If the plexiglass beads get under mechanical pressure, they turn red or purple. Photo: B. Beiermann, University of Illinois
Read aloud American researchers have made a material that discolors under strong tensile forces. Under the load, certain atomic bonds break, resulting in a color change of the plastic. If the material breaks, the entire component is red or purple discolored, the materials researchers have discovered to Douglas David from the University of Illinois in Urbana-Champaign. In the Plexiglass-related material, the applied mechanical strain energy activates the chemical reaction of the color change. This could be used to build sensors that indicate material loads, for example in aircraft. Researchers could also develop self-healing materials in which, after mechanical stress, a chemical reaction reverts the component back to baseline, the researchers report. The researchers cleverly put two substances together for their development: In the polymer threads of Plexiglas plastic, they inserted a molecule that normally discolors under the influence of light. In sunglasses, for example, such substances lead to darkening in sunlight. The inserted molecule consists of several rings that break up at certain points when light is incident or mechanical force is applied. With the tearing of the atomic compound at this predetermined breaking point, the entire plastic discolored from colorless to red. The plastic has built a strain sensor so to speak, explain the researchers.

If the tensile load continues to increase, the now red material breaks in half. The researchers now hope to be able to modify the plastic to such an extent that self-healing forces are applied when the tensile load decreases: The molecules collapse at their predetermined breaking points and stabilize the plastic.

The scientists are now considering which other chemical reactions they can initiate by mechanical deformation. However, they still have two major obstacles to overcome: light and heat also set these reactions in motion. The material could be used in parachute ropes and climbing ropes or incorporated into the coatings of bridges, where it signals a threatening overuse in color.

Douglas David (University of Illinois, Urbana-Champaign) et al .: Nature, Vol. 459, p. 68 ddp / science.de? Martin Schäfer advertisement

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