Colour change

Force-sensitive polymers under development at the University of Illinois change colour when overstressed.

The polymers contain mechanically active molecules called mechanophores. When pulled with a certain force, specific chemical reactions are triggered in the mechanophores, leading to the change in colour.

In her previous work, Nancy Sottos, a Willett professor of materials science and engineering at the university, and one of the developers of the new polymer, showed that a mechanical force could be used to induce a reaction in mechanophore-linked polymers that were in solution.

Now, her research team has shown that it can perform a similar feat in a solid polymer.

To demonstrate the mechanochemical response, the researchers prepared two different mechanophore-linked polymers and subjected them to different levels of mechanical stress.

In one polymer – an elastomer – the material was stretched until it broke in two. A vivid colour change in the polymer occurred just before it snapped.