Polyelectrolyte adsorption on oxides. 2. Reversibility and exchange.

We studied the reversibility of the adsorption of polyelectrolytes on oxides by deliberately creating nonequilibrium situations either by changing the experimental conditions or by performing exchange experiments. Subsequently, we monitored the return to the equilibrium situation. Our measurements indicate that polyelectrolyte adsorption on oxides is only partially reversible, due to the strong (electrostatic) interaction with the surface, which slows down reconformation processes. This interaction is weakened, and thereby the reversibility enhanced, by the addition of salt. A model for the structure of adsorbed layers, allowing little reconformation, predicts that heterogeneous layers are formed.