Regensburg 2002 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 15: Poster: Dünne Filme, Monolagen und Oberfl
ächen

CPP 15.6: Poster

Wednesday, March 13, 2002, 16:30–18:00, B

Structure and Dynamics of Liquids at Solid Surfaces — •Frank Cichos, Jörg Schuster, and Christian von Borczyskowski — Institut für Physik 122501, TU Chemnitz, 09107 Chemnitz

Liquids show a layering effect at solid surfaces, which is similar to the near order that is present in liquids. Density oscillations decaying on length scales of a few nanometers from the surface have been found and could strongly depend on the chemical nature of the solid substrate. To explore these differences, we have carried out molecular dynamics simulations of propanol on graphite and muscovite MICA as well as simulations of tetrakis(2-ethylhexoxy)silane (TEHOS) on silicon. In all simulations we find a layering up to a few nanometers perpendicular to the surface. Propanol molecules on graphite lye flat on the surface in a fishbone-like structure. No freezing of the bottom propanol layer occurs. Propanol on MICA shows however a rather complicated surface structure. Molecules are lying partly flat or standing upright on the surface. In addition we calculate a low mobility of the bottom layer, which increases to the bulk mobility within a few nanometers. Thus a transition from frozen propanol directly on the MICA surface to liquid propanol at a distance of 3 nm from the surface is found. TEHOS which is used in a variety of wetting experiments shows also clear layering, which is comparable to the layering detected in x-ray diffraction experiments. The distance dependence of the self diffusion coefficient nicely compares to single molecule diffusion experiments in thin TEHOS films on silicon oxide.