January 15, 2016

Making the invisible visible: Color-changing indicators highlight microscopic damage

Illinois professor Nancy Sottos and postdoctoral researcher Wenle Li led a team that
developed color-changing indicators to highlight microscopic cracks in structural materials.
Photo by L. Brian Stauffer

(January 15, 2016)  Damage developing in a material can be difficult to see until something breaks or fails. A new polymer damage indication system automatically highlights areas that are cracked, scratched or stressed, allowing engineers to address problem areas before they become more problematic.

The early warning system would be particularly useful in applications like petroleum pipelines, air and space transport, and automobiles – applications where one part’s failure could have costly ramifications that are difficult to repair. Led by U. of I. materials science and engineering professor Nancy Sottos and aerospace engineering professor Scott White, the researchers published their work in the journal Advanced Materials.

When cracks form, microbeads embedded in the material break open
and cause a chemical reaction that highlights the damaged area.
Image courtesy of Nancy Sottos

“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,” Sottos said. “We developed a very simple but elegant material to autonomously indicate mechanical damage.” 

The coating, applied to a steel plate, brightly highlights a thin zigzag scratch.
Image courtesy of Nancy Sottos

The researchers embedded tiny microcapsules of a pH-sensitive dye in an epoxy resin. If the polymer forms cracks or suffers a scratch, stress or fracture, the capsules break open. The dye reacts with the epoxy, causing a dramatic color change from light yellow to a bright red – no additional chemicals or activators required.

journal reference >>