Single Polyelectrolyte Layers Adsorbed at High Salt Conditions: Polyelectrolyte Brush Domains Coexisting with Flatly Adsorbed Chains

Abstract

AFM is used to measure the surface forces and to image sodium poly(styrenesulfonate) (PSS) layers physisorbed from 1 M NaCl solution on different length scales within one experiment. Domains of PSS brushes coexist with flatly adsorbed PSS. For degree of polymerization N = 380, the brush area fraction is 6%. With increasing degree of polymerization, brush area fraction and domain size increase, whereby the domain radii vary between 50 nm and 1.5 μm. Lateral homogeneous brush layers are found for a degree of polymerization exceeding 1100. The colloidal probe technique reveals that the surface forces are a superposition of steric and electrostatic forces; their respective contribution is determined by the brush area fraction. A comparison with literature demonstrates that adsorbed PSS brushes show the same scaling behavior as end-grafted PSS brushes. We develop a model for the adsorption of polyelectrolytes in which not the whole chain but only a fraction of the monomers adsorbs onto the surface. Thereby, we show that partial adsorption can lead to stable conformations and calculate scaling laws for the fraction of adsorbed monomers and the distance between the chains dangling into solution.