Molecular Dynamics Simulations of Graphene/Polyethylene and Its Tensile Properties

Molecular dynamics simulations have been used to study the micro structures and properties of graphene/polyethylene composite, and tensile properties of the composite have also been analyzed using a uniaxial tension simulation. The results show that, different from the pure polyethylene model, multi adsorption layers are formed by polyethylene molecules on the graphene surface due to equilibrium structure of the composite model. These adsorption layers are dynamic stable, through which the polyethylene molecules can migrate during the simulation progress. "Adsorption curing" occurs in the adsorption layers, where the polyethylene molecules become more extended and ordered, and their movements are inhibited in the direction perpendicular to the graphene surface. Tension simulation suggests improvement in tensile properties of the polyethylene matrix brought by graphene. In elastic region and yield region, the graphene can inhibit compression deformation in directions perpendicular to the strain, which keeps the stability of "adsorption curing" structures and causes sharp increase of stress in the composite model before yield strain. In softening region, the graphene bends greatly in one of the perpendicular directions and the "adsorption curing" structures are damaged, which results in stress decrease after the yield strain. The strain increase leads to not only change of non-bond interactions in the first two regions but change of intramolecular bonding energy in the last region for the composite system. The yield stress of composite increases with the increase of strain rate, which, however, has no effects on the general trend of the stress-strain curves for the model.