Viscoelastic Properties of Wrinkled Graphene Reinforced Polymer Nanocomposites – Effect of Interlayer Sliding Among Graphene Sheets

The effect of wrinkles formed in multilayer graphene sheets (MLGS) on the viscoelastic properties of polymer nanocomposites has been largely unknown. Building upon the developed coarse-grained models of MLGS and PMMA coupled with molecular dynamics simulations, we have systematically investigated wrinkled MLGS reinforced PMMA nanocomposites with different numbers of graphene layers and different configurations of the wrinkles. We find that with an increasing level of wrinkling, the modulus and yield strength of the nanocomposites decrease. The reinforcement effect also becomes more significant with increasing number of graphene sheets. Interestingly, the enhancement of modulus and yield strength is not embodied under the out-of-plane shear. However, we observe a sudden stress drop during shear deformation of specific wrinkled MLGS reinforced nanocomposites. We find that these specific nanocomposites also show peculiarly large loss tangent, indicating an increasing level of energy dissipation. It is attributed to the activation of the interlayer sliding among MLGS. Our study demonstrates for the first time that the viscoelastic properties of polymer nanocomposites can be tuned through wrinkle engineering of MLGS.