Self-healing graphene holds promise for artificial skin in future robots

Graphene, which is, in simple terms, a sheet of pure carbon atoms and currently the world's strongest material, is one million times thinner than paper; so thin that it is actually considered two dimensional. Notwithstanding its hefty price, graphene has quickly become a comer among the most promising nanomaterials due to its unique properties and versatile prospective applications.

The paper by published in Open Physics refers to an extraordinary yet previously undocumented self-healing property of graphene's, which could lead to the development of flexible sensors that mimic the self-healing properties of human skin.

The largest organ in the human body, skin has been known for its fascinating self-healing properties -- but until now, emulating this phenomenon proved too much of a challenge as humanmade materials lack this ability. Due to unprecedented stretching or bending and incidental scratches, artificial skin used in robots is extremely susceptible to ruptures and fissures. The study offers a novel solution where a sub-nano sensor uses graphene to sense a crack as soon as it starts nucleation, and surprisingly, even after the crack has spread a certain distance. This technology could quickly become viable for use in the next generation of electronics.

"We wanted to observe the self-healing behavior of both pristine and defected single layer graphene and its application in sub-nano sensors for crack spotting by using molecular dynamic simulation." Says Dr. Swati Ghosh Acharyya, the main author of the article. She continues: "We were able to document the self-healing of cracks in graphene without the presence of any external stimulus and at room temperature." The results revealed that self-healing occurred by spontaneous recombination of the dangling bonds whenever within the limit of critical crack opening displacement.

The researchers subjected single layer graphene containing various defects like pre-existing vacancies and differently oriented pre-existing cracks to uniaxial tensile loading till fracture. Interestingly enough, once the load was relaxed, the graphene started to heal and the self-healing continued irrespective of the nature of pre-existing defects in the graphene sheet. No matter what length of the crack, they all healed, provided the critical crack opening distance lied within 0.3 -- 0.5 nm for both the pristine sheet as well as for the sheet with pre-existing defects.

Simulating self-healing in artificial skin will open the way to a variety of daily life applications ranging from sensors, through to mobile devices and ultracapacitors.