The “crew-cut” aggregates of polystyrene- b-poly(ethylene oxide)- b-polystyrene triblock copolymers in aqueous media

Abstract

In this paper, the “crew-cut” aggregates in aqueous media formed by polystyrene (PS)- b-poly(ethylene oxide) (PEO)- b-PS triblock copolymers were presented. The polymers used are PS 43- b-PEO 45- b-PS 43, and PS 40- b-PEO 136- b-PS 40 triblock copolymers (the subscripts are the degree of polymerization). The several factors affecting the aggregation behaviors have been investigated. The multiple morphologies, including vesicles, large compound vesicles, large compound micelles (LCMs), and so on, were obtained by altering the solvents, solvent composition, annealing time, and copolymer composition. The self-assembled aggregates were characterized with a combination of conventional transmission electron microscope and atomic force microscope techniques. It was found that vesicles were formed when making colloids from the PS 43- b-PEO 45- b-PS 43 solutions of THF, dioxane, THF–water, and dioxane–water, while LCMs were obtained in the case of preparing aggregates from the copolymer solutions of DMF and DMF–water. In addition, the larger compound vesicles and a few aggregates with the complex structures were observed using neat dioxane and THF as initial solvents, respectively. Also, prolonging the annealing time was favorable to the formation of vesicles. Furthermore, some unclosed vesicles were observed, which suggested that the vesicles were transformed from the bending of lamellae.