Conductive polymer can make ‘self-healing’ smart phones

Researchers in the United States have developed a self-healing polymeric material for electronics and soft robotics that can auto-repair. The material is stretchable and transparent, conducts ions to generate current and make self-repairing phones.

Chao Wang, lead researcher, said: "When I was young, my idol was Wolverine from the X-Men. He could save the world, but only because he could heal himself. A self-healing material, when carved into two parts, can go back together like nothing has happened, just like our human skin. I've been researching making a self-healing lithium ion battery, so when you drop your cell phone, it could fix itself and last much longer."

Wang's team at the University of California, Riverside, turned instead to a different type of non-covalent bond called an ion-dipole interaction, a force between charged ions and polar molecules.

The key to self-repair is in the chemical bonding. Wang said: “Most self-healing polymers form hydrogen bonds or metal-ligand coordination, but these aren't suitable for ionic conductors.”

“Ion-dipole interactions have never been used for designing a self-healing polymer, but it turns out that they're particularly suitable for ionic conductors.”

The key design idea in the development of the material was to use a polar, stretchable polymer, poly/vinylidene fluoride-co-hexafluoropropylene, plus a mobile, ionic salt. The polymer chains are linked to each other by ion-dipole interactions between the polar groups in the polymer and the ionic salt.

The resulting material could stretch up to 50 times its usual size. After being torn in two, the material automatically stitched itself back together completely within one day.

As a test, the researchers generated an ‘artificial muscle’ by placing a non-conductive membrane between two layers of the ionic conductor. The new material responded to electrical signals, bringing motion to these artificial muscles, so named because biological muscles similarly move in response to electrical signals.

For the next step, the researchers are working on altering the polymer to improve the material's properties. They are testing the material in harsh conditions, such as high humidity.

Wang added: “Previous self-healing polymers haven't worked well in high humidity. Water gets in there and messes things up. It can change the mechanical properties. We are currently tweaking the covalent bonds within the polymer itself to get these materials ready for real-world applications."