| Abstrakt: |
Two-dimensional (2D) material-based membrane separation has attracted increasing attention due to its promising performance compared with traditional membranes. However, in-depth understanding of water transportation behavior in such confined nanochannels is still lacking, which hinders the development of 2D nanosheets membranes. Herein, we investigated water confined in graphene or MoS2 nanochannels by molecular dynamics (MD) simulations and found water's diffusivity always varied linearly with their mean square displacement along z direction (〈Δz2〉) when system variables (e.g., water molecules' number, channel height, nonbonded interaction parameter, and harmonic potential constraining water's z-coordinate) changed. Such linear correlation applies to different water models and different force fields (FFs) of channel walls (e.g., different Lennard-Jones parameters or even flexible FF), no matter whether water molecules form 3-, 2-, or quasi-2-layer structure in the nanochannel. This indicates, though water molecules' motion along z direction (z-fluctuation, confined within 1 nm) and that in xy plane (xy-diffusion) are entirely different, they are tightly coupled: Violent z-fluctuation would produce more transient void to facilitate xy-diffusion, which is to the sharp contrary of bulk water, where motions in x, y, and z directions are symmetric, but independent. Our work could help design high performance 2D nanochannels and discover more novel principles in nano-fluidics and membrane separation fields. [ABSTRACT FROM AUTHOR] |
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