PORTLAND, Ore.--Graphene is expected to replace silicon as the a faster, lighter and lower power material to build chips with as silicon approaches the end of the International Technology Roadmap for Semiconductors (ITRS). Now Duke University researchers claim that graphene can also be made into an electro-mechanical material suitable for applications ranging from energy harvesting and optical switching to artificial muscles for robots.
Graphene's electrical properties are well known, but so far researcher have been unable to harness them for electro-mechanical applications because of uncontrollable damage that often occurs during deformation, leaving it permanently crumpled. But Duke researchers now claim to have solved the crumpling problem.
"Graphene is extremely thin and difficult to unfold once it is deformed," said Xuanhe Zhao, a professor at Duke. "But we have developed a method that solves this problem, allowing the folding and unfolding of large-area graphene films."
The key, according to Zhao, is layering a pre-stretched rubber film between layers of graphene, such that when the composite is relaxed, the graphene folds into neat accordion-like nanoscale structures that can be flattened back out.
"The folding and unfolding of these graphene sheets can be controlled by simply stretching and relaxing the electro-active polymer to which it is attached," said Zhao.
Graphene crumples into the structure shown here, but can be flattened back out by applying a voltage, enabling an electro-mechanical-optical material suitable for energy harvesting, optical switching and artificial muscles for robots. Source:Duke University
Zhao and his associates are currently working on three applications: creating artificial muscles by stimulating the electroactive-polymer; using the process in reverse to harvest energy from its deformation: as well as harnessing the composite material's optical properties as a switch--since it is transparent when flat but opaque when folded up.
Zhao is also working to fine tune the folding and unfolding process with post doctoral fellow Jianfeng Zang and doctoral candidates Qiming Wang and Qing Tu at Duke, along with professors Markus Buehler and researcher Seunghwa Ryu at MIT and professor Nicola Pugno at the Universita di Trento (Italy), who performed the nanoscale validation of the underlying mechanism enabling the folding and unfolding process.
Funding for the project was provided by the National Science Foundation's Triangle Materials Research Science and Engineering Center, NSF Materials and Surface Engineering program, and National Institute of Health.