|During the last ten years, there has been enormous interest in understanding transport phenomena in micro and nanofluidic systems and, in particular, in accurate prediction of fluid flows with slip boundary conditions at liquid-solid interfaces. In this presentation we will discuss recent results obtained from molecular dynamics simulations of model fluids that consist of monomers or linear polymer chains confined by flat crystalline surfaces. The effects of shear rate and wall lattice orientation on the slip behavior are studied for a number of material parameters of the interface, such as fluid and wall densities, wall-fluid interaction energy, polymer chain length, and wall lattice type. A detailed analysis of the substrate-induced fluid structure and interfacial diffusion of fluid molecules is performed to identify slip flow regimes at low and high shear rates.
It was found that at sufficiently high shear rates, the slip flow over flat crystalline surfaces is anisotropic, i.e., the slippage is enhanced when the flow direction is parallel to the crystallographic axis of the substrate. Furthermore, it is demonstrated numerically that the friction coefficient (the ratio of shear viscosity and slip length) undergoes a transition from a constant value to the power-law decay as a function of the slip velocity. The characteristic velocity of the transition correlates well with the diffusion velocity of monomers in the first fluid layer. We also show that in the linear regime, the friction coefficient is well described by a function of a single variable, which is a product of the magnitude of surface-induced peak in the structure factor and the contact density of the adjacent fluid layer.