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

Abstract

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