Effect of flake size on the mechanical properties of graphene aerogels prepared by freeze casting

Aerogels enable a wide range of potential applications owing to their ultralow density, superelasticity, high specific surface area, energy-absorbability and so on. However, it is usually difficult to precisely control their mechanical performance, which largely hinders their applications. Here, we prepared anisotropic graphene aerogels assembled with flakes having different sizes ranging from sub-micron to similar to 80 mu m by the freeze casting technique, using ice as a template to assembling graphene oxide (GO) sheets into 3-dimensional (3D) aerogels. We found that graphene flake size has a profound effect on the mechanical performance of the assembled graphene aerogels, particularly their strength, modulus and fatigue resistance under compression. Larger flakes had stronger interaction when assembled, which made them more resistant to slipping between adjacent flakes during deformation. As a result, the graphene aerogel with larger flake size showed both higher strength and fatigue resistance. Our research provides a new way of controlling the mechanical properties of graphene aerogel by only adjusting the intrinsic properties of the flakes, e.g., size, without crosslinking agent or co-assembly with other materials as in previous studies.