Control on the Morphology of ABA Amphiphilic Triblock Copolymer Micelles in Dioxane/Water Mixture Solvent

This work offers a typical understanding of the factors that govern the nanostructures of poly(4-vinyl pyridine)-b-polystyrene-b-poly(4-vinyl pyridine) (P4VP-b-PS-b-P4VP) block copolymers (BCs) in dioxane/water, in which water is a selective solvent for the P4VP block. It is achieved through an investigation of the amphiphilic triblock copolymer micelles by variation of three different factors, including water content (above CWC but under the immobile concentration), temperature (ranging from 20 A degrees C to 80 A degrees C), and copolymer composition (low and high PS block length). Transition of bead-like micelles to vesicles is observed with the increase of water content due to the increase of interfacial energy between the copolymer and the solvent. Effect of temperature superposed on that of water content results in various morphologies, such as beads, fibers, rods, capsules, toroids, lamellae, and vesicles. The interfacial tension between the BC and the solvent increases with the increase of water content but decreases with the increase of temperature, indicating that the micellar morphologies are resulted from the competitive interplay between the temperature and the water content and always change in a direction that decreases the interfacial energy. Based on the micellar structures obtained in this work and the effects of temperature superposed on water concentration, a diagram of phase evolution of different micellar morphologies is illustrated here, covering the temperature range from 20 A degrees C to 80 A degrees C and the water content changing from 20 vol% to 35 vol%. For the investigation of BC composition, morphological transition of vesicle-to-fiber, for high PS length, is observed as compared with bead-to-capsule for low PS length, as the temperature changes from 20 A degrees C to 80 A degrees C. Our research complements the protocols to control over the morphologies and the phase diagram describing P4VP-b-PS-b-P4VP micellar nanostructures in aqueous solution.