Adsorption of polyelectrolytes at oppositely charged surfaces

We have developed a scaling theory of polyelectrolyte adsorption at an oppo sitely charged surface. At low surface charge densities, we predict two-dim ensional adsorbed layers with thickness determined by the balance between e lectrostatic attraction to the charged surface and chain entropy. At high s urface charge densities, we expect a 3-dimensional layer with a density pro file determined by the balance between electrostatic attraction and short-r ange monomer-monomer repulsion. These different stabilizing mechanisms resu lt in a nonmonotonic dependence of the layer thickness on the surface charg e density. For adsorption of polyelectrolyte chains from salt solutions, th e screening of the electrostatic repulsion between adsorbed polyelectrolyte chains results in large overcompensation of the surface charge for two-dim ensional adsorbed layers. At higher salt concentrations this overcompensati on of the surface charge by the 2-d adsorbed layer is independent of the or iginal surface charge and depends only on the fraction of the charged monom ers on the polyelectrolyte chains and increases with ionic strength. The po lyelectrolyte surface excess in 3-d adsorbed layers increases at low ionic strength and decreases at higher ionic strength.