Adsorption of Hydrophobic Polyelectrolytes at Oppositely Charged Surfaces

Abstract

We develop a scaling theory of adsorption of necklace-like hydrophobic polyelectrolytes at an oppositely charged hydrophilic and hydrophobic surfaces. At low surface charge densities we predict a two-dimensional adsorbed layer with thickness determined by the balance between electrostatic attraction to the charged surface and chain entropy. At high surface charge densities we expect a 3-dimensional layer with polymer density profile determined either by the balance between two-body monomer−monomer attraction or by electrostatic attraction to the surface and three-body monomer−monomer repulsion. These different stabilizing mechanisms result in the nonmonotonic dependence of the layer thickness on the surface charge density. For adsorption of polyelectrolyte chains from salt solutions the screening of the electrostatic repulsion between adsorbed polyelectrolyte chains results in large overcompensation of the surface charge for two-dimensional adsorbed layers. The polymer surface coverage for this regime increases with increasing salt concentration. The opposite trend is predicted for 3-D adsorbed layers where the polyelectrolyte surface excess decreases with increasing salt concentration.