Effect of lattice stacking orientation and local thickness variation on the mechanical behavior of few layer graphene oxide

Investigation of few layer 2D materials is fundamentally important to bridge the gap between monolayer and bulk properties, and practically meaningful for applications as reinforcement nanofillers and layered electronic devices. Few layer introduces differences from intrinsic properties of monolayers due to the complexity of structural heterogeneities, such as lattice stacking orientation and local thickness variation. In this work, few layer graphene oxide (GO) with different structural heterogeneities were studied using atomic force microscopy-based deflection measurements and transmission electron microscopy (TEM). Direct TEM evidence of fracture surfaces and molecular dynamics (MD) simulations revealed decoupled and dissimilar layer crack patterns for misaligned bilayer. In contrast, aligned bilayer GO generally fractured with a larger portion of common cracks shared by both layers, indicating stronger interlayer interaction. MD results also revealed insignificant effect of lattice alignment on the strength and toughness of GO bilayers. Scaling up even to similar to 5 layers and above revealed significant local thickness heterogeneity and consequently a similar to 60% reduction of the normalized fracture force and toughness. MD simulations on partially intercalated few layer GO revealed anisotropic and heterogeneous stress distributions, as well as stress concentration near the inner edges, which may account for the significant reduction of strength and toughness. (C) 2018 Elsevier Ltd. All rights reserved.