Ordering kinetics between HEX and BCC microdomains for SI and SIS block copolymers

Abstract

Order to order transitions (OOT) From hexagonally packed cylindrical (HEX) microdomains to body centered cubic (BCC) microdomains and vice versa, for a polystyrene-block-polyisoprene (SI-CI) and a polystyrene-block-polyisoprene-block-polystyrene (Vector 4111) were investigated by rheology and synchrotron small angle X-ray scattering experiments using one dimensional detector (1-D SAXS) and an imaging plate (2-D SAXS). The weight fraction of PS block in both block copolymers was almost the same (0.18), and the molecular weight of SI-Cl was almost half that of Vector 4111. The cylindrical axis of the HEX microdomains in the as-cast samples of both block copolymers was aligned toward the flow direction in a macroscopic scale when an oscillatory shearing with a large strain amplitude and a low frequency was applied to the samples. Interestingly, we found, via 2-D SAXS and rheology, that the initial cylinder axis of the HEX microdomains in the aligned sample was significantly changed once the sample was heated to the region corresponding to BCC microdomains and cooled to the temperature in HEX region without a shearing. Because of the existence of bridge (tail) conformation of PI block, the transition from HEX to BCC microdomains for Vector 4111 took place slowly compared with SI-CI. The OOT from HEX to BCC microdomains was found to be much easier process than that from the reverse transition of BCC to HEX microdomains.