Jack F. Douglas, Sinan Keten, Fernando Vargas-Lara, Wenjie Xia
We show by molecular dynamics simulation that bulk materials composed of graphene nanosheets exhibit fluid-like properties similar to linear polymer melts at elevated temperatures and that these materials transform into a glassy or foam state at low temperatures. Distinct from an isolated graphene sheet, which exhibits a relatively flat shape in solution, we find that graphene sheets in a melt state structurally adopt more crumpled configurations and a corresponding smaller average size, as normally found for ordinary polymers. Upon approaching the glass transition, these two-dimensional polymeric materials exhibit a slowing down of their dynamics that is likewise similar to ordinary linear polymer glass-forming liquids. Bulk graphene materials in their glassy foam state have an exceptionally large free-volume and high thermal stability because its glass-transition temperature (i.e., 𝑇𝑔≈1600 K) is relatively high in comparison to conventional polymer materials. Our findings suggest that graphene melts have interesting lubricating and plastic flow properties at elevated temperatures, and graphene foams appear to be highly promising as high surface filtration materials and fire suppression additives for improving the thermal conductivities and mechanical reinforcement of polymer materials.