Effects of interfacial tension on formation of poly(ethylene oxide)-block-polystyrene micelles from emulsions

Abstract

In this report, we show that the structure of an amphiphilic block copolymer assembled through the emulsion and solvent evaporation method can be regulated by tuning the interfacial tension with a third solvent. Microspheres were obtained when a poly(ethylene oxide)-block-polystyrene copolymer was self-assembled by emulsification of its chloroform solution in water. Addition of water-miscible tetrahydrofuran or N,N-dimethylformamide into the aqueous phase by 20 vol% was shown to reduce the interfacial tension between chloroform and water significantly, and strings of vesicles became the dominant structure. Addition of ethanol by 15, 50 and 100 vol% was found to produce strings of vesicles, cylinders and microspheres, respectively. Introduction of cyclohexane, a hydrocarbon solvent, into the organic phase of 1,2-dichloroethane increased the interfacial tension with the aqueous phase, and vesicles were observed instead of the strings of spheres obtained previously. The different assembled structures are discussed in terms of interfacial curvature driven by variation in the interfacial tension.