Crumpling and creasing graphene makes some of the wonder material's properties even better, researchers have found.
Although crumpling the one-dimensional layer of carbon atoms is not as easy as crumpling a sheet of paper, a team from Brown University found that mastering this process could pave the way for creating better self-cleaning surfaces. The reason is that crumpled graphene appears much more water repellent than the smooth variety. Creased graphene also seems to have better electrochemical properties, opening new possibilities for its use in battery electrodes and fuel cells.
In an article published in the latest issue of the journal Advanced Materials, the team led by post-doctoral fellow Po-Yen Chen, describes the method for creating crinkled graphene. They relied on a type of polymer membrane that shrinks when heated. As the films shrink, the graphene on top compresses and crumples.
The method could be used repeatedly for multiple wrinkling: after the first application, the shrinking substrate is dissolved and the wrinkled graphene layer placed on a new substrate to shrink again.
The team experimented with various ways of crumpling and studied how it affects the properties of the wonder material. Over three generations of crumpling, they were able to reduce the graphene sheet to one fortieth of its original size.
"As you go deeper into the generations you tend to get larger wavelength structures with the original, smaller wavelength structure from earlier generations built into them," said Robert Hurt, a professor of engineering at Brown and one of the paper's corresponding authors.
When experimenting with the highly crumpled sheet of graphene, the researchers found that it has become extremely hydrophobic - virtually impossible to wet with water. As soon as a drop of water touched the surface, it immediately rolled off.
The crumpled graphene was also found to provide 400 per cent higher electrochemical current density over flat graphene sheets, paving the way for much more efficient batteries.
"You don't need a new material to do it," Chen said. "You just need to crumple the graphene."
The team believes that compressed graphene could also open new possibilities for manufacturing of stretchable electronics and wearable sensors.
The team now plans to experiment with crumpling other two-dimensional materials, hoping to see the same effect in the materials’ properties.
"There are many new two-dimensional nanomaterials that have interesting properties, not just graphene," Wong said. "So other materials or combinations of materials may also organise into interesting structures with unexpected functionalities."