Macromolecules, Vol.51, No.5, 2099-2109, 2018
Temperature-Dependent Order-to-Order Transition of Polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene Triblock Copolymer under Multilayered Confinement
The order-to-order transition (OOT) plays a key role in the nanotechnological applications of block copolymer (BCP) and is dramatically dependent on the spatial environment. A multilayer-confined space has been fabricated by layer-multiplying coextrusion technology to investigate the OOT mechanism of polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymer (SEBS) under multilayered confinement. The parallel oriented ordering front, whose OOT temperature is lower than that of the bulk due to higher free energy, is induced by the "substrate surface effect" in the SEBS layers of the multilayer specimens. The OOT temperature of SEBS is mainly decided by the volume fraction of ordering front. The propagation distance maximum of the "substrate surface effect" is about 220 nm. Only when the thickness of SEBS layer is less than this critical value is the whole SEBS layer fully filled with the ordering front. As a result, the OOT temperature first decreases rapidly and then tends to be a constant value with the decrease of layer thickness. This turning point of layer thickness is found to locate around 220 nm. Finally, the change of transition temperature region with the layer thickness has been explained by the fact that the bulk, thin layer samples (less than turning point) and thick layer samples (more than turning point) have different OOT mechanisms.