Molecular dynamics simulation study of the dynamics of fluids in thin films

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Abstract
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 configuration. In addition, the dynamics perpendicular to solid surfaces of the hexadecane molecules as well as of a simple Lennard-Jones fluid is investigated. For the Lennard-Jones fluid, the numerical results are compared with analytical calculations based on the diffusion equation, which shows that the numerical results can very well be described by the solution of the diffusion equation for reflecting surfaces. The diffusion coefficient is practically independent of the position within the film, although the fluid is inhomogeneous perpendicular to the surfaces. However, we observe a slight influence of the finite size of the fluid particles on their dynamics in the layer adjacent to a surface. In contrast, the dynamics of the centers of mass of hexadecane molecules perpendicular to repulsive surfaces is severely slowed down due to their extended and anisotropic nature and cannot be described by a single particle diffusion equation.