Tunable mechanical properties of graphene by clustered line pattern hydroxyl functionalization via molecular dynamics simulations

The effects of clustered line patterns of hydroxyl functionalization and percent surface coverage along the armchair and zigzag directions of the graphene lattice on the mechanical response of graphene sheets (GS) under tension loading, in zigzag and armchair directions, and under shear loading in the zigzag direction were studied. The initial, functionalization induced bending deformation, caused by clustered line pattern arrangements, led to strong elastic anisotropy of graphene with an increased linear compressibility in the direction perpendicular to the line patterns and increased stiffness in the direction parallel to the line patterns. The line pattern functionalized graphene acted similar to a nanoscale mechanical spring. It is shown that clustered line pattern functionalization along the zigzag direction can increase the stiffness of the GS along the zigzag direction and stretchability along the armchair direction without significantly stretching the carbon bonds and can enhance the toughness of the GS relative to random functionalization. It was also found that the Poisson's ratio can be tuned from positive to negative through line pattern arrangements, reaching a minimum of -0.287 at an -OH percentage of 75% for stretching along the zigzag direction, thus indicating auxetic behavior. (c) 2019 Elsevier Ltd. All rights reserved.