Ionic strength and curvature effects in flat and highly curved polyelectrolyte brushes

Adsorption of poly(tert-butylstyrene)/poly(styrenesulfonate) diblocks on polystyrene latices from water is reported and interpreted with scaling theories to demonstrate the effects of ionic strength and curvature on layer thickness. The adsorbed amount increases with ionic strength from no added salt to 0.1 M, forming a dense polyelectrolyte brush. The influence of particle radius on layer thickness is correlated quantitatively via the Daoud-Cotton model, but the effect on surface coverage is obscured by uncontrolled aspects of surface chemistry. Decreasing the ionic strength dramatically increases the dimensions of polyelectrolyte micelles and adsorbed layers; the sensitivity, while strongly coupled with curvature, is overestimated by all existing theories. A simple scaling theory that accounts for electrostatic excluded volume more appropriately captures the trends qualitatively.