Weak Polyelectrolyte Brushes as Substrates for the Formation of Surface-Attached Polyelectrolyte−Polyelectrolyte Complexes and Polyelectrolyte Multilayers

Abstract

Monolayers of polyelectrolyte complexes are generated at solid surfaces using covalently attached monolayers of weak polyelectrolyte molecules (“polyelectrolyte brushes”) exposed to aqueous solutions of oppositely charged polyelectrolytes. The adsorption of the charged polymers onto the brush-coated substrate is measured as a function of deposition time, pH value, salt concentration, and concentration of the polymer solution as well as the thickness of the surface-attached monolayer. It is shown that the adsorbed amount depends critically on the pH value of the solution and shows a pronounced maximum at intermediate salt concentrations. Upon exposure to an oppositely charged polyelectrolyte solution, the brush adsorbs large amounts of the polyelectrolyte and form thick layers in the same range as the thickness of the brush layer. Additionally, the thus-obtained layers are used as substrates for the formation of polyelectrolyte multilayers following a standard layer-by-layer approach. It is shown that the total film thickness scales linearly with the number of dipping cycles and that even the outermost layer is strongly correlated to the thickness of the brush layer which is used as the substrate.