Phase behaviour of n-hexane/perfluoro-n-hexane binary thin wetting films
Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Leibnizstraße 17-19, D-24098, Kiel, Germany
2 Institut Laue-Langevin, 6, rue Jules Horowitz, F-38042, Grenoble Cedex, France
3 Fachbereich Physik, Universität Dortmund, Otto-Hahn-Straße 4, D-44221, Dortmund, Germany
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We present X-ray reflectivity investigations of the concentration distribution in binary liquid thin films on silicon substrates. The liquid-vapor coexistence of the binary mixture investigated, hexane and perfluorohexane, is far from criticality. Therefore, a sharp interface separates the liquid film from the vapor. The data reveal a separation of the film in layers parallel to the substrate. A phase diagram is constructed as a projection to the (composition difference, temperature) space, covering a temperature range corresponding to the one-phase and the two-phase regime of the bulk liquid. Although the composition data indicate a mixing gap similar to that of the bulk system, there are two major differences: i) only the near-surface phase changes its composition significantly, and ii) a composition gradient in the film exists also at higher temperatures where in the bulk system the one-phase regime exists.
© EDP Sciences, Società Italiana di Fisica, and Springer-Verlag, 2004