Regensburg 2007 – scientific programme
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SYPE: Symposium Polyelectrolytes
SYPE 2: Polyelectrolytes I
SYPE 2.8: Talk
Thursday, March 29, 2007, 16:30–16:45, H37
Bundle Formation in Polyelectrolyte Brushes — •Jens-Uwe Günther1, Heiko Ahrens1, Stephan Förster2, and Christiane Helm1 — 1Institut für Physik, Ernst-Moritz-Arndt Universität, F.-L.-Jahn-Str. 16, D-17487 Greifswald, Germany — 21Institut für Physikalische Chemie, Universität Hamburg, Bundesstr. 45, D-20146 Hamburg, Germany
Bundle formation in the vertically oriented chains of poly(styrene sulfonate) (PSS) within polyelectrolyte brushes is studied with grazing incidence diffraction as function of grafting density and ion concentration. The brush thickness determined with X-ray reflectivity amounts to 30-50% of the contour length. As predicted theoretically, bundle formation can be induced by adding divalent ions, ie CaCl2. However, at 0.5 Molar monomer concentration and without added salt, already bundles are observed. Then, a bundle consists of two chains and is 5 nm long. On the addition of up to 1 M CsCl in the subphase the aggregation number increases up to 20 whereas the bundle length approaches a limiting value, 2 nm. We suggest that the bundle formation is determined by a balance between long-ranged electrostatic repulsion, whose range and amplitude is decreased on salt addition, and a short-ranged attraction.