Molecular insights into the effect of graphene packing on mechanical behaviors of graphene reinforced cis-1,4-polybutadiene polymer nanocomposites.

Through united-atom molecular dynamics simulations, we build a series of graphene (GP) reinforced cis-1,4-polybutadiene (cis-PB) models with two novel GP structures, intercalated and stacked GP structures, to investigate the effect of different GP packing patterns on the chain structure, chain dynamics, uniaxial tension and visco-elastic behaviors, and correlate the microscopic mechanism with macroscopic mechanical properties. Simulation results show that the interlayer polymer chains in the void of intercalated GPs are strongly confined, leading to higher bond orientation of polymer chains during the stretch process compared with monodisperse systems. And due to this restriction effect, intercalated systems exhibit higher tensile stress under large tensile strain. For stacked systems, the interaction within GP layers and the orientation of the whole stacked GP structure play dominant roles in mechanical and visco-elastic properties. Furthermore, from the results that stacked systems have higher tensile stress and intercalated systems exhibit a higher storage modulus, we can conclude that the GP-GP interaction makes greater contribution than the GP-PB interaction and the chain confinement effect to the tensile behavior, whereas the restriction and orientation of polymer chains become more crucial factors than the GP-GP interaction under shear conditions. This work may provide rational means to tune the mechanical and visco-elastic properties of GP reinforced polymer nanocomposites.