What do all smartphones have in common, regardless of price or manufacturer? Other than the ‘smart’ aspect, all may crack or even shatter to pieces if dropped. Even though some show more resilience than others, no existing smartphone is truly break proof. However, if a recently developed self-healing material is commercialized, this impediment may be defeated. In an article published in the journal Advanced Materials, scientists report the successful development of a self-healing polymeric material that could soon be used to manufacture self-repairing smartphones. The researchers presented their work at the 253rd National Meeting & Exposition of the American Chemical Society (ACS), held on April 4, 2017.
What Are Self-Healing Materials?
As the name suggests, self-healing materials have the ability to repair themselves when damaged, though the amount of damage and the conditions for self-healing might influence the healing capability. Human skin is, of course, one of the naturally occurring self-healing materials. Given normal conditions and adequate time, human skin can recover from blisters, cuts, etc. In the same way, scientists from different research groups have been working towards the development of synthetically-created self-healing materials for over a decade. Highly cited scientific articles are proof of the efforts put in this direction.
What Is the Idea?
Believe it or not, the inspiration for this self-healing material comes from Wolverine, a fictional character in the Marvel Universe. When Dr. Chao Wang (one of the leading researchers involved in this research) was young, he idolized Wolverine from X-men. The material his team developed surely had something in common with Wolverine: extended longevity via regenerative healing.
Dr. Wang wanted to develop a self-healing material which could go back to its original form when broken, just like human skin. Basically, his research goal was to make a self-healing lithium ion battery which could fix itself when a cell phone was dropped. This self-healing polymeric material is developed for electronics and soft robotics that could potentially self-repair. Since the material is stretchable, transparent and conducts ions to generate a current, it could help extend the life of smartphones.
How Is This Material Different?
The key to self-repair lies in the chemical bonding. Out of the two types of bonds in materials, covalent bonds are stronger and don’t readily repair once broken while non-covalent bonds are weaker and more dynamic. For example, 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 aren’t suitable for ionic conductors,” Wang said.
Thus, Wang’s team resorted to a different type of non-covalent bond called an ion-dipole interaction, a force between charged ions and polar molecules. According to Wang, ion-dipole interactions haven’t ever been used to design self-healing polymers, but it has become apparent that they’re especially suitable for ionic conductors. The central design concept in the development of the self-healing material is to use a polar, stretchable polymer, poly(vinylidene fluoride-co-hexafluoropropylene), along with 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.”, Wang explains.
These changes did make a significant difference and the resulting material could stretch up to 50 times its usual size. Moreover, the material automatically stitched itself back together completely within 24 hours after being torn in two.
When validated and commercialized, these self-healing materials can address multiple issues associated with mobile phones and electronics. The obvious advantage is the extended lifetime of the electronic device making it cost-effective in the long run. What’s more, this extension of an electronic device’s lifetime can ensure significantly less electronic waste and decrease the amount of toxic waste resulting from them. So, the Wolverine material is an innovation that is not only pocket-friendly but also environment-friendly. No wonder it’s a ‘Marvel’!
What’s Next?
After the encouraging results obtained with this self-healing material so far, the next step would be the improvement of material properties by polymer alteration for applications involving harsh conditions, such as high humidity. “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.” Wang said.
Image courtesy of pixabay.com
