Berlin 2005 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 30: POSTER: Chemical physics
CPP 30.48: Poster
Dienstag, 8. März 2005, 16:30–18:30, Poster TU D
Chain stratification and anisotropy in polyelectrolyte multilayers — •Abbass Kazemi1,2 and Monika Schönhoff1,2 — 1Institut für Physikalische Chemie, WWU Münster, Corrensstr.30, D-48149 Münster — 2Max-Planck-Institut für Kolloid- und Grenzflächenforschung, D-14424 Golm
Polyelectrolyte multilayers (PEMs) prepared by self-assembly form materials in which the chains are adsorbed in 2-dimensional monomolecular layers. However, structural investigations show a strong interdigitation of adjacent layers, which contradicts the picture of 2-dimensional chains. The chain conformation is studied here by extracting order parameters (S2) of the out-of-plane orientation distribution of polymer segments, i.e. the out-of-plane anisotropy, from UV linear dichroism. Polystyrene sulfonate (PSS) is employed as the anionic component, while the chain stiffness of the cationic component as well as the salt concentration and the number of layers are varied. The results show that the side groups are preferentially oriented in the direction of the surface normal. With increasing layer number, the order parameter decreases for most PEM systems, and reaches a plateau. The salt-dependence is in agreement with existing models of the chain conformation in multilayers. An interesting point is that even for large layer numbers and high salt concentration, no isotropic order is obtained. The order parameters reach values around 0.35, well above 0, implying that the chain conformation is rather 2-dimensional, with well-ordered segments preferentially oriented along the surface normal. This new result clearly contradicts existing views of PEMs as locally isotropic complexes.