Investigating liquid-solid interfacial phenomena in a Couette flow at nanoscale

This study investigates shear-induced liquid structure changes in nanoscale Couette flows and their corresponding flow boundary conditions. Molecular dynamics simulations are used to model a liquid argon slab confined between two smooth rigid copper walls with an applied velocity at the upper wall to generate a planar Couette flow. Depending on the applied wall velocity, different liquid structures or the orderings of the liquid at liquid-solid interfaces are identified when reaching steady states. We define three regimes based on the ordering of the liquid structure: Newtonian, layer, and oversheared. Each regime is characterized by the spatial probability distribution and structure factor. These liquid structures are strongly correlated with the liquid velocity and density profiles in the flow. Ultimately, the liquid structures also determine the boundary conditions from pure slip to multilayer locking at liquid-solid interfaces. Our results show that temperature and liquid-solid interaction parameter are also important factors in influencing the liquid structures formed near interfaces.