AsianScientist (Feb. 24, 2020) – A research group in Japan has created a stress-detecting ‘smart’ polymer that shines brighter when stretched. Their findings, published in Chemical Communications, could be used to track the wear and tear on materials used in engineering and construction industries.
By the time cracks or other visible defects appear in construction materials, the structural integrity of a building may already be compromised. In the present study, researchers led by Dr. Ayumu Karimata at the Okinawa Institute of Science and Technology Graduate University (OIST), Japan, have created a copper-containing polymer that lights up proportionately to the amount of mechanical force exerted on it, paving the way for early detection of mechanical strain.
The scientists created their polymer by incorporating copper complexes—structures formed by linking copper atoms to carbon-containing molecules—with polybutylacrylate. The copper complexes, which hold the polybutylacrylate chains together, naturally glow when exposed to ultraviolet light, a property known as photoluminescence.
When the polymer is stretched, the copper complexes emit light at a greater intensity, leading to a brighter glow. The copper complexes therefore act as mechanophores—compounds which undergo a change when triggered by a mechanical force.
Most mechanophores are made from organic compounds which change color or emit light when mechanical stress breaks a weak chemical bond. However, Karimata noted that a relatively large force is required to break the chemical bond, so the mechanophore is not sensitive to small amounts of stress.
“Also, the process of breaking the bond is often irreversible, so these stress sensors can only be used once,” he said.
In contrast, the new copper mechanophores are sensitive to much smaller stresses and can respond quickly and reversibly. The scientists reported that their polymer film immediately brightened and dimmed in response to being stretched and released.
Karimata proposes that the acrylic polymer could eventually be adapted to create a stress-sensing acrylic paint for coating different structures, such as bridges or the frames of cars and aircraft.
“As we can see even from the direct visualization of the polymer, stress is applied across a material in a non-uniform way,” said Karimata. “A stress-sensing paint would allow hotspots of stress on a material to be detected and could help prevent a structure from failing.”
The article can be found at: Karimata et al. (2020) Highly Sensitive Mechano-controlled Luminescence in Polymer Films Modified by Dynamic Cui-based Cross-linkers.
Source: Okinawa Institute of Science and Technology Graduate University.
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