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Ionic conducting stretchy, transparent polymer heals mechanical damage autonomously

Self-healing feature stems from forces between ionic liquid and polar polymer chains, which drive cross-coupling

by Mitch Jacoby
January 2, 2017 | A version of this story appeared in Volume 95, Issue 1

By designing a polar polymer and treating it with an ionic liquid, researchers have prepared a transparent, highly stretchable ionic conductor with the ability to autonomously heal mechanical damage (Adv. Mater. 2016, DOI: 10.1002/adma.201605099). The material may lead to applications in electrically activated transparent actuators and artificial muscles and skin that can sense touch. Numerous research teams have demonstrated self-healing, stretchy materials and stretchable, transparent conductors. But combining all of those properties in a single material has remained challenging. A team led by Chao Wang of the University of California, Riverside, and the University of Colorado’s Christoph Keplinger has succeeded in making such a material by harnessing forces between charged moieties in a highly fluorinated imidazolium ionic liquid and polar segments of a custom-made stretchable, transparent polymer—poly(vinylidene fluoride-co-hexafluoropropylene). The forces drive polymer chain cross-linking, a self-healing mechanism. The team used a film of the material in an electrically activated artificial muscle device. Then they cut the film, left the pieces in contact with each other, and reactivated the device 24 hours later. The self-healed film showed some scarring but functioned as well as a pristine film.

This pair of photos shows that a polymer used in artificial muscle device self-heals after being cut.
Credit: Adv. Mater.
Twenty-four hours after being cut (left), a transparent ion-conducting polymer heals, albeit with scarring (right). This healed film (~1.5 cm in diameter) functions like a pristine film, stretching reversibly (20% larger, right) in an artificial muscle device.


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