Self-healing coatings

Self-healing coatings developed by researchers at the University of Illinois can protect materials from the effects of environmental exposure.

Applications range from automotive paints and marine varnishes to the thick, rubbery coatings on patio furniture and park benches.

Paul Braun, a professor of materials science and engineering, said: 'Starting from our earlier work on self-healing materials, we have now created self-healing coatings that automatically repair themselves and prevent corrosion of the underlying substrate.'

To make the self-repairing coatings, the researchers first encapsulate a catalyst into spheres less than 100 microns in diameter.

They also encapsulate a healing agent into similarly sized microcapsules.

The microcapsules are then dispersed within the desired coating material and applied to the substrate.

Braun added: 'By encapsulating both the catalyst and the healing agent, we have created a dual capsule system that can be added to virtually any liquid coating material.'

When the coating is scratched, some of the capsules break open, spilling their contents into the damaged region.

The catalyst and healing agent react, repairing the damage within minutes or hours, depending upon environmental conditions.

The performance of the self-healing coating system was evaluated through corrosion testing of damaged and healed coated steel samples compared to control samples that contained no healing agents in the coating.

Reproducible damage was induced by scratching through the 100-micron-thick polymer coating and into the steel substrate using a razor blade.

The samples were then immersed in a salt solution and compared over time.

The control samples corroded within 24 hours and exhibited extensive rust formation, most prevalently within the groove of the scratched regions, but also extending across the substrate surface.

In dramatic contrast, the self-healing samples showed no visual evidence of corrosion even after 120 hours of exposure.

Braun said: 'Our dual capsule healing system offers a general approach to self-healing coatings that operates across a broad spectrum of coating chemistries.

'The microcapsule motif also provides a delivery mechanism for corrosion inhibitors, antimicrobial agents, and other functional chemicals.'

The work was funded by Northrop Grumman Ship Systems, the US Air Force Office of Scientific Research, and the Beckman Institute.