Hierarchically self-constructed alignment layer of comb-shaped amphiphilic copolymers for spontaneous and stable vertical orientation of liquid crystals

Abstract

Hierarchically self-constructed ordered nanoarchitectures for precise control of molecular alignment has received much attention in a wide range of applications from optoelectronic devices to flexible biosensors. Herein, we present a facile and effective fabrication strategy to create a hierarchically constructed self-alignment layer of comb-shaped amphiphilic copolymers for spontaneous vertical molecular orientation of liquid crystals (LCs). Amphiphilic poly(vinyl 4-heptylbenzoate)-g-poly(vinyl alcohol) (PVHB-g-PVA) as a comb-shaped copolymer was doped to an LC medium, and its interfacial self-assembly on indium tin oxide electrode induced the hierarchical self-constructed alignment layer through hydrophilic interactions of hydroxy groups. In addition, hydrophobic and cooperative interactions of alkyl phenyl moieties in amphiphilic copolymers ensured the stable vertical self-alignment of LC molecules. Compared to conventional polyimide layer, the proposed self-constructed alignment layer afforded high vertical alignment ability for LCs and outstanding device performance in terms of the threshold voltage and response speed. Furthermore, the long-term alignment reliability of the proposed copolymeric self-assemblies was comparable to that of commercial alignment layer.