Mechanical Behavior of Hierarchically-structured Polymer Composites

As the engineering of hierachically-structured polymer composites advances, so does the need for understanding the evolution of damage in these materials and their mechanical behavior. In natural systems, such as nacre, it is now well-understood that the damage accumulates across multiple length scales due to the nanoscale elastic biopolymers that bind together microscale aragonite crystals in a layered structure. The result is an extremely damage-tolerant microstructure that has a high hardness and fracture toughness. While it is difficult to duplicate this structure in synthetic polymer composites, it is still possible to alter mechanical behavior through structuring the material across multiple length scales. In this paper, the mechanical behavior of a hierarchically-structured polymer composite is studied by dispersing CNFs in a model epoxy system using sonication during solvent processing. A new nanomechanical characterization approach was used to characterize the multi-scale mechanical behavior in order to develop a model that was capable of determining the degree of dispersion and dispersion limit of CNFs that give rise to the hierarchical structure.