Adsorption of tethered polyelectrolytes onto oppositely charged solid-liquid interfaces

We consider an equilibrium structure of a monolayer formed by weakly charged polyelectrolyte chains tethered to the oppositely charged interface. The interface is characterized by an immobile charge spatially distributed in a sublayer of finite thickness submerging tethered polyions. The Coulomb attraction of tethered polyions to the surface induces their adsorption. Three complementary theoretical approaches (scaling, analytical self-consistent-field approach, and numerical self-consistent-field model) are put to the problem in order to provide a complete description of the behavior of this complex charged interface. Both the value of the charge immobilized at the surface and the ionic strength of the solution influence the conformations of grafted polyelectrolytes in a significant way. It is shown that the height of sufficiently densely grafted polyelectrolyte monolayers ("polyelectrolyte brushes") can depend nonmonotonically on the value of the ionic strength of the solution. The relevance of the system to help understanding complex interfaces, as they occur in, e.g., casein micelles, is discussed.