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Weiche Materie Poster: Do., 13:00–15:30 D-P346
A grazing incidence diffraction study of aqueous salt solutions and water
Michael Paulus 1 , Christian Gutt 2 , Christof Krywka 1 , Michael Sprung 3 ,
Metin Tolan 1
1 Experimentelle Physik I, DELTA, Universität Dortmund, Maria-Goeppert-Mayer Str.
2, 44227 Dortmund – 2 Deutsches Elektronen Synchrotron (Hasylab), Notkestraße 85,
D-22607 Hamburg, Germany – 3 c/o 8ID/IMMY-XOR-CAT, APS/ANL, Argonne, IL,
60439, USA
We report in-situ grazing incidence x-ray diffraction (GID) experiments to study aqueous
solution-gas interfaces of the sodium halogenides NaCl, NaBr and NaI performed
at ID10B, ESRF. The out-of-plane diffusely scattered signal yields information about
the lateral structure of the investigated samples surface. The scattered signal can be
used to test the simple capillary waves model down to nanometer length scales. Using
the Distored Wave Born Approximation (DWBA) for the data analysis, a possible
wave vector dependence of the surface tension can be determined. GID scans of the
salt solutions (5 molar) and pure water were performed up to wave vector transfers
parallel to the surface q|| of approximately two inverse angstroms. The measured data
for the salt solutions and pure water are compared with theoretical calculations of the
scattered signal based on the DWBA theory using both, a constant surface energy and
a wave vector dependent surface energy based on the work of Mecke et al [1] . For a
better description of the data, measurements of the bulk structure factors of all liquids
were performed at the synchrotron source DELTA, BL9.
The refinements of these measured structure factors were included into the calculations
of the diffusely scattered signal. We observe for all liquids a reduction of the surface
energy at short length scales. This effect seems to be similar for all liquids and will
be explained in an alternative way by inclusion of lateral movements into the capillary
waves model.
[1] Mecke et al., Phys. Rev. E 59 (6) 6766 (1999)