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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 7: POSTER: INTERNAL SYMPOSIUM Scattering Experiments

CPP 7.31: Poster

Montag, 26. März 2007, 16:00–18:00, Poster B

Water uptake and exchange kinetics of polyelectrolyte films: A neutron reflectometry study — •Regine v. Klitzing¹, John Wong¹, and Roland Steitz² — ¹TU Berlin, Stranski-Laboratorium, Straße des 17. Juni 124, D-10623 Berlin — ²Hahn-Meitner-Institut, SF1, Glienicker Str. 100, D-14109 Berlin

The sequential layer--by--layer adsorption of polyanions and polycations to build polyelectrolyte multilayers has triggered enormous interest in their potential uses in a wide range of fields, from photonic to pharmaceutical applications. We will show that the conformation of the solvent swollen films -- prior to drying -- is determined by the initial adsorption conditions, but can be altered ex-situ by exposure to a liquid phase of very high ionic strength. Recently it has been observed that the swelling depends on the charge of the outermost layer. In the PAH/PSS system we saw that assemblies with PSS as the outermost layer swell more than those with PAH outside. A neutron reflectivity study of this effect in addition indicated the existence of two kinds of water, bound with different strength within the films. Beside an unexpected two-step kinetics of swelling, the reflectivity curves of the layers against vacuum before and after re--hydration in D2O vapor did not agree. It was only after subsequent re--hydration in saturated H2O vapor that the initial and final reflectivity curves against vacuum superimposed. We will discuss our findings in the context of polyion complex formation, interdigitation and film imperfections.