Optimization design on simultaneously strengthening and toughening graphene-based nacre-like materials through noncovalent interaction

Nacre exhibits outstanding mechanical properties due to its hierarchically microstructural features and associated multiscale deformation behaviors, enlightening human to design high-performance graphene-based nacre-like materials (GNMs) in the past decade. However, those GNMs mimicking brick-and-mortar microstructure always cannot give consideration to both strength and toughness because the pullout process of graphene oxide (GO) sheets that amplifies toughness in GNMs is extremely limited compared to natural nacre. Toward this end, a combination of modified shear-lag model and atomic simulations is proposed to investigate the optimal strategy of simultaneously strengthening and toughening for GNMs reinforced by strong noncovalent interfacial interactions. The modified shear-lag model can well couple the interlayer sliding and structural stability to characterize the toughening effect during the pullout process. We demonstrate that the interfacial toughness and shear strength tuned by interlayer noncovalent interactions significantly impact the effective tensile strength of GNMs, while toughness is mainly dominated by the interlayer sliding before strain localization during the pullout process of GO sheets. Melamine molecule is chosen as the representative interlayer crosslink agent owing to the ultrastrong noncovalent interaction between melamine and GO. Our atomic simulations indicate that melamine bound to GO by anomalous hydrogen bonding can greatly improve the interfacial shear stress and maintain the interlayer energy-dissipation efficiency resulting from the breaking and reforming of hydrogen bonds. An optimal range of melamine content and GO oxidation degree is then explored for synchronously superior strength and toughness by balancing the competitions among the reduction of intralayer tensile limit of GO sheets, the improvement of the interlayer shear strength, and the reduction of interfacial toughness. In particular, a scaling law is proposed as the evaluation criterion to correlate the inner inelastic deformation of GNMs and their mechanical properties, revealing why interlayer noncovalent interaction can optimize strength and toughness simultaneously while most other crosslinks usually cannot. (C) 2019 Elsevier Ltd. All rights reserved.