DIFFUSIVE MOTION IN CONFINED FLUIDS - MODE-COUPLING RESULTS AND MOLECULAR-DYNAMICS CALCULATIONS

We present a mode-coupling calculation of the self-diffusion coefficie nt in a Liquid confined between two parallel solid walls. The effect o f confinement is to lower the diffusion constant in the direction para llel to the walls, compared to the bulk case. The relative decrease be haves as (sigma/h) log(h/sigma), where h is the thickness of the fluid slab, and sigma the atomic size. This behaviour is interpreted in ter ms of the suppression of long-wavelength modes due to confinement. It is also explained by a simple hydrodynamic argument. Molecular-dynamic s simulations confirm the theoretically predicted behaviour, even at r ather small values of h.