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Chameleon-like elastomers with molecularly encoded strain-adaptive stiffening and coloration

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Science  30 Mar 2018:
Vol. 359, Issue 6383, pp. 1509-1513
DOI: 10.1126/science.aar5308

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Active camouflage from a polymer

Human skin is soft and compliant, but it can quickly become stiff when deformed to prevent injury. Chameleon skin can change color when the animal goes from a relaxed to an excited state. Although these properties can be captured individually in synthetic materials, the combination of different dynamic responses can be hard to control. Vatankhah-Varnosfaderani et al. created triblock copolymers of the ABA variety, where the A blocks have a linear structure and the B blocks are like bottlebrushes. When strained, these polymers stiffened like human skin and changed color, thus giving the materials a range of adaptive properties.

Science, this issue p. 1509

Abstract

Active camouflage is widely recognized as a soft-tissue feature, and yet the ability to integrate adaptive coloration and tissuelike mechanical properties into synthetic materials remains elusive. We provide a solution to this problem by uniting these functions in moldable elastomers through the self-assembly of linear-bottlebrush-linear triblock copolymers. Microphase separation of the architecturally distinct blocks results in physically cross-linked networks that display vibrant color, extreme softness, and intense strain stiffening on par with that of skin tissue. Each of these functional properties is regulated by the structure of one macromolecule, without the need for chemical cross-linking or additives. These materials remain stable under conditions characteristic of internal bodily environments and under ambient conditions, neither swelling in bodily fluids nor drying when exposed to air.

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