A team of engineers at Duke University, Durham, NC, are layering atom-thick lattices of carbon with polymers to create unique materials with a broad range of applications, including artificial muscles. Because of its unique optical, electrical, and mechanical properties, graphene is used in electronics, energy storage, composite materials and biomedicine. But, it is difficult to handle because it has a tendency to “crumple,” which makes it difficult to control.
To manipulate the graphene, the engineers attached it to a rubber film pre-stretched many times its original size. When the pre-stretched rubber film was relaxed, part of the graphene detached from the rubber while other part kept adhered, forming an attached-detached pattern. As the rubber was relaxed, the detached graphene crumpled. But, when the film was stretched again, the adhered graphene pull on the crumpled portion and unfolded it.
In addition, the engineers layered the graphene with different polymer films to make a “soft” material that can act like muscle tissues by contracting and expanding on demand. When electricity is applied to the graphene, the artificial muscle expands in area; when the electricity is cut off, it relaxes. Varying the voltage controls the degree of contraction and relaxation, giving actuation strains over 100 percent.
