Modelling of folded graphene and related systems

Abstract

Graphene, a quasi-planar monolayer of sp2 -bonded carbon atoms known for its exceptional physical properties, is highly amenable to out-of-plane deformation. Recent studies have revealed that the creation of folded, pleated-like domains imparts novel characteristics to this material whilst permitting some of its existing properties to be effectively controlled through straining action via regulation of the emergent folding parameters. Despite the considerable influence that strain can have on the material properties of folded graphene, the literature pertaining to the nano-mechanical unfolding of folded, graphene-type systems remains scarce. In this work, molecular dynamics simulations were performed on three novel forms of folded graphene using an ad hoc protocol executable within LAMMPS to study their mechanical response to uniaxial tensile deformation. Patterned line defects were shown to constrain multiply folded graphene to a quasi-periodic, highly ordered morphology that gave rise to instances of pronounced negative tangent modulus – coincidentally with each fold opening – upon the application of uniaxial stress. The severe lack of periodicity observed in the corresponding profiles of the pristine folded systems was attributed to the absence of defect lines which permitted folds to be more mobile and at times merge, effectively reducing the frequency of fold openings. These structural differences were explained, for the first time, via a macroscale model based on the mechanics of paper folding. Overall, this study attests to the potential for defect-type fold lines to guide the unfolding process of folded graphene, and provides valuable insight into the different mechanisms involved in the unfolding of specific forms of folded graphene.