Crumpled graphene and rubber combined to form artificial muscle
Despite its numerous wondrous properties, a propensity to stick together and be difficult to flatten out once crumpled can make working with graphene difficult and limit its applications. Engineers at Duke University have now found that by attaching graphene to a stretchy polymer film, they are able to crumple and then unfold the material, resulting in a properties that lend it to a broader range of applications, including artificial muscles.
Before adhering the graphene to the rubber film, the researchers first pre-stretched the film to multiple times its original size. The graphene was then attached and, as the rubber film relaxed, the graphene layer compressed and crumpled. This caused part of the graphene to detach from the rubber layer and resulted in an attached-detached pattern measuring just a few nanometers in size. It was this pattern that allowed the graphene to "unfold" when the rubber layer was stretched out again.
“In this way, the crumpling and unfolding of large-area atomic-thick graphene can be controlled by simply stretching and relaxing a rubber film, even by hand,” said Xuanhe Zhao, an Assistant Professor at the Pratt School of Engineering.
The researchers say that by crumpling and stretching, it is possible to tune the graphene from being opaque to transparent. Furthermore, different polymer films can result in different properties. These include a "soft" material that acts like an artificial muscle. When electricity is applied, the material expands, and when the electricity is cut off, it contracts. The team was able to control the degree of contraction and relaxation by varying the voltage.
“New artificial muscles are enabling diverse technologies ranging from robotics and drug delivery to energy harvesting and storage,” Zhao said. “In particular, they promise to greatly improve the quality of life for millions of disabled people by providing affordable devices such as lightweight prostheses and full-page Braille displays. The broad impact of new artificial muscles is potentially analogous to the impact of piezoelectric materials on the global society.”
Currently, artificial muscles in robots are mostly of the pneumatic variety, relying on pressurized air to function. However, few robots use them because they can't be controlled as precisely as electric motors. It's possible then, that future robots may use this new rubberized graphene and other carbon-based alternatives as a kind of muscle tissue that would more closely replicate their biological counterparts.
The team's study is published online in the journal Nature Materials.
Source: Duke University