polymer adsorption (1). Both regimes, as well as intermedi-Adsorption of a low linear charge density cationic polyacrylate situations in which Gc s dependencies exhibit a maxiamide (CPAM) onto monodisperse silica particles has been studmum, have been observed in experiments (2-4). Competiied over a wide range of KCl concentration (10 03 -1 M) and pH tive adsorption of counterions was shown to have a pro-(4-9). In parallel the surface charge density of silica particles nounced effect on polyelectrolyte adsorptivity at high salt with and without adsorbed polyelectrolyte has been determined. content (2, 4). In Ref. (2) the influence of electrolyte con-The adsorbed amount ( G) as a function of electrolyte concentracentration on the interfacial conformation of polyions was tion (c s ) exhibits a maximum at c s Γ 0.1 M. As pH increases from also explored and good agreement between experiment and 4 to 6, G increases and then either reaches a plateau (c s Β£ 0.1 M)
or decreases (c s ΓΊ 0.1 M). These features can be rationalized in theory was obtained (at least within the framework of the terms of the interplay between the different factors that govern self-consistent-field theory (5-7)).
polyelectrolyte adsorption. The effect of polyelectrolyte adsorption
While this situation might be considered reasonably satison the surface charge density of silica is largest at low c s . It defactory, the problem of the mutual influence of polyelectrocreases with increase of the salt content and vanishes at c s ΓΊ 0.1 lyte adsorption and surface charge density of the substrate M. This suggests that at electrolyte concentrations lower than 0.1 has remained unresolved. In theoretical calculations the sim-M, the polyelectrolyte plays a dominant in surface charge regulaplifying conditions of constant surface charge (s 0 Γ
const) tion. The ratio of the adsorbed polyelectrolyte charge to total suror constant surface potential (C 0 Γ
const) are adopted (1, 2, face charge is close to unity at high pH. It increases drastically with decreasing pH and increasing salt. A large overcompensation 8). This avoids complications that occur when information of the substrate charge by polyelectrolyte at these conditions is concerning real changes in s 0 and C 0 upon adsorption is not established in the present work.