MOLECULAR-DYNAMICS SIMULATION STUDY OF THE DYNAMICS OF FLUIDS IN THIN-FILMS

The structure and dynamics of fluids in thin films are investigated by molecular dynamics simulations. Particularly the influence of surface attraction or repulsion on the structure of hexadecane melts (C16H34) is investigated. We find that for a strongly attractive surface, well ordered, crystalline like monolayers are the most stable configuratio n. In addition, the dynamics perpendicular to solid surfaces of the he xadecane molecules as well as of a simple Lennard-Jones fluid is inves tigated. For the Lennard-Jones fluid, the numerical results are compar ed with analytical calculations based on the diffusion equation, which shows that the numerical results can very well be described by the so lution of the diffusion equation for reflecting surfaces. The diffusio n coefficient is practically independent of the position within the fi lm, although the fluid is inhomogeneous perpendicular to the surfaces. However, we observe a slight influence of the finite size of the flui d particles on their dynamics in the layer adjacent to a surface. In c ontrast, the dynamics of the centers of mass of hexadecane molecules p erpendicular to repulsive surfaces is severely slowed down due to thei r extended and anisotropic nature and cannot be described by a single particle diffusion equation. (C) 1996 American Institute of Physics.