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CP: Chemische Physik
CP 17: Postersitzung Transportprozesse durch Grenzflächen und Membranen
CP 17.5: Poster
Tuesday, March 18, 1997, 18:30–21:15, FBH
Molecular Mechanisms Controlling the Self-Assembly-Process of Polyelectrolyte Multilayers — •Klaus Lowack2 and Christiane A. Helm1 — 1Fachrichtung Kristallographie, Universität des Saarlandes, 66041 Saarbrücken — 2Institut für Physikalische Chemie, Johannes Gutenberg-Universität, 55099 Mainz
The distance dependent interaction between polyelectrolyte-covered mica surfaces in aqueous solution was investigated with the surface forces apparatus. We find (i) the over-all surface charge changes sign, whenever an oppositely charged polyelectrolyte is adsorbed onto a surface. (ii) Tails and loops of the polyions adsorbed onto the mica surface dangle into the bulk phase, providing a small steric force and, if polycations and poyanions coexist on the surface, a strong short range attractive force due to ion-pair formation is found. (iii) After adsorption, there may be still non-occupied binding places on the surface. We show that these adsorption-properties regulate the build-up of polyelectrolyte multilayers. (i) Due to the charge inversion of the surface, the adsorbed amount of polyelectrolyte is kinetically limited by electrostatic repulsion between the surface and the polyelectrolyte molecules in the solution, not (ii) by the available binding places on the surface. Thus, the thermodynamics of the polyion adsorption leads both to the constant thickness of each additional layer and to the stability of the layers in various environmental conditions. (iii) We provide evidence, that the binding of an additional polelectrolyte layer onto a multilayer occurs by ion-pair formation.