Graphene Size and Morphology: Peculiar Effects on Damping Properties of Polymer Nanocomposites

Nanomaterials with their extremely high free surfaces can effectively augment damping in nanocomposites via frictional sliding along the interface of nanomaterials and a matrix. Despite this potential, existing state of knowledge about the damping behavior of graphene reinforced nanocomposites is at an embryonic stage. In particular, it is not clear how various morphological parameters of graphene contribute to damping. We aim to reveal the mechanical damping behavior of graphene-reinforced polymer nanocomposites as a function of the surface morphology of graphene nanoplatelets through combined experiments and continuum modeling. The vibrational damping behavior of graphene nanocomposites was studied via dynamic mechanical analysis via cycling tension-compression tests. Two graphene types, single-layer graphene (SLG) and graphene nanoplatelets (GNP), with different aspect ratios in polystyrene (PS) matrix were used. We developed a micromechanical model which relates damping in nanocomposites to filler-matrix frictional sliding. The experimental work demonstrated that the addition of GNP will increase the damping properties of the nanocomposites by up to similar to 70%. The model predictions for PS-GNP were in good agreement with experimental data. However, contrary to the model predictions, the damping coefficient of nanocomposites with lower aspect ratio particles (PS-SLG) was lower than PS-GNP. Further experimental studies showed that the surface roughness of the SLG (owed to their small thickness) has a negative effect on damping properties as they delay interfacial debonding and frictional sliding. Flat (less rough) graphene triggers intrinsic friction mechanism earlier and may be more beneficial to enhance damping. Surface undulation of the nanoparticles, which can happen for atomically thin particles, will delay damping.