Scale effect on simple liquid transport through a nanoporous graphene membrane

Abstract

The transport mechanism of simple liquid through nanoporous graphene membranes (NPGMs) with pores of various diameters has been explored by utilizing non-equilibrium molecular dynamics (NEMD) simulation. The flow is initiated using a pressure-driven flow mechanism that moves the specular reflection wall at a constant velocity. Both the local density peak near the membrane and the pressure drop are dependent on the pore diameter. For accurate calculation of velocity profile inside the nanopore, we implemented three boundary approaches and local nanoscale variants to see the effect of these factors on the nature of the nanoscale flow. We found an optimized definition of pore boundary, which minimizes the deviation between MD results and slip-viscosity-modified Sampson’s prediction for nanopores of various diameters. Additionally, we observed that with decreasing pore size, the pore center velocity increases, as does the slip velocity, which we attributed to van der Waals interaction between liquid and wall atoms inside the nanopore. However, the effects of slip velocity, interfacial viscosity, and pore boundary decay exponentially with increasing pore diameter because of the dominance of van der Waals repulsive forces at the molecular level.