“What we've done is to realize the wish of translating these 2D materials into three-dimensional structures”Markus Buehler
While in in 2D form graphene is believed to be the strongest known material, it has not been straightforward to translate this property into feasible 3D materials. However, researchers at MIT have managed to develop a porous 3D form of graphene with a strength 10 times that of steel while also being a great deal lighter. To achieve this, they compressed and fused tiny flakes of graphene using heat and pressure to produce a material with a strong, stable structure, a sponge-like configuration and a density of only 5%.
In the study, which was published in the journal Science Advances [Qin et al. Sci. Adv. (2017) DOI: 10.1126/sciadv.1601536], the team developed a range of 3D models to analyze the material’s behavior down to the individual atoms, helping them to design a mathematical framework that closely matches experimental observations.
The concept is similar to a sheet of paper, which has little in the way of strength when flat, and is easily crumpled; however, when made into certain shapes, such as rolled into a tube, it can offer much greater strength along its length and support significant weight. In the same way, when graphene flakes are arranged geometrically and then treated, they can produce forms with an extremely strong configuration. These configurations were tested for their tensile and compressive properties, while their mechanical response under loading was simulated with models.
Although 2D dimensional materials are very strong and offer unique electrical properties, due to their thinness they are not practical for making useful 3D materials. As project leader Markus Buehler pointed out, “What we've done is to realize the wish of translating these 2D materials into three-dimensional structures”. The team showed that the key characteristic of these 3D forms involves their geometrical configuration rather than anything to do with the actual material, indicating that the graphene material or other strong and light materials, such as polymers or metals, could be produced based on similar geometric features.
As the shape has numerous tiny pores, such materials could also be used in filtration systems for water or chemical processing. However, the results from the atomistic computational modeling proved that one hoped-for approach was not viable, that of designing 3D graphene structures so light they could replace the helium in balloons. Tests demonstrated that at such low densities, the material did not have enough strength and such balloons would collapse due to air pressure.