Multifunctionality and Control of the Crumpling and Unfolding of Large-Area Graphene

Abstract

Crumpled graphene films are broadly used, for instance in electronics ¹ , energy storage ^{2, 3} , composites ^{4, 5} , and biomedicine ⁶ . Although it is known that the degree of crumpling affects graphene's properties and the performance of graphene-based devices and materials ^{3, 5, 7} , the controlled folding and unfolding of crumpled graphene films has not been demonstrated. Here we report an approach to reversibly control the crumpling and unfolding of large-area graphene sheets. We show with experiments, atomistic simulations and theory that, by harnessing the mechanical instabilities of graphene adhered on a biaxially pre-stretched polymer substrate and by controlling the relaxation of the pre-strains in a particular order, graphene films can be crumpled into tailored self-organized hierarchical structures that mimic superhydrophobic leaves. The approach enables us to fabricate large-area conductive coatings and electrodes showing superhydrophobicity, high transparency, and tunable wettability and transmittance. We also demonstrate that crumpled graphene-polymer laminates can be used as artificial-muscle actuators.