Bending modes, elastic constants and mechanical stability of graphitic systems

The thermodynamic and mechanical properties of graphitic systems are strongly dependent on the shear elastic constant C44. Using state-of-the-art density functional calculations, we provide the first complete determination of their elastic constants and exfoliation energies. We show that stacking misorientations lead to a severe lowering of C44 of at least one order of magnitude. The lower exfoliation energy and the lower C44 (more bending modes) suggest that flakes with random stacking should be easier to exfoliate than the ones with perfect or rhombohedral stacking. We also predict ultralow friction behaviour in turbostratic graphitic systems.

Graphical abstractUsing ab initio method, which includes van der Waals interactions, we show that turbostratic stacking lowers the corrugation and exfoliation energies. The lower corrugation energy decreases C44 and gives rise to ultralow friction behaviour in turbostratic graphitic systems. Our results indicate that flakes with turbostratic stacking are easier to exfoliate.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Turbostratic stacking lowers the corrugation and exfoliation energies. ► The lower corrugation energy decreases C44 and more bending modes are excited. ► Flakes with turbostratic stacking are easier to exfoliate. ► Ultralow friction behaviour is predicted in turbostratic graphitic systems.