Control of Regular Nanostructures Self-Assembled in an Amphiphilic Diblock Liquid-Crystalline Copolymer

Abstract

An amphiphilic diblock liquid-crystalline copolymer consisting of poly(ethylene oxide) (PEO) and polymethacrylate containing an azobenzene moiety in the side chain was prepared by atom transfer radical polymerization (ATRP). The specifically-designed chemical constitution and the low molecular-weight polydispersity enable the block copolymer to form a regular microphase-separated nanostructure self-assembled in its bulk films, in which a hexagonal packing of the PEO cylinders normal to the substrates was dispersed in a continuous phase of azobenzene mesogens with out-of-plane alignment. Then a commerically available rubbing technique was first used to control the microphase-separated domains in the copolymer films. By introducing novel supramolecular cooperative motions between ordered azobenzene mesogens and PEO microphase domains, macroscopic array of PEO nanocylinders was regularlly formed along the rubbing direction. Both the dotted and parrallel stripe patterns of PEO nanocylinders were successfully obtained in the same block copolymer.