Preparation of lamella-structured block-copolymer particles and their irreversible lamella-disorder phase transition

In this report, we investigated the effect of annealing on the phase separation structures formed in the block-copolymer nanoparticles. The nanoparticles with the lamellar structures were prepared by evaporation of tetrahydrofuran (THF) from the THF/water solution of poly(styrene-b-isoprene), in which each polymer segment has almost same length. Scanning transmission electron microscope (STEM) observation of the block-copolymer nanoparticles and their cross-section image revealed that the consecutive lamellar structure was formed one-directionally in the nanoparticles. When the suspension of lamellar-structured nanoparticles was annealed at 50 °C for 10 h, the lamellar phase changed to the disorder structures. This transition was irreversible. This result shows the lamellar structure formed in nanoparticles is less stable than that in the planar film.