Clasping folds enable superior elastic strength of graphene films

Abstract

Two-dimensional graphene sheets show strong potential for use in fabrication of macroscopic films, as they have exceptional mechanical properties owing to their in-plane strength1–6. Improvements in the stacking order of flat two-dimensional sheets have led to corresponding improvements in the strength and toughness of such films7–11. In addition, modulation of the spatial conformation of individual units has enabled the development of benchmark materials with superior properties12,13; however, this has remained elusive in the case of two-dimensional sheets. Here we report a strategy for preparation of graphene films with a combination of high strength (2.9 GPa), toughness (84.5 MJ m−3) and elastic strain (5%). We attribute these performance gains to a fold-clasping lamellar structure achieved by modular assembly of surface-folded multilayer graphene oxide flakes. We identify a pull-to-push transition of force chain topology and propose a shear-lock stress transfer strategy in the fold-clasping lamellar graphene film that enables advances in mechanical properties. This work demonstrates the modular design of spatial conformation of two-dimensional flakes on a large scale and further improves the performance of macroscopic films for potential applications in lightweight structural components. Two-dimensional graphene films with unusual folded surfaces are synthesized through a modular assembly strategy and show enhanced strength, toughness and elastic strain owing to stress distribution between interlayer folds.