Two-dimensional non-linear hydrodynamics and nanofluidics

A water monolayer squeezed between two solid planes experiences strong out-of-plane confinement effects while expanding freely within the plane. As a consequence, the transport of such two-dimensional water combines hydrodynamic and nanofluidic features, intimately linked with each other. In this paper, we propose and explicitly solve a non-linear hydrodynamic equation describing two-dimensional water flow with viscosity parameters deduced from molecular dynamic simulations. We demonstrate that the very ability of two-dimensional water to flow in short channels is governed by the second (dilatational) viscosity coefficient, leading to flow compression and velocity saturation in the high-pressure limit. The viscosity parameter values depend strongly on whether graphene or hexoganal boron nitride layers are used to confine 2D water that offers an interesting opportunity to obtain various nanofluids out of the same water molecules just by using alternate materials to fabricate the 2D channels. Confining a liquid in two-dimensions, such as between sheets of graphene, can give rise to unexpected behaviour, particular in the case of water due to the presence of strong hydrogen bonding. Here, the authors present a hydrodynamic model for the flow of a monolayer of water confined in a 2D channel, showing the properties are governed by a dilatational viscosity coefficient.