Stealth glider made out of special polymer self-destructs in sunlight

https://www.newscientist.com/article/2214248-stealth-glider-made-out-of-special-polymer-self-destructs-in-sunlight/

Glider in the sky

Gliders like this could one day self-destruct

blickwinkel/DuM Sheldon/Alamy

Spies and soldiers might soon be able to go behind enemy lines using a parachute or glider made from a polymer that vanishes on exposure to sunlight.

“This started off with building small sensors for the government — microphones, cameras, things that detect metal,” says Paul Kohl at the Georgia Institute of Technology, who presented the work at a meeting of the American Chemical Society in California this week.

The idea was that these sensors could be spread across a battlefield, say, and used to collect information for the army. “But you don’t want anyone to discover it and take it apart and see how it works,” says Kohl.

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That’s why he and his team wanted to invent a self-destructing material. They began with polymers that have a low ceiling temperature, which is the point at which the key bonds holding the substance together begin to break.

Lots of polymers break down slowly when they reach this temperature because many bonds have to be broken. But Kohl designed his material so that as soon as one bond breaks the whole thing rapidly unzips.

They based their polymer on a chemical called an aldehyde and mixed in other chemical additives that can either make it rigid for use in a glider or sensor, or flexible to make a fabric for a parachute.

Sunlight or artificial light can trigger the material to go poof. Or, in true spy style, a small light emitting diode can be placed inside a device to trigger the self-destruct process on demand. All that’s left behind is a residue and a faint smell, which Kohl says are from the additives that control the rigidity of the material.

Gliding in the dark

Kohl says he and his team have already made a glider with a six-foot wingspan from the material. It can only carry objects weighing about 1 kilogram, so it could only be used to covertly transport objects, not people, for the moment. The glider would have to travel under cover of darkness to avoid disintegrating in flight.

Marek Urban at Clemson University in South Carolina says the chemical reactions involved in the depolymerisation are not novel, but this covert intelligence application may be.

But he says there may be a problem with the residue left behind after the polymer disappears. “My question is, does this system leave you with some monomers you didn’t start with? This could be extremely harmful because if you don’t know what those monomers are as a result, you could create another problem,” says Urban.

Kohl says he’s tested the residue on plants, which did experience some discoloration but did not die. “If you’re out in the wild and it’s rocky and certainly in a desert or things like that, there’s very little concern about leaving a lot of hazardous materials behind,” he says.

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