Wetting and non-wetting liquid flow in nanopores: Wettability, non-Poiseuille profile and intermolecular fundamentals

• Development of a novel nanoflow model based on 2D-NS equations. • The model uses position-dependent viscosity and considers the effect of wettability. • The model performs superior to routine MD techniques due to thermal noise effects. • Slip effect and interfacial viscosity control non-wetting liquid flow enhancement. • Effect of wettability on flowrate of wetting/partially liquids is demonstrated. Wetting and non-wetting liquid flow in nanoscale pores or channels is of great interest in many science and technology fields, such as biotechnology, energy storage/conversion and micro-devices. It is also of considerable significance in geosciences and geoengineering. For instance, for the geological disposal of contaminated waste understanding flow and transport in nanoporous rocks is critical for accurately evaluating potential environmental hazards. Similarly, for oil recovery from tight reservoirs, understanding flow mechanisms in nanopores may improve production forecasts and enable the development of strategies to enhance production. This paper presents a comprehensive study on wetting and non-wetting liquid flow in nanopores, including the development of a new nanoflow model and its demonstration using published findings from molecular dynamics simulations and laboratory tests. The new nanoflow model is formulated based on the general two-dimensional Navier-Stokes equations. The novel aspects include: 1) the model incorporates the parameters relating to the intermolecular interactions between the fluid and the solid wall in a nanopore, which are lacking in traditional continuum models; 2) the model contains the effects of wettability and the nanochannel’s dimension on flowrate, which are unique to nanoflows and not considered in traditional continuum models; and 3) the model is based on a two-dimensional non-Poiseuille flow model described by a set of coupled ordinary differential equations. Therefore, the numerical solutions are much easier to obtain than the partial differential equations of non-Poiseuille flow models. The classic Poiseuille flow is its limiting case. Three examples are presented to demonstrate the model’s capability. The first is the determination of the contact angle of water in hydrophobic carbon nanochannels or nanotubes using published results from MD simulations and laboratory tests. The second example uses the new nanoflow model to simulate non-wetting water flow in hydrophobic nanochannels or nanotubes, including flow in a nanoscale graphene slit representative of those present in graphene batteries for energy storage. The results obtained are compared with those obtained from MD simulations. The last example discusses the wetting or partially wetting liquid flow profiles in nanoscale pores. The three examples provide new insights into wetting and non-wetting liquid flow behaviour in nanopores.