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Color Changing Warning System May Prevent Costly Material Damage And Repair

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Materials degrade and get damaged overtime. Unfortunately, it is often difficult to detect these damages until the structure already breaks. By this time, repair may already be too difficult and even costly.

A new polymer damage indication system, however, can automatically highlight damaged areas that can compromise the integrity of a material.

By highlighting cracked, scratched and stressed areas, the system allows engineers to deal with the problematic areas before these get worse and become more problematic.

Nancy Sottos, from the University of Illinois Urbana-Champaign, who helped developed the warning system, said that polymers are susceptible to damages that come in forms of small cracks that can be difficult to detect.

She noted that even small-scale cracks can significantly compromise the functionality and integrity of polymer materials. The material they developed, however, can warn of such problems early on.

Sottos and colleagues embedded an epoxy resin with tiny microcapsules of PH-sensitive dye. Once the polymer gets cracks, scratches or fractures, the capsules break open setting of a reaction between the epoxy and dye that causes color change from light yellow to bright red.

Because more microcapsules are broken when the damage is deeper, the resulting color becomes more intense. This makes it possible to visually evaluate the extent of the damage.

"High resolution in situ autonomous visual indication of mechanical damage is achieved through a microcapsule-based polymeric material system," the researchers wrote in their study, which was published in the journal Advanced Materials on Jan. 11.

"Upon mechanical damage, ruptured microcapsules release a liquid indicator molecule."

The researchers found that the system worked for a range of polymer materials that can be applied to coat substrates, which include glasses, metals and polymers. The system also appeared to have long-term stability with no color fading and no leaking of microcapsules to generate false positives.

Such system can have useful applications in space transport, vehicles, and petroleum pipelines, where failure in one part may result in costly consequences that are difficult to repair.

"Detecting damage before significant corrosion or other problems can occur provides increased safety and reliability for coated structures and composites," said study researcher Scott White.

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