Wonderful Engineering

Scientists Have Created A Polymer That Self-Destructs On Exposure To Sun

Department of Defense or the CIA will be closely observing the American Chemical Society (ACS) Fall 2019 National Meeting & Exposition since a team is presenting a self-destructing polymer at it.

Paul Kohl, Ph.D. from Georgia Tech, whose team has developed the self-destructing polymer, said, ‘This is not the kind of thing that slowly degrades over a year, like the biodegradable plastics that consumers might be familiar with. This polymer disappears in an instant when you push a button to trigger an internal mechanism or the sun hits it.’

The polymers have been particularly developed for the DoD. It makes sense that it is interested in electronic sensors and delivery vehicles that would be capable of literally leaving no trace. Such a material could really give new meaning to secret missions. The defining technique for the self-destructing polymer is known as ceiling temperature. Ceiling temperature is then linked to another concept known as ‘steric strain’ – a kind of repulsion of electrons.

If a ceiling temperature remains under a certain threshold, the steric strain remains stable. However, if the ceiling temperature crosses the threshold, the steric strain goes above to the point where the electrons end up repulsing so much that the material dissolves. You can observe this phenomenon in everyday life as well. Take the example of polystyrene – hard and solid plastic used for food packaging. It has a stable ceiling temperature but when you expose the material to fire, the material stars dissolving. The dissolution of polystyrene is actually thousands of chemical bonds breaking but in the case of self-destructing polymer created by Kohl’s team; only one chemical bond link has to be broken and the rest follow in a domino effect.

This is not the first attempt at making a self-destructing polymer but it is the first successful one. The biggest challenge in the past has been to keep such a material stable at room temperature. Kohl says, ‘Initially, we made it photosensitive to just ultraviolet light so we could make the parts in a well-lit room with fluorescent lighting, and it was just fine; it was stable.’ He says that when the material was exposed to sunlight, it would revert back to liquid form or vaporize. A vehicle that would have moved in the wee hours of the morning would disappear along with the dawn.

He also said, ‘’We have polymers designed for applications in which you come in the room, you turn the light on, and the thing disappears.’ The team has also been able to set time limits for depolymerization. Kohl explains, ‘We have a way to delay the depolymerization for a specific amount of time—one hour, two hours, three hours. You would keep it in the dark until you were going to use it, but then you would deploy it during the day, and you would have three hours before it decomposes.’