Scientists have developed a new self-healing material that conducts ions to generate current, and could one day help your broken smartphone to repair itself. Researchers created the stretchable and transparent polymeric material with an eye on electronics and soft robotics that can repair themselves.
“A self-healing material, when carved into two parts, can go back together like nothing has happened, just like our human skin,” said Chao Wang from University of California, Riverside in the US. “I have been researching making a self-healing lithium ion battery, so when you drop your cell phone, it could fix itself and last much longer,” said Wang.
The key to self-repair is in the chemical bonding. Two types of bonds exist in materials, Wang said. There are covalent bonds, which are strong and do not readily reform once broken; and noncovalent bonds, which are weaker and more dynamic. The hydrogen bonds that connect water molecules to one another are non-covalent, breaking and reforming constantly to give rise to the fluid properties of water.
“Most self-healing polymers form hydrogen bonds or metal-ligand coordination, but these are not suitable for ionic conductors,” Wang said. Wang’s team turned instead to a different type of non-covalent bond called an ion-dipole interaction, a force between charged ions and polar molecules.
“Ion-dipole interactions have never been used for designing a self-healing polymer, but it turns out that they are particularly suitable for ionic conductors,” Wang said. 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.