Dresden 2009 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Polyelectrolytes

CPP 18.9: Talk

Tuesday, March 24, 2009, 11:45–12:00, ZEU 114

Conformation of poly(styrene sulfonate) layers physisorbed from high salt solution studied by force measurements on two different length scales — •Stephan Block and Christiane A. Helm — Institut für Physik, Uni Greifswald, Felix-Hausdorff-Str. 6, 17487 Greifswald

The colloidal probe technique (CPT) is used to measure distance-dependent interaction forces between polyelectrolyte layers physisorbed from 1 M NaCl solution in salt solutions between 0.1 mM and 1 M. Both linear polycations (poly(allylamine)hydrochloride, poly-l-lysine) and linear polyanions (poly(styrenesulfonate)) are used. The repulsive interaction energies in the range between 10(-7) and 10(-4) J/m(2) are described by the theory of Alexander and de Gennes for surfaces covered with neutral anchored polymers. However, the brush thickness scales with molecular area and salt concentration with a power of -1/3 as known from a salted brush and reaches approximately 50% of the contour length in diluted solutions. For PSS at low salt conditions, the brush length amounts to 30% of the contour length, a behavior known for polyelectrolyte brushes and attributed to the entropy of the counterions trapped in the brush. A negatively charged AFM tip penetrates the brush-a repulsive electrostatic force between the tip and surface is found, and single chains can be imaged. Thus, with the nanometer-sized AFM tip, the flatly adsorbed fraction of the PSS chains is seen, whereas the micrometer-sized colloidal probe interacts with the fraction of the chains penetrating into solution.