Phase Transition of Binary Block Copolymer Blends and Pressure Dependence

Three types of phase transitions were identified in the miscible block copolymer blends of polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA) and polystyrene-b-poly(n-hexyl methacrylate) (dPS-b-PnHMA), which were known as order-to-disorder transition (ODT), lower disorder-to-order transition (LDOT), and upper order-to-disorder transition (UODT). Interestingly, the closed-loop transition was found in a specific volume range (0.511~0.514) of one block. Small-angle X-ray scattering (SAXS) and depolarized light scattering (DPLS) were used to measure the composition-dependent phase transitions, and transmission electron microscopy (TEM) was used to confirm each results. These phase transition boundaries were demonstrated in a 3D phase transition diagram of the BCP blends with other variable of (d)PS volume fraction. Such diverse phase transitions and the closed-loop transition showed high pressure-sensitive baroplastic nature, arising from entropic compressibility.