Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 34: POSTERS Polymerphysics
CPP 34.58: Poster
Donnerstag, 28. Februar 2008, 17:00–19:30, Poster A
Water incorporation in poylectrolyte multilayers: Hofmeister effect? — •Oxana Ivanova1, Olaf Soltwedel1, Manesh Gopinadhan1, Jens-Uwe Günther1, Matthias Cornelsen1, Roland Steitz2, and Chrstiane A. Helm1 — 1Institut für Physik,Ernst-Moritz-Arndt Universität,Felix-Hausdorff-Straße 6, 17489 Greifswald,Germany — 2Hahn-Meitner Institut, Glienicker Straße 100, D-14109 Berlin, Germany
The Hofmeister effect - the effect of salt on the hydrophobic effect - on the formation of polyelectrolyte multilayers is studied. Films are prepared while varying the preparation temperature T and the countercation (1 M XCl). For characterization, X-ray and neutron reflectivity are used. Selectively deuterated polyanion layers lead to at least two superstructure peaks. The PAH/PSS bilayer thickness is independent of the kind of salt and increases on temperature rise. Yet, at low T the amount of bound water depends strongly on the position of the cation in the Hofmeister series (Cs+<Ka+<Na+). The internal roughness is 30-40 % of the bilayer thickness; it increases to up to 60% at high T. The temperature at which the roughening starts is a function of the countercation (ca. 50∘C for NaCl, ca. 40∘C for KCl and ca. 30∘C for CsCl). It appears that the temperature effect - which is attributed to the melting of the first-shell water on temperature rise - is promoted by the countercations as predicted by the Hofmeister series. The effect is subtle; it manifests itself as an increased internal roughness, a loss of bound water and a downshift of the roughening temperature - whereas the thickness of the deposited bilayer is not affected.