Regensburg 2007 – scientific programme

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SYPE: Symposium Polyelectrolytes

SYPE 1: Polyelectrolytes Poster

SYPE 1.11: Poster

Wednesday, March 28, 2007, 16:00–18:30, Poster B

Measurement of long-ranged steric forces between polyelectrolyte covered surfaces — •Stephan Block and Christiane Helm — Institut für Physik, Ernst-Moritz-Arndt Universität, F.-L.-Jahn-Str. 16, D-17487 Greifswald, Germany

Colloidal Probe Technique (CPT) is used to investigate the distance dependent interaction force between polyelectrolyte coated surfaces in salt solutions between 0.1 mM and 1 M, with the polyelectrolyte layers adsorbed from 1 M NaCl solution. As polyelectrolytes poly(allylamine) hydrochloride (PAH), Poly-L-Lysine (PLL) and poly (styrene sulfonate) (PSS) are used, the latter on Si surfaces which are positively charged by silanization.

The repulsive surface forces are more long-ranged with decreasing salt concentration and their decay length always exceed the Debye length. It can be described by the theory of Alexander and de Gennes for interacting surfaces covered with neutral anchored polymers. Apparently, the polyelectrolyte layer is swollen and loops and tails of the adsorbed polyelectrolyte layer dangle into the solution.

There is no approach-separation hysteresis and no influence of the history of the experiment, ie if the salt concentration is increased or decreased by several orders of magnitude. The situation is very different from the well-known flat polyelectrolyte adsorption layers obtained from salt free solutions, where the interaction force is purely electrostatic.