Interfacial Optimization And Dimensional Control Of Graphene

Nature is miraculous in developing strong, tough biomaterials, such as bone, nacre and spider silk. Recent studies have concluded that,1) hierarchical structures at micro-and nanoscale,2) sacrificial bonds and hidden lengths at the inorganic-organic interfaces, and 3) intrinsic/extrinsic toughening mechanisms (e.g., crack deflection/ twist) are three major reasons for the exceptional mechanical properties of biomaterials. Meanwhile, graphene is one of the strongest materials known so far and has been used to improve the mechanical properties of a variety of polymers. Since strength and toughness are commonly two contradictory properties in polymer nanocomposites, the addition of stiff fillers (e.g. graphene) frequently results in enhanced stiffness but reduced toughness and ductility. Up to now, how to balance the strength and toughness of materials still remains a huge challenge for materials scientists.In the present study, we demonstrate the importance of biomimetic principles for developing strong, tough polymer elastomers with high ductility and also exhibit the potential of graphene as a reinforcing filler of polymer elastomers with high ductility. By exploiting covalently and non-covalently functionalized graphene, sacrificial bonds and hidden length can be introduced at the interface of graphene-polyurethane. Our results reveal that the attached oligomer chains chemically identical to polyurethane can improve the dispersion of graphene in the matrix. While the covalent linkage of oligomer chains to graphene can enhance the efficiency of load transfer at the interface, the non-covalent interactions between pyrene groups and graphene can afford some mobility of graphene in the matrix and dissipate additional energy upon loading. Therefore, both rupture of the π-π interaction (sacrificial bonds) and release of the hidden length (dissociation of H-bonds between the polyurethane oligomer and polymer chains) enable the composite to exhibit high toughness and ductility nearly identical to the neat polyurethane (strain at break> 900%). We further achieve 50.7%, 104.8% and 47.3% increases in tensile strength, Young’s modulus and fracture toughness with a small amount (2.0 wt%) of functionalized graphene.On the other hand, the extraordinary properties of graphene nanosheets are highly dependent on their sizes. However, it is still a major challenge to control the lateral dimension of graphene with desired structure and performance for future composite applications. We here demonstrate a simple approach to prepare single-layer graphene nanosheets with a yield of> 90% by one-step hydrothermal treatment of graphene oxide. The addition of poly (vinyl pyrrolidone) is critical for producing single-layer graphene with specific sheet sizes and prevents the possible aggregation of graphene during hydrothermal reduction. Using hydrothermal treatment under different conditions, the lateral dimensions of the single-layer graphene nanosheets can be tuned to yield specific surface areas over a range of～3.5 orders of magnitude, from 30 to 9×10-3 μm2. We propose that hydrothermal cutting is initiated from the epoxy pairs in the central plane, and further advanced by reaction between H2O molecules and reactive sp3 carbon atoms at the edge or near defect domains, and/or by the strain induced from twisting of graphene nanosheets.