Surface energy and wettability of van der Waals structures

The wetting behaviour of surfaces is believed to be affected by van der Waals (vdW) forces; however, there is no clear demonstration of this. With the isolation of two-dimensional vdW layered materials it is possible to test this hypothesis. In this paper, we report the wetting behaviour of vdW heterostructures which include chemical vapor deposition (CVD) grown graphene, molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) on few layers of hexagon boron nitride (h-BN) and SiO 2 /Si. Our study clearly shows that while this class of two-dimensional materials are not completely wetting transparent, there seems to be a significant amount of influence on their wetting properties by the underlying substrate due to dominant vdW forces. Contact angle measurements indicate that graphene and graphene-like layered transitional metal dichalcogenides invariably have intrinsically dispersive surfaces with a dominating London-vdW force-mediated wettability. Our study shows that the surface energy of all 2D layered materials is undoubtedly dominated by London-van der Waals forces with little contribution from dipole-dipole interactions.