Micromechanics modeling of the elastic moduli of rGO/ANF nanocomposites

Abstract

Energy storage materials that also provide structural integrity are needed to decrease the weight of electrically powered ground and air vehicles. Toward this end, structural supercapacitor electrodes consisting of aramid nanofiber (ANF) and reduced graphene oxide (rGO) were reported in our previous work. Surprisingly, the experimentally measured tensile moduli of these rGO/ANF nanocomposites were not bounded by the experimentally measured moduli of the ANF and rGO materials and were an order of magnitude lower than those of Kevlar fibers and graphene sheets. The purpose of the present work is to develop a micromechanics model for elastic moduli to support the development of rGO/ANF multifunctional composite electrodes. Both the ANF and the rGO are transversely isotropic, wavy and randomly oriented, and no traditional isotropic polymeric matrix is present. We are aware of no existing micromechanics model that is applicable to such a composite. The Mori–Tanaka model is used three times, to model the rGO and ANF separately, and then the rGO/ANF composite films. The model predictions of elastic moduli were compared with experimental results. Waviness was found to be the main factor controlling the effective composite moduli, due to the extreme anisotropy of the rGO. This implies that the effective elastic moduli of rGO/ANF composites can be considerably increased by developing processing methods that reduce waviness. The experimentally observed unbounded moduli were attributed to the relationship between waviness and the volume fraction of the ANF.