Dresden 2011 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: Poster: Charged Soft Matter

CPP 10.8: Poster

Monday, March 14, 2011, 17:30–19:30, P2

Equilibrium and non-equilibrium features in the structure of physisorbed poly(styrene sulfonate) layers — •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 NaCl solutions with an ionic strength ranging between 0 M and 1 M NaCl. Colloidal probe tapping mode imaging shows that domains of PSS brushes coexist with flatly adsorbed PSS. The brush area fraction increases with rising degree of polymerization. The surface forces are a superposition of steric and electrostatic forces, their respective contribution is determined by the brush area fraction.

Unexpectedly, the internal properties of the brush domains (i.e. brush thickness and average chain distance) are independent on the deposition salt concentration. They increase with rising polymer length, while the brush thickness can also be controlled by the surrounding salt concentration (equilibrium feature).

These properties suggest that flatly and brush-like physisorbed chains can be understood as two different PSS phases, whereby the ratio of both phases is controlled by the salt concentration in the deposition solution. Furthermore, the amount of brush-like physisorbed PSS chains is related to the increase in PSS surface coverage, which is also observed after addition of salt to the deposition solution with other techniques and which is extensively described in literature.