Thin-Film Self-Assembly of Block Copolymers Containing an Azobenzene-Based Liquid Crystalline Polymer and a Poly(ionic liquid)

By combining reversible addition-fragmentation chain transfer (RAFT) with postfunctionalization and ion exchange, we synthesized a series of block copolymers (BCPs) containing an azobenzene-based liquid crystalline (LC) polymer (PAzo) and an imidazolium-containing poly(ionic liquid) (PIL, PVB(TFSI)) with the volume fraction of PIL (f(PIL)) values ranging from 15.9% to 69.9%. The samples obtained self-assemble into hexagonally packed cylinders (HEX), lamellae (LAM), and the mixed phase with coexisting HEX and LAM. The thin-film self-assembly of the samples PAzo(101)-b-PVB(TFSI)(22) and PAzo(101)-b-PVB(TFSI)(67) was studied systematically. We investigated the assembled structures of the thin films with various initial thicknesses after thermal annealing (145 degrees C for 12 h) or mixed solvent vapor annealing with tetrahydrofuran and n-hexane. Thin films with large-scale uniaxial PIL nanocylinders were obtained, which will greatly broaden the application of IL-based BCPs. Inverse phases were also observed for the thin films with thicknesses less than similar to 120 nm. The different mechanisms of the formation of inverse nanostructures formed in the thinner films under the thermal annealing and mixed solvent vapor annealing conditions were also elucidated.