Adsorption of Polyether Block Copolymers at Silica-Water and Silica-Ethylammonium Nitrate Interfaces

Atomic force microscope (AFM) force curves and images are used to characterize the adsorbed layer structure formed by a series of diblock copolymers with solvophilic poly(ethylene oxide) (PEO) and solvophobic poly(ethyl glycidyl ether) (PEGE) blocks at silica-water and silica-ethylammoniun nitrate (EAN, a room temperature ionic liquid (IL)) interfaces. The diblock polyethers examined are EGE109EO54, EGE113EO115, and EGE104EO178. These experiments reveal how adsorbed layer structure varies as the length of the EO block varies while the EGE block length is kept approximately constant; water is a better solvent for PEO than EAN, so higher curvature structures are found at the interface of silica with water than with EAN. At silica-water interfaces, EGE109EO54 forms a bilayer and EGE113EO115 forms elongated aggregates, while a well-ordered array of spheres is present for EGE104EO178. EGE109EO54 does not adsorb at the silica-EAN interface because the EO chain is too short to compete with the ethylammonium cation for surface adsorption sites. However, EGE113EO115 and EGE104EO178 do adsorb and form a bilayer and elongated aggregates, respectively.