Polymeric material designed for self-healing smartphones and soft robotics

Self-healing materials are no longer something that we just see in a sci-fi film. Researchers are working towards developing a self-healing polymeric material to enable electronics and soft robotics to can repair themselves.

A new material not only heals itself, but it also stretches up to 50 times its usual size; these properties could fix your phone’s battery if it cracks or prevent it from breaking in the first place. Photo courtesy of Wang lab

The key to this stretchable, transparent self-healing materials is in the chemical boning. A University of California team explored different kinds of bonds and discovered that non-covalent bonds called an ion-dipole interaction—a force between charged ions and polar molecules—could be used to enable the “self-healing” mechanism of the material.

“Most self-healing polymers form hydrogen bonds or metal-ligand coordination, but these aren’t suitable for ionic conductors,” says Chao Wang, Ph.D.

“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,” Wang exlains.

The team designed the material using 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. This enables the resulting material to stretch up to 50 times its size. And after being torn in two pieces, the material automatically stitched itself back together completely in one day.

Wang and the team tested the material by generating an “artificial muscle” by placing a non-conductive membrane between two layers of the ionic conductor. The material responded to electrical signals, bringing motion to the artificial muscle.

The team is taking their research one step further by altering the polymer to improve its properties.

“Previous self-healing polymers haven’t worked well in high humidity,” Wang says. “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.”

Once fully vetted, the applications for this material are endless. The team hopes that it could possibly be used in smartphones to regenerate and put themselves back together when dropped.

“When I was young, my idol was Wolverine from the X-Men,” Chao Wang, Ph.D., says. “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.”

The research was presented at a meeting of the American Chemical Society.

www.acs.org