Eur. Phys. J. E 15, 13-17 (2004)
DOI: 10.1140/epje/i2004-10031-3

Phase behaviour of -hexane/perfluoro- -hexane binary thin wetting films

W. Prange¹, W. Press^{1, 2}, M. Tolan³ and C. Gutt<sup>3

1</sup>  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

gutt@physik.uni-dortmund.de

(Received 28 April 2004 / Published online: 21 September 2004)

Abstract
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.

PACS
61.10.Kw - X-ray reflectometry (surfaces, interfaces, films).
64.75.+g - Solubility, segregation, and mixing; phase separation.
68.15.+e - Liquid thin films.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2004