Graphene is one of the best materials in terms of mechanical strength and stiffness; yet in its porous form, also known as graphene aerogel, it can become lighter than air, a property for which graphene has been proposed as a substitute for relatively rare and expensive helium. However, what makes graphene so special — its atomic thickness — often turns into a limiting factor as many applications rely on bulk materials properties. Extending the mechanical properties of graphene into the three-dimensional world is not straightforward. Fusing graphene flakes together into a bulk, for example, may quickly result in partial or complete loss of desired properties. To address this issue, Qin et al. have conducted a computational study with the aim of finding the optimal 3D graphene architecture with mechanical properties similar to those found in atomically thin graphene (Sci. Adv. 3, 2375; 2017 ).

The process of gradual fusion of graphene flakes into a 3D assembly was reconstructed using a full atomic model. The resulting structures were built from graphene similar to that obtained via chemical vapour deposition growth. Because of the highly curved nature of graphene, the geometry of the resulting 3D assembly resembled a periodic gyroid. These modelled structures were then 3D-printed (pictured) and used to study the effect of scaling on the mechanical properties of graphene. Qin et al. found that the scaling laws are dominated by material architecture rather than the mechanics of graphene itself. Under optimized conditions, tensile strength can be one order of magnitude higher than that of steel. What's more, the simulations can predict the optimum aerogel density according to a specific mechanical requirement. The results of the study imply that optimally high mechanical strength and low total material usage for a graphene 3D aerogel can now be achieved in practice. However, the findings also suggest that these 3D structures made of curvy graphene flakes become too soft and weak with increasing density. Therefore, further optimization of the structural design is required for this lightweight material to regain the necessary strength to compete with state-of-the-art materials.

Credit: AAAS