Understanding and modulating the conformation of graphene are pivotal in designing graphene macroscopic materials. Here, we revealed the sheet collapsing behavior of graphene oxide (GO) sheets by poor solvents in an analogy with linear macromolecules. Triggered by poor solvents, extended GO sheets in good solvents can collapse to hierarchically wrinkled conformations. The collapsing behavior of GO enabled the fabrication of amorphous self-standing GO and graphene papers with rich hierarchical wrinkles and folds over mutliple size scales. The collapsed GO and graphene papers had a rubber-like mechanical behavior with viscoelasticity. By our collapsing method, GO and graphene self-standing papers were designed to be stiff with high modulus or to become soft with low modulus of 100 MPa at a remarkably large breakage elongation up to 23%. Our philosophy of treating graphene as a 2D polymer enables the efficient control of molecular conformations of graphene and other 2D polymers and the design of macroscopic materials of 2D nanomaterials as in the polymer industry.
Keywords: graphene paper; rubber-like; sheet collapsing; viscoelasticity; wrinkles.