Title: Atomic insights into synergistic effect of 3D graphene nanoplatelet and carbon nanotube hybrids on the mechanical properties of polymer nanocomposites

Abstract

The unique three-dimensional (3D) hybrid structures of graphene nanoplatelet (GNP) and carbon nanotube (CNT) hybrid filler can improve dispersion and enhance interfacial properties to achieve excellent reinforced polymer composites. Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes (CNTs) on the mechanical properties of polyethylene (PE) nanocomposites. In order to reveal the synergistic effect of the morphology and arrangement of pillared graphene in enhancing the mechanical properties of polymer nanocomposites, the pillared graphene/PE (PG/PE) model were engineered. Moreover, by constructing the pillared graphene model and CNTs/graphene model, the effect of the structure, arrangement and dispersion of hybrid fillers on the tensile mechanical properties of PE nanocomposites was studied. The results show that the pillared graphene/PE nanocomposites exhibit higher Young’s modulus, tensile strength and elongation at break than non-covalent connected CNTs/graphene/PE nanocomposites. The tensile strength, Young's modulus and elongation at break of the pillared graphene/PE composites all increase first and then decrease as the length of the carbon nanotube increases. The multi-layer pillared graphene/PE composites have a higher Young's modulus than the single-layer pillared graphene/PE composites. Compared with CNTs/graphene hybrid, pillared graphene delivers a more significant synergistic effect and this is attributed to the self-supporting mechanism of pillared graphene. The pull-out simulations show that pillared graphene by CNTs has both large interfacial load and long displacement due to the mixed modes of shear separation and normal separation. Additionally, pillared graphene can not only inhibit agglomeration but also form a compact effective thickness (stiff layer), consistent with the adsorption behavior and improved interfacial energy between pillared graphene and PE matrix.