Fabrication of Stable Nanocylinder Arrays in Highly Birefringent Films of an Amphiphilic Liquid-Crystalline Diblock Copolymer

Abstract

An amphiphilic liquid-crystalline diblock copolymer (LCDC) with a highly birefringent cyanobiphenyl (CB) group as a mesogen was prepared by atom-transfer radical polymerization. The obtained LCDC showed a well-defined structure and a narrow molecular-weight distribution. In its spin-coated films, both liquid-crystalline (LC) alignment and microphase-separated nanostructures were systematically studied. Random LC arrangement and ambiguous microphase separation were observed in as-prepared films because of the high viscosity at room temperature. Upon annealing of the films in an isotropic phase of the LCDC, the CB mesogens self-organized into a smectic texture of a conic fan and the microphase separation proceeded completely. It is the supramolecular cooperative motion that enables the LCDC to hierarchically assemble into a regular patterning of normally aligned nanocylinders to the substrate, dispersed in the out-of-plane-oriented mesogens. With the help of homogeneous alignment of the CB groups induced by a rubbing technique, uniform patterning of highly ordered nanocylinders parallel to the rubbing direction was successfully fabricated in the plane. The fabricated perpendicular and parallel patterning of nanocylinders dispersed in the highly birefringent films with the CB block as the majority phase show good stability under room light, indicating their potential applications as nanotemplates for preparing advanced nanoscaled materials.