Issue Date: December 19, 2011
Polymer Chemistry: Self-Healing Materials
Search all the scientific literature of the 20th century for “self-healing materials” and you’ll come up with just a handful of results. But expand the search by a decade into the 21st century and suddenly there are hundreds of hits.
Chalk that up to Scott R. White, a materials engineering professor at the University of Illinois, Urbana-Champaign. When White and his colleagues published the paper “Autonomic Healing of Polymer Composites” in Nature in 2001, they sparked a research effort that would grow to include hundreds of researchers globally and spawn three international meetings. In 2010 alone, more than 100 papers on self-healing materials were published, White says.
“Not in my wildest dreams did I imagine the field would take off like this,” White tells C&EN. “It’s been really exciting to see the growth of this entirely new field.”
In that 2001 paper, White and coworkers reported how they loaded an epoxy with microcapsules containing dicyclopentadiene. Also dispersed throughout the epoxy was a ruthenium carbene Grubbs catalyst that mediates ring-opening metathesis reactions. Wherever the epoxy was cracked or otherwise damaged, the microcapsules would burst open and expose their dicyclopentadiene payload to the catalyst, which would polymerize the diolefin and heal the crack.
“What we set out to do was to demonstrate truly autonomous self-healing, where the crack was the only stimulus for the healing reaction to occur,” explains Nancy R. Sottos, a materials science professor at Illinois who was part of the research effort.
Since then, scientists have expanded on the type of materials they can make self-healing, including structural composites, adhesives, coatings, flexible polymers, ceramics, metal, and concrete. And they have also come up with different chemical reactions that can be used to heal cracks.
White founded Autonomic Materials Inc. (AMI) in 2005 to commercialize self-healing materials. The company is poised to launch its first product: an additive made of self-healing capsules that goes into the powder coatings used to prevent metal corrosion. The material can be used on just about anything that’s large, made of steel, and is expensive to take out of commission for repairs, says Magnus Andersson, AMI’s vice president of business development. It could be used on ships, pipelines, bridges, and construction equipment, he notes.
As for what’s next, Sottos says, “We’ve been wondering if it’s possible to not just heal, but to regenerate material,” in the same way that the body regenerates its bones.
“Bone is this great material that remodels,” White adds. “It’s constantly laying down new material and absorbing old material.” Is it possible, he wonders, to make engineered structures that do the same thing?
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