Article

Self-healing material comes of age

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by Journal Of Commerce

Self-healing materials or material coatings have barely intruded into our thoughts, yet a decade of research is yielding results that are sure, eventually, to grab our attention.
Self-healing material comes of age

Column

Korky Koroluk

Self-healing materials or material coatings have barely intruded into our thoughts, yet a decade of research is yielding results that are sure, eventually, to grab our attention.

All involve nanotechnology, the science and technology of the control of matter on an atomic and molecular scale. Some folks call it the science of the super-small.

Among the early nanotech products that are either on or very close to the market, are new protective coatings developed at the University of Illinois that can, without external intervention, heal themselves when scratched.

The self-healing elements are enclosed in microcapsules that tear open when the coating is scratched.

The system is made up of two kinds of microcapsules, one filled with polymer building blocks, the other with a catalyst. The microcapsules can be mixed into a wide range of coating. When the microcapsules are ripped open, their contents flow into the scratch and combine to form a caulk-like seal.

To test the system, researchers coated steel plates with a coating containing the microcapsules, and other plates with a conventional coating.

The plates were then scratched and immersed in salt water for five days. The plates painted with the new coating were protected against rust, while those with conventional coating showed significant rusting.

The researchers believe the coating would work well on ships, oil rigs, pipelines, bridges, anywhere metals are exposed to harsh environments and where frequent repainting is costly.

Self-healing technology is taking a different form in crash barriers and guardrails.

For those uses, researchers in the United States have developed a new type of polyurethane that absorbs shocks, then rebounds into its original shape.

Most polyurethanes might rebound to about 95 per cent of their original shape after one impact, somewhat less than that after a second impact, and so on, until they simply don’t rebound.

Or, some may rebound too quickly, which could cause a crashed car to bounce back into lanes of traffic. That’s why materials scientists had to develop the new polyurethane.

The new barriers are now in use at some auto race tracks and are being evaluated in the U.S. for use in places like bridge abutments and along concrete barriers that separate lanes of traffic.

A research team in Germany has been working on another problem: how to create microcapsules filled with healing compounds that could be infiltrated into protective metal coatings applied to other metals.

The idea is that when the metal coating is punctured or scratched, the capsules in the damaged area burst and ooze restorative compound liquids called trivalent chromates, which react with nearby metal atoms to form tough, protective films just a few molecules thick to repair the damage.

The problem was not making the capsules, but stabilizing them during the electroplating process, where they tended to stick together in the liquid electrolytes.

Specially developed detergents added to the mix fixed the problem.

The German researchers now have proved their techniques in electroplated layers of copper, nickel and zinc, and are confident that self-repairing materials based upon their work should be commonly available in a few years.

They are also investigating other applications for the technology and believe that lubricants such as silicone oils can be added to the capsules to lubricate the surfaces of damaged ball bearings.

None of this is available yet from your building-supplies dealer, but the advent of nanotechnology means that products like these — and many others — will inevitably make their way into the builders’ world.

Korky Koroluk is a regular freelance contributor to the Journal of Commerce. Send comments or questions to editor@journalofcommerce.com

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