Researchers at the Adolphe Markle Institute (AMI) and Hokkaido University in Japan have developed a method to tailor the properties of stress-indicating molecules that can be integrated into polymers and signal damages or excessive mechanical loads with an optical signal.
The prevailing approach is based on specifically designed sensor molecules that contain weak chemical bonds that break when the applied mechanical force exceeds a certain threshold.
This effect can cause a colour change or other pre-defined responses, but a fundamental limitation of the approach is that the weak bonds can also break upon exposure to light or heat.
This lack of specificity reduces the practical usefulness of stress-indicating polymers, and normally makes the effect irreversible.
The research team has devised a new type of sensor molecule that can only be activated by mechanical force, and unlike in previous force-transducing molecules, no chemical bond breaking takes place.
Instead, the new sensor molecules consist of two parts that are mechanically interlocked.
This interconnection prevents the separation if the two parts, while still allowing them to be pushing together or pulled away from each other.
Professor Christoph Weder, Chair of Polymer Chemistry and Materials at AMI, said: “The design approach allows one to tailor the properties of such sensor molecules, as their behaviour is quite predictable. We chose to demonstrate this by tackling materials the display white fluorescence when stretched.”
“Mechanoresponsive white fluorescence is in general difficult to achieve. It requires the combination of three sensor molecules with pre-defined emission colours.”
“In addition, the sensor molecules also need to exhibit a similar response to mechanical stress to achieve on/off witching of white emission when they are blended.”
