MICROSCOPIC DYNAMICS OF FLUIDS CONFINED BETWEEN SMOOTH AND ATOMICALLYSTRUCTURED SOLID-SURFACES

Molecular dynamics and the grand canonical Monte Carlo techniques are employed to simulate the structure and dynamics of a fluid in a slit m icropore at equilibrium and under Couette flow. Calculated quantities include the fluid's density profiles, pair correlation functions, diff usion coefficients, normal pressure, stress tensor, and velocity profi les. Simulation results for fluids in equilibrium with the same bulk f luid, but confined by either atomically smooth or structured face cent ered cubic pore walls are compared. At the conditions considered, flui d in the contact layer next to structured walls exhibits enhanced flui d order which is not altered by flow for pores capable of accommodatin g two fully developed fluid layers (i.e., for pores wider than 2.5 mol ecular diameters across). At narrower pore widths, the equilibrium flu id structure is changed by flow and the fluid is more sensitive to she ar-induced changes in the diffusivity and normal pressure. The layer a verage density profiles of the confined fluid are similar in the struc tured and smooth pores. However, in the fluid layers adjacent to the s tructured pore walls, the local density distributions are ordered with a periodicity reflecting that of the atomic structure of the pore wal ls. At the strongest fluid-wall interaction considered, the confined f luid does not solidify although the diffusion coefficient of the fluid confined by the structured walls is reduced by as much as a factor of 87 compared to the bulk phase.