Solvent quality dependent interactions between adsorbed block copolymers measured by AFM

This paper describes experiments conducted with an atomic force microscope to investigate the manner in which the steric interactions between an adsorbed layer of the block copolymer synperonic F127 (an ABA copolymer of ethylene and propylene oxide) are modified when the solvency conditions are gradually changed from good to poor. The solvent quality was adjusted by varying either the temperature or the electrolyte concentration. By fixing one of the aforementioned parameters such as temperature, measurements were conducted at various electrolyte (sodium sulfate) concentrations. Alternatively at a fixed temperature, the electrolyte concentration was increased. It was found that as the solvency for the stabilising polymer, poly (ethylene oxide) (PEO) decreased the range of the interaction decreased and that at sufficiently high sodium sulfate concentrations, or temperature, the interaction switched from being repulsive to being attractive. The results were compared to the cloud points of F127, low molecular weight PEO, and the critical flocculation temperatures for polystyrene latex bearing the same adsorbed polymer adsorbed. The point at which the polymer interaction forces changes from repulsive to attractive, compares to, but is lower than the lower consulate solution temperatures (LSCT) for the copolymer and critical flocculation temperatures (CFT) for PEO stabilised polystyrene latex particles.