Thermodynamically\nDependent Behavior in Gas Transport\nin Two-Dimensional Graphene Nanochannels

Gas transport through nanochannels has aroused significant\ninterest\nin many fields. Recently, “ballistic transport” of gas\nwas observed through a two-dimensional graphene nanochannel, and it\ncauses a peculiar enhancement compared to the predictions of the Knudson\ntheory. Many studies attributed this effect to the specular reflection\ncaused by the atomically smooth surface of the channel. Here, our\nmolecular dynamics simulation, showing consistent results with previous\nexperiments and simulations, reveals an interesting aspect: gas atoms\nwith higher kinetic energies tend to pass the channel more easily.\nExtensive calculations of the tangential momentum accommodation coefficient\nconsidering different velocities on the graphene surface reveal that\nthe attractive force between the gas and the surface atoms plays a\nmore prominent role than the previous view, and gas atoms with more\nnormal kinetic energies will overcome the attraction. Consequently,\nit indicates that a constant parameter used to balance the specular\nand diffuse reflection may not be adequate and should be replaced\nby a function considering the thermodynamic properties of gases.