This color-changing polymer warns of tiny damage you can't see

The material houses microscopic color-changing capsules that turn red for cracks and damage invisible to the human eye.

Tiny cracks can actually be a big deal when they're forming inside parts of your car or, say, a metal shell that's flying into space. University of Illinois research, led by Professors Nancy Sottos and Scott White, has lead to a polymer coating that could be an important early warning system, making it easier to find trouble spots before something really bad happens. When cracks form in the polymer, micro-beads also crack open, causing a chemical reaction that visibly highlights the damage with color. The capsules are pH sensitive, meaning any damage will cause a strong color change, from yellow to red, with no additional chemicals needed. Deeper, more serious, scratches and damage will create stronger hues of red as more capsules break open.

As Professor Sottos puts it: "Polymers are susceptible to damage in the form of small cracks that are often difficult to detect. Even at small scales, crack damage can significantly compromise the integrity and functionality of polymer materials."

It works on multiple kinds of polymers that can coat metals, other polymers and glass. Importantly there's no sign of degradation: the capsules will stay intact until actual cracks or damage happen. And compared to other techniques, it's not too expensive, either, given the high investment needed for space vehicles. "A polymer needs only to be 5 percent microcapsules to exhibit excellent damage indication ability," Sottos said. "It is cost effective to acquire this self-reporting ability." The researchers are now looking to pair this damage signaling with self-healing systems, meaning future materials could not only notify engineers of damage, but also attempt to repair themselves.