Defect-tolerant nanocomposites through bio-inspired stiffness modulation

A biologically inspired, multilayer laminate structural design is deployed into nanocomposite films of graphene oxide-poly(methyl methacrylate) (GO-PMMA). The resulting multilayer GO-PMMA films show greatly enhanced mechanical properties compared to pure-graphene-oxide films, with up to 100% increases in stiffness and strength when optimized. Notably, a new morphology is observed at fracture surfaces: whereas pure-graphene-oxide films show clean fracture surfaces consistent with crack initiation and propagation perpendicular to the applied tensile load, the GO-PMMA multilayer laminates show terracing consistent with crack stopping and deflection mechanisms. As a consequence, these macroscopic GO-PMMA films become defect-tolerant and can maintain their tensile strengths as their sample volumes increase. Linear elastic fracture analysis supports these observations by showing that the stiffness modulation introduced by including PMMA layers within a graphene oxide film can act to shield or deflect cracks, thereby delaying failure and allowing the material to access more of its inherent strength. Together, these data clearly demonstrate that desirable defect-tolerant traits of structural biomaterials can indeed be incorporated into graphene- oxide-based nanocomposites.