Interlayer crosslinking to conquer the stress relaxation of graphene laminated materials†
For any structural material, mechanical relaxation is a vital factor to determine its capability to bear dynamic loading. Macroscopically assembled graphene materials (MAGMs) have emerged as promising carbonaceous materials with high mechanical strength for potential structural uses. Considerable effort has been initially focused on the promotion of mechanical strength, most of it static. However, dynamic mechanical behaviour has long been ignored. Here, we observed a severe relaxation behaviour of macroscopically assembled graphene papers with laminated structures caused by the viscoelastic nature of the interlayer interactions. We found that the relaxation behaviour of laminated structures of two-dimensional graphene conforms to a ternary Maxwell–Wiechert model. The relaxation was considerably relieved by enhanced interlayer crosslinking to retard interlayer slippage. With the enhancements of crosslinking strength and increasing density, permanent stress was promoted to 84.1%, significantly higher than 14.7% for graphene oxide papers and 43.2% for the original reduced graphene papers. Analogous to chemically crosslinked polymeric rubbers, we used this interlayer crosslinking method to relieve the mechanical relaxation and improve the stretching elasticity of graphene laminated materials at a large strain of 10%. Our work reveals an ignored relaxation behaviour of MAGMs and develops an efficient interlayer crosslinking strategy to conquer stress relaxation, enabling the modulation of structures and properties under general guidance and paving the way for their realistic applications as structural materials.