Graphene, already a plenty weird wondermaterial, has an unexpected new property that could one day play a role in space exploration: When hit with light, it propels forward. Huh!
Scientists accidentally stumbled across this discovery when studying graphene sponges, crumpled up versions of the single-atom thick sheets of carbon. As the team used a laser beam to cut the graphene sponge, the beam itself seemed to inch the sponge forward. So they set up some controlled experiments, which New Scientist describes below:
The team placed pieces of graphene sponge in a vacuum and shot them with lasers of different wavelength and intensity. They were able to push sponge pieces upwards by as much as 40 centimetres. They even got the graphene to move by focusing ordinary sunlight on it with a lens.
So what’s going on? One obvious theory would be something similar to the idea behind solar sails. Photons of light have momentum, and they transfer it to whatever they’re hitting. But with the graphene sponge, it seemed to be moving too much to be momentum alone.
Here’s how New Scientist explained the team’s alternative theory:
Instead, they think the graphene absorbs laser energy and builds up a charge of electrons. Eventually it can’t hold any more, and extra electrons are released, pushing the sponge in the opposite direction. Although it’s not clear why the electrons don’t fly off randomly, the team was able to confirm a current flowing away from the graphene as it was exposed to a laser, suggesting this hypothesis is correct.
To be clear, this is a bizarre observation about graphene that still needs to be confirmed by other scientists. And while graphene is great, it’s hard to make on a commercial scale. It’s easy and fun to dream up uses for graphene, but we’ll have to wait and see whether it lives up our imaginations.
Picture: An artist depiction of a solar sail, which graphene could make obsolete. NASA