damaged, significantly increasing the lifetime of the coating, Kowalski said.
Paul Braun, an expert in self-healing coatings at the University of Illinois, notes that Kowalski's system is “much thinner than other coatings, which will be a distinct advantage for some applications,” Watson reports.
The researchers will turn next to further reducing the size and improving the healing response, the report says.
The full article is available here.
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