Superlattice Structure from Self-Assembly of High-χ Block Copolymers via Chain Interdigitation

Flexible and shape-tunable features of block copolymers (BCPs) with high Flory-Huggins interaction parameters (high,' value) have drawn intensive attention due to their rich phase behaviors. Herein, this work aims to examine a fascinating superlattice structure obtained from the self-assembly of high-,' BCP, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), as evidenced by reciprocal-space imaging from small-angle X-ray scattering (SAXS) and by real-space imaging from transmission electron microscopy (TEM). Surprisingly, an interesting reversible order-order transition from superlattice structure with chain interdigitation to typical lamellae with bilayer texture can be identified by in situ temperature-resolved SAXS. In contrast to the diblock (PS-b-PDMS)(n )(n = 1), the forming superlattice structure will be greatly impeded in star-block (PS-b-PDMS)(n) (n = 3 and 4) with equivalent arm length, suggesting a topological effect on self-assembly due to their star-shaped architecture. Accordingly, a lamellae-forming PS-b-PDMS with chain interdigitation (wet-brush-like chain packing) was proposed to be the origin of the forming superlattice structure. This finding provides an insight for the possible model with ladder-like structure and corresponding transformation mechanisms of high-,' BCPs. Also, the topological effect from star-block architecture may play an important role to justify the formation of such a unique self-assembled texture. These results implicitly explore the feasibility to acquire a superlattice structure from a simple coil-coil diblock copolymer.

Automated summary

This study investigates the self-assembly of high-Flory-Huggins BCP and reveals a reversible order-order transition in the superlattice structure. The topological effect of star-block architecture is found to play a crucial role in the formation of the unique self-assembled texture. These findings provide new insights into the structure of high-Flory-Huggins BCPs.