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SYPF: Struktur und Dynamik in dünnen Polymerfilmen

SYPF 2: Poster Session

SYPF 2.32: Poster

Donnerstag, 14. März 2002, 09:00–18:00, Poster B

Influence of charge density and ionic strength on the multilayer formation of strong polyelectrolytes — •Ulrike Voigt and Regine v. Klitzing — Stranski-Laboratorium, TU Berlin, Strasse d. 17. Juni 112, 10623 Berlin

The polymer films presented in this study were made by alternate adsorption of polyanions (PSS) and polycations (PDADMAC-stat-PNMVA) from aqueous solution. The advantage of this layer-by-layer deposition is, that the thickness can be tuned by the number of adsorbed layers and the ionic strength. With increasing salt concentration the film thickness increases due to electrostatic intrachain and interchain screening of charges. This ocurs up to high ionic strength (above 1 mol/L) although the charges are totally screened in this regime. This rises the question if electrostatic attraction is needed for the formation of multilayers. The influence of ionic strength and polymer charge density on the multilayer formation of strong polyelectrolytes is investigated by ellipsometry and AFM. To first approximation the adsorption behavior as a function of the degree of charge, f, is binary: For f ≤ 50% the films are one order of magnitude thinner than for f ≥ 75%. This is due to a threshold of charge overcompensation after each adsorption step which seems to be at f between 50 and 75 %. The position of the threshold is not influenced by the addition of salt.