Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Weiche Materie Poster: Do., 13:00–15:30 D-P340
Liquid-gas interfaces studied by x-ray reflectivity
Felix Lehmkühler 1 , Michael Paulus 1 , Metin Tolan 1
1 Experimentelle Physik Ia, Universität Dortmund, Maria-Göppert-Mayer-Straße 2,
44227 Dortmund
The polypropylene glycol 4000 (PPG4000) - isobutane interface was studied by x-ray
reflectivity measurements. The interface was investigated under different pressures
between 1.0 bar and 2.6 bar which is close to the condensation pressure of isobutane
at the temperature of 289 K. While adsorption of molecular thin films of isobutane is
expected for hydrophobic interacting systems like glycerol-isobutane or water-propane,
the formation of isobutane films on PPG4000 surface is suppressed by the high miscibility
of isobutane and PPG4000. Thus no evidence for the formation of isobutane
films was found.
The surface roughness of the substrate was estimated to vary between σN2 = 4 ˚A at
1 bar N2 and σ2.6 = 8 ˚A at 2.6 bar isobutane pressure. This is explained by the change
of surface tension of the PPG4000-isobutane mixture with isobutane pressure.
Ideal solution of isobutane in PPG4000 regarding to Raoult’s Law [1] is assumed to describe
the measurements. The surface tension γ is calculated with the capillary waves
theory to confirm the ideal solution with theoretical models for surface tension behavior
of binary liquid mixtures. The Parachor-method [2] and gradient theory [3] are
applied. The measurements show very good agreement with the theoretical calculation.
[1] P.W. Atkins, Kurzlehrbuch Physikalische Chemie, Spektrum Akademischer Verlag,
Heidelberg (1993)
[2] S. Sugden, J. Chem. Soc. Trans., 1924, 1177-1189
[3] V. Bongiorno, H.T. Davis, Phys. Rev. A, 12, 2213-2224 (1975)