Berlin 2008 – scientific programme

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 5: Poster Session SYSA

SYSA 5.90: Poster

Tuesday, February 26, 2008, 14:30–20:00, Poster A

Long-ranged steric forces between poly(styrene sulfonate) covered surfaces — •Stephan Block and Christiane A. Helm — Institut für Physik, Ernst-Moritz-Arndt Universität, Felix-Hausdorff-Str. 6, D-17487 Greifswald, Germany

We investigate distance dependent surface forces with Colloid Probe Technique (CPT) between poly (styrene sulfonate) (PSS) coated surfaces in salt solutions between 1 mM and 1 M, after the PSS was adsorbed from 1 M NaCl solution onto Si surfaces positively charged by silanization. A non-flat conformation is observed [1]. The theory of Alexander and de Gennes for interacting surfaces covered with neutral anchored polymers describes the long-ranged steric interaction between the PSS layers. A lack of electrostatic interaction and the scaling of the layer thickness similar to polyelectrolyte brushes suggest that the polyelectrolytes are neutralized by counterions incorporated into the layer. Investigation of asymmetric surfaces (one PSS covered surface against a silica colloidal probe or a silicon tip) supports this picture, since decay length and amplitude of the force are halved compared to the forces between two identical surfaces. After drying (0% r.h.) and reimmersion into solution the surface forces between the PSS layers are almost unchanged, suggesting strong local bonds between few monomers and the substrate. Furthermore, on increase of the PSS molecular weight (78kDa, 350kDa and 1.3MDa) the PSS layer thickness as well as the distance between adsorption points increases.

[1] S.Block and C.A.Helm, PRE 76 (2007) 030801(R).