Effect of wall roughness on shear viscosity and diffusion in nanochannels

The effect of wall roughness on liquid argon shear viscosity and diffusion coefficient in nanochannels is studied by non-equilibrium molecular dynamics. Diffusion coefficient results are presented in terms of average values for the whole channel, as well as profiles of local values calculated in layers along the channel. It turns out that the local diffusion coefficient decreases significantly in fluid layers adjacent to the rough wall due to the trapping of fluid atoms inside the rough wall cavities. The degree of anisotropy in the x-, y- and z-components of the diffusion coefficient close to the rough wall increases relative to the anisotropy observed close to the smooth wall. Stress tensor components as well as local strain rates are evaluated in order to extract the coefficient of shear viscosity, ηs, which presents significant variations near the rough wall. These results should be taken into consideration when it comes to the design of nanofluidic devices.