Controlling domain orientation of liquid crystalline block copolymer in thin films through tuning mesogenic chemical structures

ABSTRACT Controlling the macroscopic orientation of nanoscale periodic structures of amphiphilic liquid crystalline block copolymers (LC BCPs) is important to a variety of technical applications (e.g., lithium conducting polymer electrolytes). To study LC BCP domain orientation, a series of LC BCPs containing a poly(ethylene oxide) (PEO) block as a conventional hydrophilic coil block and LC blocks containing azobenzene mesogens is designed and synthesized. LC ordering in thin films of the BCP leads to the formation of highly ordered, microphase‐separated nanostructures, with hexagonally arranged PEO cylinders. Substitution on the tail of the azobenzene mesogen is shown to control the orientation of the PEO cylinders. When the substitution on the mesogenic tails is an alkyl chain, the PEO cylinders have a perpendicular orientation to the substrate surface, provided the thin film is above a critical thickness value. In contrast, when the substitution on the mesogenic tails has an ether group the PEO cylinders assemble parallel to the substrate surface regardless of the film thickness value. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 532–541 This work demonstrates the ability of a functional substitution on the tail of the mesogens of a liquid crystalline block copolymer (LC BCP) to drive the orientation of the domains of the block copolymer when it self‐assembles in a thin film. The effect is demonstrated with a series of LC BCPs that have either hydrocarbon groups or ether groups attached to the tail of the azobenzene group in the liquid crystalline block.