Soft electronic materials have potential applications in human–machine interfaces, wearable devices, and underwater exploration. Yet for now, those materials require dry environments. Polymer-based artificial skin swells and loses maneuverability and conductivity when exposed to water, because hydrogen bonds form between the polymer chains and water molecules.
Now Chao Wang, Benjamin Tee, and coworkers have developed a soft, ionically conductive artificial skin that can autonomously self-heal in both dry and wet conditions. Inspired by the bodies of jellyfish, the transparent material, named GLASSES, combines an amorphous polar fluoroelastomer with a hydrophobic fluorine-rich ionic liquid. Both components consist mostly of carbon–fluorine bonds, which are very poor hydrogen bond acceptors. As a result, the material does not interact with water molecules, and it retains its properties underwater even after 12 hours.
The researchers demonstrated that the material can repeatedly self-heal (see figure); it can maintain nearly all its toughness, stress, and strain even after 10 cuts with a ceramic knife. The healing process is entropy driven; slight contact between the cut pieces allows the polymer chains to slowly diffuse into one another. And unlike polymers composed of metal particles, GLASSES remains transparent when exposed to water. The researchers used the material to create sensors for pressure and strain and successfully wrapped it onto circuit board.
The distinctive mechanical, optical, and electronic properties of GLASSES could lead to its application as an artificial skin for underwater soft robots that monitor sea creatures. Such robots would be durable enough for long-term studies and could even lure organisms with optical signals. (Y. Cao et al., Nat. Electronics 2, 75, 2019.)
