Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Interfaces and Thin Films II

CPP 18.5: Talk

Tuesday, March 23, 2010, 15:00–15:15, H39

Single polyelectrolyte layers adsorbed at high salt conditions: polyelectrolyte brush domains coexisting with flatly adsorbed chains — •Stephan Block and Christiane A. Helm — Institut für Physik, Ernst-Moritz-Arndt Universität, Felix-Hausdorff-Str. 6, D-17489 Greifswald, Germany

AFM is used to measure the surface forces and to image sodium poly(styrene sulfonate) (PSS) layers physisorbed from 1 M NaCl solution on different length scales within one experiment. Domains of PSS brushes coexist with flatly adsorbed PSS. For degree of polymerization N = 380, the brush area fraction 6 %. With increasing degree of polymerization, brush area fraction and domain size increase, while the domain radii range from 50 nm up to 1500 nm. Laterally homogeneous brush layers are found for a degree of polymerization exceeding 1100. Colloidal probe technique reveals that the surface forces are a superposition of steric and electrostatic forces, their respective contribution is determined by the brush area fraction. A comparison with literature demonstrates that adsorbed PSS brushes show the same scaling behaviour as end-grafted PSS brushes. We develop a model for the adsorption of polyelectrolytes in which not the whole chain but only a fraction of the monomers adsorbs onto the surface. Thereby we show that partial adsorption can lead to stable conformations and calculate scaling laws for the fraction of adsorbed monomers and the distance between the chains dangling into solution.