Self-assembly of Block Copolymers with Ionic Liquid Crystals in Thin Films*

Block copolymers (BCPs) self-assembly leads to plenty of promising applications in the area of electronics and energy storage. Thus, improving the ordering of BCP is crucial to optimize its performance in different applications. Adding ionic liquids (ILs) to BCPs has been reported a facile method to realize fast ordering because of its plasticization effect and wetting characteristics tunability. With similar chemical structure to ILs, ionic liquid crystals (ILCs) are liquid-crystalline salts also consisting of cations and anions. Differently, liquid-crystalline nature and thermotropic transition provide ILC with more fascinating features than IL when it is added to BCP. However, BCP/ILC system has not been well studied as BCP/IL system does. In this study, the effect of ILC additives on the self-assembly of BCP, PS-b-PMMA, under different annealing conditions has been investigated by using atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). We observed a drastic change of ILC selective swelling behavior during its thermotropic transition. Moreover, it can be highlighted that ILC enhances the ordering in BCP without enlarging the domain size after the zone annealing.