Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 27: POSTER Polymer Physics and Materials

CPP 27.4: Poster

Thursday, March 30, 2006, 17:00–19:00, P2

Surface roughness and adsorption isotherms of molecularly thin liquid films — •Michael Paulus¹, Cristian Gutt², and Metin Tolan¹ — ¹Institute of Physics, University of Dortmund, D-44221 Dortmund, Germany — ²Deutsches Elektronen Synchrotron (Hasylab), Notkestraße 85, D-22607 Hamburg, Germany

We present an x-ray reflectivity study of molecularly thin adsorbed isobutane films on liquid glycerol. The interaction between the isobutane and the liquid glycerol is usually dominated by long-range van der Waals interaction which gives rise to the formation of thin films of gas molecules on the glycerols surface. Surfaces of liquids are modulated by thermally excited capillary wave fluctuations. Concerning thin films, this capillary wave fluctuations are strongly suppressed by the substrate-film interaction. This leads to a layer thickness dependent roughness of thin adsorbed films. The x-ray reflectivity measurements provide both, the adsorption isotherms and the rms roughness of the adsorbed film. The measured surface roughness of the isobutane film is smaller than expected from a calculation based on a harmonic approximation of the interaction potential. It turned out that the calculation of surface roughness of molecularly thin adsorbed films leads to good agreement with experiment, only when higher order terms of the interaction potential are considered. This is causally connected by the strong coupling between the glycerol and layer surface at low layer thickness.