  The understanding of water transport in graphene oxide (GO) membranes stands
out as a major theoretical problem in graphene research. Notwithstanding the
intense efforts devoted to the subject in the recent years, a consolidated
picture of water transport in GO membranes is yet to emerge. By performing
mesoscale simulations of water transport in ultrathin GO membranes, we show
that even small amounts of oxygen functionalities can lead to a dramatic drop
of the GO permeability, in line with experimental findings. The coexistence of
bulk viscous dissipation and spatially extended molecular friction results in a
major decrease of both slip and bulk flow, thereby suppressing the fast water
transport regime observed in pristine graphene nanochannels. Inspection of the
flow structure reveals an inverted curvature in the near-wall region, which
connects smoothly with a parabolic profile in the bulk region. Such inverted
curvature is a distinctive signature of the coexistence between single-particle
Langevin friction and collective hydrodynamics. The present mesoscopic model
with spatially extended friction may offer a computationally efficient tool for
future simulations of water transport in nanomaterials.
