That's one giant leap for inanimate matter
Pance Naumov of New York University in Abu Dhabi noticed the power that light can have on crystals in 2010, when he saw crystals of green fluorescent protein bend to more than 90 degrees under weak illumination.
Now he and his colleagues have seen tiny crystals containing cobalt, chlorine and nitrate groups leaping too, under ultraviolet light – and examined the process in more detail.
"It's fascinating," Naumov says. "What really impressed me is the magnitude of the response.."
Artificial muscle
Besides hopping, some crystals rolled or flipped, whereas others split off fragments or broke into two equal pieces. Light that was bright, but not quite as intense as sunlight on a clear day, prompted motion in a fraction of a second, but crystals exposed to much dimmer light took up to 20 seconds to respond.
The jumping response seems to be down to the way light energy causes atoms in the crystal to rearrange themselves, leading to a build-up of strain that is then explosively released.
Naumov says that heat should reverse these atomic rearrangements. So by alternately applying light and heat, the jumping crystals might be used to open and close micro-scale fluid valves or to form flexing artificial muscles.
"It is especially interesting that the mechanical energy is provided by a reversible chemical change," says chemist Philip Coppens of the University of Buffalo in New York State, who was not involved in the work.
Journal reference: Angewandte Chemie, DOI: 10.1002/anie.201303757
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