Orientating graphene flakes in nanocomposites using rotating magnetic field and orientation evolution modeling

The orientation of 2D flakes in nanocomposites is of great value in determining the properties of nanocomposites, but their controlling and modeling are more difficult than those of microscale fillers therefore still remain challenging. External magnetic fields have been previously used to control the orientation of 2D materials in composites, but they only aligns flakes axially (only one degree of freedom constrained) instead of to an in-plane orientation state. Moreover, the evolution of orientation distribution of 2D materials during the orientating process has still been understood only empirically and phenomenologically, while a thorough understanding is needed to direct future manufacturing of nanocomposites. Herein, we present a rotating magnetic field (RMF) to orientate pre-magnetized graphene nanoplatelets (GNPs) to achieve an in-plane orientation in nanocomposites and a dynamic orientation model is developed to describe and parameterize the orientation evolution of 2D flakes in nanocomposites. Mechanical properties of the magnetically controlled nanocomposites outperform those of uncontrolled ones, where the modulus of nanocomposites with high filler contents increased by ∼10%, the tensile strength and toughness increased by ∼50% and ∼250%, respectively. The theoretical model based on the probability density function starts from single flakes and follows through to cover a large number of flakes in nanocomposites. It is validated by the agreement with experimental results obtained using wide-angle X-ray scattering. The technique of using RMF and the orientation modeling are demonstrated to be powerful in controlling and understanding the orientation of 2D materials, which is crucial in improving the properties of their nanocomposites.