Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: Poster: Charged Soft Matter

CPP 10.9: Poster

Montag, 14. März 2011, 17:30–19:30, P2

Structural changes of polycation covered surfaces induced by oxygen radicals — Markus Butto, Peter Nestler, •Florian Berg, Stephan Block, and Christiane A. Helm — Inst. für Physik, Uni Greifswald, Felix-Hausdorff-Str. 6, D-17487 Greifswald

Positively charged, branched polyethylenimin (PEI) is adsorbed onto silicon wafers and attacked by hydroxyl radicals. Changes of the PEI layer are monitored on the mesoscopic length scale by Au nanoparticle (AuNP) adsorption, using AFM imaging and UV-vis absorption. Bulk diffusion controls the AuNP adsorption. A lower saturation coverage of the AuNP demonstrates a decreased positive surface charge of the PEI layer after the radical attack. Also, we find a reduced diffusion constant of AuNPs. This is attributed to conformational changes of the PEI layer.

To measure the surface forces of a PEI layer before and after a radical attack the AFM colloidal probe (CP) technique is used. The force curves of PEI layers adsorbed from pure water show that the repulsive electrostatic force dominates the interaction (DLVO theory) and PEI adsorbs flatly. After attacking the PEI layer with hydroxyl radicals, the first force curves show a steric force suggesting PEI branches dangling into solution, additionally a short ranged attraction is found. Furthermore, the surfaces appear laterally inhomogeneous.