Flow resistance analysis of nanoconfined water in silt pores by molecular simulations: Effect of pore wall interfacial properties

Abstract

The anomalous flow behavior of nanoconfined water is attracting considerable attention. This study aimed to investigate the effect of pore wall interfacial properties on the flow behavior of water confined in a slit pore. Non-equilibrium molecular dynamics simulations were performed on water molecules confined in slit pores. By moving the two pore walls to opposite directions, the confined water molecules were made in a directed flowing. The flow resistance of the water molecules was then analyzed at the nanoscale. Two Si(111) surfaces were used to construct the slit pore model. The interaction strength, ɛSi-w, between the pore wall atom and water's oxygen atom was adjusted to represent different pore wall interfacial properties. A higher ɛSi-w indicates a more hydrophilic pore wall interface. Simulation results show that for the studied cases, more hydrophilic pore walls leads to larger flow resistance of the confined water. At the molecular level, the friction between the pore wall and water molecules increases with increased hydrophilicity of pore walls and further hampers the flow of the confined water in the slit pore. Moreover, simulation results demonstrate that water molecules confined in the slits are layered. The increase in the hydrophilicity increases hydrogen bonds between water layers, thereby enhancing flow resistance arising from the water molecules themselves.