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.