Turbostratic Orientations, Water Confinement and Ductile-Brittle Fracture in Bi-layer Graphene

Bi-layer graphene (BLG) can be a cheaper and more stable alternative to graphene in several applications. With its mechanical strength being almost equivalent to graphene, BLG also brings advanced electronic and optical properties to the table. Furthermore, entrapment of water in graphene-based nano-channels and devices has been a recent point of interest for several applications ranging from energy to bio-physics. Therefore, it is crucial to study the over-all mechanical strength of such structures in order to prevent system failures in future applications. In the present work, Molecular Dynamics simulations have been used to study crack propagation in BLG with different orientations between the layers. There is a major thrust in analyzing how the angular orientation between the layers affect the horizontal and vertical crack propagation in individual layers of graphene. The study has been extended to BLG with confined water in interfaces. Over-all strength of graphene sheets when in contact with water content has been determined, and prominent regional conditions for crack initiation are pointed out. It was seen that in the presence of water content, graphene deviated from its characteristic brittle failure and exhibited the ductile fracture mechanism. Origin of cracks in graphenes was located at the region where the density of water dropped near the graphene surface, suggesting that the presence of hydroxyl groups decelerate the crack formation and propagation in straining graphenes.