Stiffness Enhancement in Nacre-Inspired Nanocomposites due to Nanoconfinement

Layered assemblies of polymers and graphene derivatives employ nacre's tested strategy of intercalating soft organic layers with hard crystalline domains. These layered systems commonly display elastic properties that exceed simple mixture rule predictions, but the molecular origins of this phenomenon are not well understood. Here we address this issue by quantifying the elastic behavior of nanoconfined polymer layers on a model layered graphene-polymer nanocomposite. Using a novel, validated coarse-grained molecular dynamics simulation approach, here we clearly show that the elastic properties of layered nanocomposites cannot be described by volume fraction considerations alone and depend strongly on both interfacial energy and nanostructure. We quantify the relative importance of polymer nanoconfinement and interfacial energy on polymer structure and elasticity, and illustrate the validity of our model for two polymers with different intrinsic elastic properties. Our theoretical model culminates in phase diagrams that accurately predict the elastic response of nacre-inspired nanocomposites by accounting for all material design parameters. Our findings provide widely applicable prescriptive guidelines for utilizing nanoconfinement to improve the mechanical properties of layer-by-layer nanocomposites. Our findings also serve to explain why the elastic properties of organic layers in nacre exhibit multifold differences from the native and extracted states.