Chao Wang, associate professor of chemistry, has recently synthesized a new type of artificial polymer using coordination complexes that can self-heal at a wide range of temperatures, as well as after repeated compromises in the polymer’s integrity. Using this new type of polymer, Wang hopes to apply its unique chemical properties to electronics and even humans in the future.
Wang explained the motivation for studying autonomous and self-healing polymers, pointing out that “self-healing is a very common property in nature, right? Self-healing is a very important survival property for animals and humans”: He then hypothesized that this property, seemingly exclusive to living tissue, could be expressed in synthetic materials.
There are currently some materials that can self-heal in a similar way to Wang’s polymer — but not without some shortcomings. These other self-healing polymers have “embedded microcapsules inside of the polymer” that essentially release healing agents upon incurred damage to the overall polymer structure. But as Wang pointed out, these polymers can only be repaired once; after the healing agents in the microcapsules have been released, the localized area cannot be healed if additional damage occurs.
Unlike other self-healing polymers, this new type of polymer that Wang and his lab have created contains coordination complexes that display “dynamic bonds,” or chemical bonds that are reversible. Wang explained how coordination complexes are structures that have non-metals, like carbon and nitrogen, which are bonded to a metal ion, like iron, at the center. The crux of his self-healing polymer lies within these chemical bonds.
Normally, a coordination complex would entail a metal ion being covalently bonded to six nonmetals. This bond is normally strong and stable since formation of coordination complexes contains inherently stable chemical properties, such as a decrease in free energy. The difference with this polymer is that not all of the bonds are strong, where instead, there is a mixture of weak, medium and strong bonds. And as Wang revealed, this property allows for the reversibility and self-healing of this polymer, even at low temperatures where this process normally ceases.
Nevertheless, Wang says that there is still more testing to be done with his autonomous self-healing polymer, especially in different conditions, admitting, “How to make a self-healing polymer durable with water and moisture — that’s the key issue.” He further explained how his lab is currently studying the stability of self-healing materials, and whether these polymers maintain their integrity even with other forms of corrosion like oxidation. With regards to the practical medical and clinical applications of this polymer for artificial muscles, or for people with prosthetics, he said that, “For human application, it’s really a long way to go.”
Nevertheless, Wang is still optimistic in the capabilities of self-healing polymers, saying that in the future, “I would like these polymers to have a similar lifespan to our conventional plastics.” Wang is convinced that these self-healing polymers will change our everyday life, citing how even Apple and other technology companies are looking into self-healing for use in their electronics. Wang assured that “this self-healing concept will go to the market, and to everyday life gradually. That will definitely be the future.”