Apr 5 2017
Image Credits: Sergey Peterman/shutterstock.com
Researchers report that the Marvel Universe has inspired them in a way that has led them to develop a self-healing polymeric material, with an eye toward electronics and soft robotics that can repair themselves. Stretchable and transparent, the material conducts ions to generate current and it is a possibility that it could eventually help your broken smartphone go back together again.
Today, at the 253rd National Meeting & Exposition of the American Chemical Society (ACS), the researchers will present their findings. ACS, the world’s largest scientific society, is holding the meeting here through Thursday. More than 14,000 presentations on a plethora of scientific topics will be featured.
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.
Chao Wang, Ph.D., University of California, Riverside
"Chemical bonding is the key to self-repair. In materials there are two types of bonds that exist; covalent and non-covalent bonds," Wang explains. Covalent bonds, which are strong and don’t readily reform once broken. Then there are non-covalent bonds, these are weaker and more dynamic. For example, the hydrogen bonds connecting water molecules to one another are non-covalent, breaking and reforming constantly which is why water has fluid properties.
Most self-healing polymers form hydrogen bonds or metal-ligand coordination, but these aren’t suitable for ionic conductors.
Chao Wang, Ph.D., University of California, Riverside
Wang’s team turned to ion-dipole interaction, a force between charged ions and polar molecules. This type of interaction is a different type of non-covalent bond. “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 says. The key design idea in the material's development was to use a polar, stretchable polymer, poly(vinylidene fluoride-co-hexafluoropropylene) and a mobile, ionic salt. Ion-dipole interactions between the polar groups in the polymer and the ionic salt link the polymer chains together.
As a result the material could stretch up to 50 times its usual size. After being torn in two, within a day, the material automatically stitched itself back together.
The team generated an “artificial muscle” by placing a non-conductive membrane between two layers of the ionic conductor, as a test. The new material responded to electrical signals, bringing motion to these artificial muscles. They are called artificial muscles because biological muscles move in response to electrical signals in a similar fashion (though Wang’s materials are not intended for medical applications).
The team will next focus it's attention to working on improving the material’s properties by altering the polymer. For example, they are testing the material in high humidity and similar harsh conditions.
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.
Chao Wang, Ph.D., University of California, Riverside
Wang acknowledges funding from start-up funds from the University of California, Riverside.