Photoluminescent polymer gets brighter under stress
The new polymer detailed in a the Chemical Communications journal under the title “Highly sensitive mechano-controlled luminescence in polymer films modified by dynamic CuI-based cross-linkers” consists of polybutylacrylate integrating copper complexes (where copper atoms are linked to organic molecules). The paper reports that the copper complexes are acting as a mechanophore within the polymer. When the polymer is
When the polymer is stretched (force = F), the mechanophore
glows brighter. Courtesy of OIST.
stretched under ultraviolet light, the copper complexes glow at a greater intensity than without the mechanical stress.
What the researchers observed, is that the copper complexes changed shape continuously, but as the complexes increased in size, they became less flexible and gave off a brighter glow. The team surmised that the larger, less flexible complexes were able to release light more efficiently because their motion was restricted, causing them to lose less energy than the smaller, more freely moving complexes. They then exploited this relationship between flexibility and brightness to create a stress-detecting polymer.
“When the copper complexes are incorporated into the polymer as cross-links, the act of stretching the polymer also reduces the flexibility of the molecules,” researcher Ayumu Karimata said. “This causes the copper complexes to luminesce more efficiently with greater intensity.”
incorporated as cross-linkers (left) and two vials of the
isolated copper complexes (right). The polymer films and
isolated copper complexes luminesce under ultraviolet light.
Courtesy of OIST.
The copper mechanophores developed by the OIST team are sensitive to smaller stresses than mechanophores made from organic compounds, which change colour or emit light when mechanical stress breaks a weak chemical bond.
“A relatively large force is required to break the chemical bond, so the mechanophore is not sensitive to small amounts of stress,” Karimata explains. “Also, the process of breaking the bond is often irreversible and so these stress sensors can only be used once.”
On the contrary, with copper-based mechanophores used as cross-linkers in polybutylacrylate, mechanical stress as low as 0.1MPa or small strain values under 50% can be detected via progressive changes in luminescence intensity.
The researchers want to adapt the acrylic polymer to create a stress-sensing acrylic paint that could be used to coat different structures, such as bridges or the frames of cars and aircraft.
“A stress-sensing paint would allow hot spots of stress on a material to be detected and could help prevent a structure from failing”, notes Karimata. The integrated copper-based mechanophores could also be used to measure the performance of synthetic polymers and track deterioration in materials that are used in engineering and construction.
Okinawa Institute of Science and Technology Graduate University – www.oist.jp
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
