PUB - Publikationen an der Universität Bielefeld

Foam films of semi-dilute anionic polyelectrolyte solutions containing additionally the cationic surfactant dodecyltrimethylammonium bromide are investigated. The polyelectrolytes used are polystyrene sulfonate (PSS) and acrylamidesulfonate (AAS) as examples of strongly and weakly charged polyions, respectively. The disjoining pressure isotherm results in film stratification well below the critical micelle concentration (CMC) and the critical aggregate concentration (CAC). These pressure oscillations are related to a network of polyelectrolyte chains in the film bulk, and their period to the mesh size. The network can be described by the theory for semi-dilute polyelectrolyte solutions, which is different for the two polyelectrolytes because of different charge densities along the chain. The surfactant has no observable influence on the network. To obtain information about the him interface surface tension measurements at the water-air interface are carried out. In comparison with the pure polyelectrolyte and the surfactant, respectively, the surface tension is much reduced for the mixed systems as a result of the formation of complexes between the surfactant and the polyelectrolyte. The two polymers show different behaviour in saturation of the surface coverage, which leads us to the conclusion that the complexes are different, although the behaviour of the film bulk is not influenced by changes in the interface. (C) 1999 Elsevier Science B.V. All rights reserved.