Surface potential of spherical polyelectrolyte brushes in the presence of trivalent counterions

We consider the ζζ-potential and the effective charge of spherical polyelectrolyte brushes (SPBs) in aqueous solution in the presence of trivalent europium ions. The SPB consists of a polystyrene core of ca. 250 nm diameter onto which long chains of the strong polyelectrolyte poly(styrene sulfonate) are grafted (contour length: 82 nm). At low concentration of EuCl3EuCl3 the chains are stretched to nearly full length. If the concentration of the trivalent ions is raised, the surface layer of the polyelectrolyte chains collapses. The ζζ-potential of the SPB is calculated from the electrophoretic mobilities measured at different concentrations of EuCl3EuCl3. At the collapse, ζζ decreases by the partial neutralization of the charges by the trivalent ions. The experimental ζζ-potential thus obtained agrees with the theoretical surface potential ΨtheoΨtheo calculated for the effective shear plane by a variational free energy model of the SPB.

The electrophoretic mobility of a negatively charged brush layer in the presence of trivalent Eu3+Eu3+ counterions is measured. The experimental (ζ)(ζ) is compared to the theoretical (Ψtheo)(Ψtheo) surface potential derived from a simple statistical–mechanical model.Figure optionsDownload as PowerPoint slide