Temperature-Dependent Order-to-Order Transition of\nPolystyrene-<i>block</i>-poly(ethylene-<i>co</i>-butylene)-<i>block</i>-polystyrene Triblock Copolymer\nunder Multilayered Confinement

Abstract

The\norder-to-order transition (OOT) plays a key role in the nanotechnological\napplications of block copolymer (BCP) and is dramatically dependent\non the spatial environment. A multilayer-confined space has been fabricated\nby layer-multiplying coextrusion technology to investigate the OOT\nmechanism of polystyrene-<i>block</i>-poly­(ethylene-<i>co</i>-butylene)-<i>block</i>-polystyrene triblock\ncopolymer (SEBS) under multilayered confinement. The parallel oriented\nordering front, whose OOT temperature is lower than that of the bulk\ndue to higher free energy, is induced by the “substrate surface\neffect” in the SEBS layers of the multilayer specimens. The\nOOT temperature of SEBS is mainly decided by the volume fraction of\nordering front. The propagation distance maximum of the “substrate\nsurface effect” is about 220 nm. Only when the thickness of\nSEBS layer is less than this critical value is the whole SEBS layer\nfully filled with the ordering front. As a result, the OOT temperature\nfirst decreases rapidly and then tends to be a constant value with\nthe decrease of layer thickness. This turning point of layer thickness\nis found to locate around 220 nm. Finally, the change of transition\ntemperature region with the layer thickness has been explained by\nthe fact that the bulk, thin layer samples (less than turning point)\nand thick layer samples (more than turning point) have different OOT\nmechanisms.