Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: Poster: Charged Soft Matter

CPP 10.10: Poster

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

Odd-even and even-odd effect in polyelectrolyte multilayers observed with multiple angle ellipsometry — •Peter Nestler, Stephan Block, and Christiane A. Helm — Inst. für Physik, Uni Greifswald, Felix-Hausdorff-Str. 6, D-17487 Greifswald

Within a liquid cell the growth of polyelectrolyte multilayers (PEMs) by sequential adsorption of oppositely charged polyelectrolytes is observed using ellipsometry. The polyanion is poly(styrenesulfonate) (PSS), the polycation poly(allylamine hydrochloride) (PAH), and the substrate a Si wafer. The salt content is varied between 1 and 4 mol/L NaCl, the preparation temperature between 20 and 55°C. On rise of the temperature, the thickness of a polycation/polyanion bilayer increases. After each adsorption step the PEM thickness and index of refraction is determined at several angles of incidence. A film which is always immersed in aqueous solution is at least 40% thicker than a film which is dried in air. The increase in PEM thickness after an adsorption step shows an alternating pattern (even-odd effect) due to an unequal PSS- and PAH-contribution to the thickness of one double layer. At temperatures up to 45°C, the outermost PSS layer is thicker. Then a cross-over from even-odd to odd-even effect occurs, and a top PAH layer is thicker than a top PSS layer. A similar even-odd effect is observed in the refractive index of the PEM and allows an estimation of the refractive index of the outermost monolayer. At high temperature, the thicker outermost polyelectrolyte layer always has a higher water content, irrespective of its chemical nature.