WATER PERMEATION THROUGH GRAPHENE NANOSLIT BY MOLECULAR DYNAMICS SIMULATION

T Yamada and R Matsuzaki, ICCM 21: 21ST INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS (ICCM-21) (2017).

In this study, to elucidate flow mechanisms at the nanoscale, we conducted water-permeation simulation for graphene slits. In nanoscale flows, the influence of the channel wall is relatively large, and it has been confirmed that the traditional continuum model based on continuity equations fail to provide accurate predictions. Usually, the Knudsen number (Kn) is used to show the applicability of the continuum laws. However, the applicability of this dimensionless parameter is experimentally established, and the exact value at which deviation occurs and the reason for the deviation cannot be explained. We calculated the permeability of the flow through a slit by using classical molecular dynamics (MD) for various Kn, and compared the MD simulation results with predictions obtained from the continuum model. We considered two hydrodynamic models: one for a non-slip condition with velocity = 0 on the wall, and another for a slip condition with finite velocity us on the wall, where the velocity is proportional to pressure difference before and after permeation. The permeability values determined from MD results agree well with the results of the slip model in the range Kn < 0.375, but the values differed in the range Kn > 0.375. Additionally, from the density profile, we found that water molecules passing through a slit form high-density layers at a certain distance from the wall. When the numbers decreases to one, the flow changes from a slip flow to a free-molecular flow. This study provides guidelines for understanding flow mechanisms at the nanoscale and for the development of graphene filtration membranes.

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