Polymers that change their appearance in response to mechanical forces can warn of damage developing in a material before the stress causes structural failure.

Researchers now report in ACS Central Science that they've developed a first-of-its-kind elastic polymer blend that displays white fluorescence when deformed and then goes dark after relaxing back to its original shape.

A general approach to create such stress-sensing polymers is to integrate sensor molecules that change their optical properties when activated by mechanical force.

In most previous types of these polymers, however, activation is irreversible because it breaks covalent bonds in the sensors.

To do this, they built upon their previous work, published last year, in which they reported a polyurethane containing stress-sensing rotaxane consisting of ring-shaped fluorescent molecules threaded on dumbbell-shaped molecules featuring quencher groups at their center.

In the relaxed polymer, the quenchers were near the fluorescent rings and prevented them from glowing under ultraviolet light.

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