Interaction between a water drop and holey graphene: retarded imbibition and generation of novel water-graphene wetting states.

Transport of water through a holey or nanoporous graphene structure in presence of an external force (e.g., a pressure gradient) has paved the way for a myriad of applications ranging from water desalination to water-alcohol separation. In this study, on the other hand, we employ molecular dynamics (MD) simulations to probe no-external-force imbibition/permeation of a water nanodrop through a multilayer holey graphene structure. We carry out MD simulations in a two-dimensional set up; consequently, the holes in the graphene sheets appear as lateral separations between finite-length graphene layers, while the inter-layer distances appear as vertical separations. Interplay of lateral and vertical separations triggers combined spreading-imbibition dynamics, enforcing highly non-trivial water-graphene wetting states such as wetting-induced encapsulation of a complete graphene stack by the water drop, simultaneous wetting of multiple surfaces of multiple graphene stacks, and wetting with pinned and unpinned contact lines on vertically separated graphene layers. Finally, under certain combinations of lateral and vertical ISSs, there can be wetting of a much larger surface area of graphene, which is useful in applications (e.g., enhanced energy storage or heat transfer) favored by enhanced graphene-water contact area. Therefore, the present study has a twofold objective: first, it unravels, for the first time, water-holey graphene imbibition dynamics, and second, it identifies imbibition-triggered novel water-graphene wetting states for improving realistic applications involving graphene and water.