Electrostatically Controlled Swelling and Adsorption of Polyelectrolyte Brush-Grafted Nanoparticles to the Solid/Liquid Interface

Adsorption of 20 nm diameter silica nanoparticles grafted with a high density brush of the weak polymeric base poly­(2-(dimethylamino)­ethyl methacrylate) (SiO₂-g-PDMAEMA) to the silica/aqueous interface was investigated using ellipsometry and streaming potential measurements. We measured SiO₂-g-PDMAEMA adsorption to negatively charged silica surfaces in 1–100 mM sodium chloride solutions in the pH range 5–10 to investigate the role of electrostatics in the adsorption mechanism. In this system pH and ionic strength determine not only the charge density of the silica adsorption substrate but also the degree of ionization and swelling of the PDMAEMA brushes on the nanoparticles, resulting in nonmonotonic dependences of the extent of adsorption on pH and ionic strength. SiO₂-g-PDMAEMA displays significantly different adsorption behavior from the linear PDMAEMA analogue, most notably in terms of a strongly hysteretic adsorption response to altered pH and a greater tendency to adsorb under weak surface attraction conditions that prevail at high pH.