A major emerging field of materials science is to formulate new materials which, like living organisms, can self heal from macroscopic or microscopic damage.  An international team of researchers has created a new kind of coating that could form the basis of true self-healing car paints [press release 1; press release 2; video].  

Nissan implemented a primitive form of self-healing car paint in its EX and G lines, but the actual real world results of that endeavor have been mixed.

This new effort is comprised of teams from Case Western Reserve University in Cleveland, Ohio, led by Stuart J. Rowan; the Adolphe Merkle Institute of the University of Fribourg in Switzerland, led by Christoph Weder; and the U.S. Army Research Laboratory at Aberdeen Proving Ground in Maryland, led by Rick Beyer.

They have created a new self-healing coating that could be used as the basis of paint.  The coating is formed via a technique called supramolecular assembly.  Whereas usual polymers are single large molecules with thousands of atoms, the special new coating is an ionic polymer composed of metal ions and smaller polymeric molecules.  The metal ions act as ”glue", linking the smaller molecules together to form chains.

The polymer's special character shows up when you expose it to UV light.  The polymer enters a "molten" state, filling gaps and scratches.  It then resolidifies.  

Stuart Rowan, a professor of macromolecular engineering and science and director of the Institute for Advanced Materials at Case Western Reserve University, describes, "These polymers have a Napoleon Complex.  In reality they're pretty small but are designed to behave like they're big by taking advantage of specific weak molecular interactions."

Researchers created large scratches and dings on the test coat, then shined a UV light on it, locally.  The material "healed" itself in seconds.  And unlike the self-healing found in living creatures, the material exhibited the ability to go through numerous scratching/healing cycles in a brief time without a loss of integrity.

The researchers evaluated a number of metal ion polymers before picking their current target.  They found that mechanical properties (strength, flexibility without breaking, etc.) increased as the order of the resulting polymer increased.  But as the mechanical strength increased, the ability to be healed decreased.  So scientists opted for a moderate polymer with decent healing and mechanical traits.

As we discussed in our previous piece on self-healing plastics, microcracks -- microscopic scratches or cracks -- ultimately lead to big damage over time.  Aside from resisting macroscopic scratches, the materials could undergo periodic treatments with the UV lamp to prevent wear from microcracks as well.

The research team feels the coating is ready for prime time.  Professor Rowan says the next step is commercialization, stating, "One of our next steps is to use the concepts we have shown here to design a coating that would be more applicable in an industrial setting."

The study on the work was published [abstract] in the journal Nature, perhaps science's most prestigious journal.  

The work was funded by the Army Research Office of the U.S. Army Research Laboratory, the U.S. National Science Foundation, and the Adolphe Merkle Foundation.