Interactions between polyelectrolyte brushes in free-standing liquid films:: influence of ionic strength

Foam films of charged amphiphilic diblock copolymers are investigated using a thin-film balance. At low polymer concentrations the disjoining pressure shows a continuous exponential decay as a function of the thickness This indicates film stabilization by electrostatic repulsion. At higher polymer concentration stratification occurs with increasing pressure. This is due to the formation of a layer of block copolymer micelles which is pressed out of the film in analogy to usual foam films containing micelles of small surfactant molecules. With increasing salt concentration the film becomes thinner as the charged part becomes more and more coiled and the surface charges more screened.