Mechanical properties and fracture resistance of three-dimensional graphene/polymer composites

This work reports the development of three-dimensional (3D) graphene structures, such as graphene aerogels (GAs), graphene woven fabrics (GWFs) and graphene foams (GFs), as interconnected fillers for polymer composites in an effort to achieve excellent mechanical properties and fracture resistance. The 3D graphene structures are aimed at totally eliminating the issue of filler dispersion using a few rational assembly techniques, such as liquid crystal based self-assembly, unidirectional freeze casting and template-directed chemical vapor deposition (CVD). The resulting 3D graphene structures are infiltrated with liquid epoxy resins followed by the thermal curing to obtain the composites. The 3D graphene/epoxy composites show concurrently improved elastic modulus, strength and fracture toughness. While the enhancements in modulus and strength of the composites are rather moderate due to the difficulties in achieving strong interfacial bonds, remarkable improvements in fracture toughness by 100 % against solid epoxy are achieved. The aligned rGO sheets, porous graphene struts, interwoven hollow graphene tubes, and high-density graphene networks facilitate unique toughening mechanisms, such as crack deflection, crack tip blunting, crack pinning and bifurcation, leading to significant energy dissipation during crack propagation giving rise to exceptional fracture resistances. Compared to GAs assembled from GO solutions, GFs and GWFs made by templated-directed CVD generally show better reinforcing effects due to the high-quality, seamlessly interconnected graphene networks. In view of such excellent reinforcing and toughening effects, the 3D graphene can also serve as interleaves to strengthen and toughen the conventional fiber reinforced composites, contributing to enhanced interlaminar fracture toughness. The excellent mechanical properties and fracture resistances render 3D graphene/epoxy composites a serious contender for emerging multifunctional applications.